Biomass-derived carbon quantum dots as sustainable nanosensors for pesticides and toxic metabolites

Abstract

The large-scale application of organophosphate (OP) pesticides poses serious challenges to food safety, environmental sustainability, and human health, creating an urgent need for rapid and sensitive detection technologies. In recent years, carbon quantum dots (CQDs) derived from natural biomass have emerged as environmentally benign fluorescent nanoprobes, offering tunable photoluminescence, high photostability, and versatile surface functionalities. Some CQD fluorescence sensors of OP pesticides use the quenching mechanisms of inner filter effect (IFE), photoinduced electron transfer (PET), and Förster resonance energy transfer (FRET), with detection limits as low as 0.1–5 ppm towards compounds as varied as methyl parathion, chlorpyrifos, and malathion. In real-sample studies, the sensors obtained satisfactory recovery rates between 88% and 104% in matrices with the use of waters, soil, and fruit extracts with satisfactory reproducibility (RSD < 5%). However, most existing strategies are still limited to controlled lab environments with limited selectivity, stability, and tolerance to the matrix. Additionally, although there has been notable development in the sensing of pesticides, the sensing of toxic OP metabolites such as p-nitrophenol (PNP), a key biomarker of exposure, has still attracted relatively minor interest. This review critically summarizes the recent developments in biomass-derived CQDs for OP pesticide and metabolite detection, highlighting the influence of precursor composition, surface functionalization, and optical quenching pathways on sensing performance. Particular emphasis is placed on structure–function relationships, fluorescence quenching mechanisms, and real-sample validation. By delineating current challenges and opportunities, this review outlines strategies for designing robust, portable, and sustainable CQD-based sensors capable of bridging the gap between proof-of-concept research and practical applications in food safety, environmental monitoring, and human health protection.

---

Environmental significance

Carbon quantum dots derived from renewable biomass provide an eco-friendly alternative to conventional pesticide detection methods that are costly and resource-intensive. Their tunable fluorescence and defect-rich surfaces enable sensitive monitoring of organophosphate residues and their toxic metabolite p-nitrophenol across water, soil, food, and biological samples. By integrating green synthesis with advanced sensing mechanisms, these nanosensors reduce environmental burden while enhancing exposure assessment. This work demonstrates the potential of CQDs to bridge laboratory innovations with sustainable solutions for food safety, ecological security, and public health.

1. Introduction

Pesticides have long played a crucial role in sustaining agricultural productivity and global food security. Since the mid-twentieth century, their widespread application has helped reduce crop losses and control insect-borne diseases. Major classes include organochlorines, carbamates, and organophosphates (OPs), each possessing distinct chemical properties and biological effects. While pesticides have undeniable benefits, their excessive and often indiscriminate use has released toxic, persistent, and bio-accumulative compounds into the environment. Among them, OPs are comparatively biodegradable yet acutely toxic to non-target organisms, including humans¹ (Fig. 1). Chronic low-level exposure to OPs has been associated with multiple health risks such as endocrine disruption, immune suppression, reproductive toxicity, and neurodegenerative diseases including Parkinson's and Alzheimer's.² Less than 0.1% of applied pesticides reach their intended targets; the rest contaminates soil, water, and air, driving bioaccumulation and long-term ecological imbalance.^3,4 OPs, used extensively in agriculture and vector control, act by inhibiting acetylcholinesterase (AChE), causing overstimulation of cholinergic receptors and subsequent neuromuscular paralysis.^5,6 Common examples like malathion, parathion, chlorpyrifos, and diazinon differ in persistence and toxicity.^7,8

Fig. 1 Classification of pesticides according to their toxicity levels, ranging from low-toxicity biochemical pesticides to highly toxic and persistent organochlorines.

During environmental degradation, OPs generate toxic by-products such as p-nitrophenol (PNP), a priority pollutant and reliable biomarker of exposure due to its persistence and bioavailability. Urinary PNP levels in exposed individuals have been correlated with OP contact, and its toxic effects include haemolysis, hepatotoxicity, and nephrotoxicity.^9–11 Accurate and rapid detection of OPs and PNP in environmental and biological matrices is therefore essential for risk assessment and exposure monitoring. Although analytical methods such as HPLC, GC–MS, and capillary electrophoresis provide excellent sensitivity and selectivity,¹² they are time-intensive, instrumentally demanding, and unsuitable for on-site testing.¹³ These limitations have accelerated research on nanomaterial-based sensors that offer rapid, portable, and cost-effective alternatives.

Carbon dots (CDs) or carbon quantum dots (CQDs) are emerging as a versatile class of zero-dimensional carbon nanomaterials (<10 nm) with tunable photoluminescence, high photostability, and excellent aqueous solubility¹⁴ Biomass-derived CQDs are particularly attractive for sustainable sensing applications due to their eco-friendly synthesis, low toxicity, and cost efficiency.¹⁵ Their surface functional groups (–OH, –COOH, –NH₂) enable strong interactions with OP molecules, producing fluorescence quenching through photo-induced electron transfer (PET), fluorescence resonance energy transfer (FRET), or inner-filter effect (IFE) mechanisms^16,17 (Fig. 2).

Fig. 2 Schematic representation of the green synthesis of carbon quantum dots (CQDs) from biomass and their application in pesticide detection via fluorescence quenching mechanisms.

These fluorescence responses scale proportionally with analyte concentration, enabling quantitative detection. Advances in green synthetic strategies especially microwave-assisted and room-temperature approaches using renewable biomass precursors have further improved CQD yield, reproducibility, and environmental compatibility.¹⁸ Heteroatom doping (N, S, B, Mn) and hybridization with metal oxides (ZnO, TiO₂) enhance selectivity and sensitivity toward specific OPs.¹⁹ CQD-based fluorescent sensors now routinely achieve nanomolar detection limits and rapid response times across complex matrices such as soil, water, and urine.^20,21

Compared with other nanosensing platforms such as metal nanoparticles, metal–organic frameworks (MOFs), and polymer-based composites, carbon quantum dots (CQDs) exhibit a unique combination of optical tunability, chemical stability, and biocompatibility that enhances their analytical performance.²² Metal nanoparticles offer high catalytic activity but suffer from surface oxidation, aggregation, and limited aqueous stability. MOFs, though highly porous and selective, often require complex synthesis and exhibit structural instability in humid environments. Polymer sensors provide good flexibility yet lack precise control over electronic transitions essential for fluorescence-based quantification. In contrast, CQDs combine strong emission intensity, excitation-dependent tunability, facile green synthesis, and excellent dispersibility, making them particularly suited for organophosphate detection in real-world matrices.²³ Their heteroatom-doped and surface-passivated variants further enhance selectivity and limit matrix interference, offering a sustainable and reproducible platform for field-deployable sensing.

Globally, pesticide exposure continues to pose major occupational and environmental health challenges, especially in low- and middle-income countries with intensive agricultural practices. The World Health Organization estimates that hundreds of millions of people experience accidental or intentional pesticide poisoning annually, leading to more than 1 000 000 deaths^23–25 (Fig. 3). This persistent global burden underscores the urgent need for safer, sustainable detection platforms that can rapidly identify hazardous pesticide residues and metabolites in environmental and biological samples. Accordingly, this review focuses on biomass-derived CQDs as next-generation fluorescent nanosensors for organophosphate pesticides and their degradation products. It outlines recent developments in green synthesis, physicochemical characterization, fluorescence mechanisms, and detection strategies, emphasizing the challenges and future opportunities for CQD-based sensing in environmental and public-health applications.

Fig. 3 Statistics of pesticide-related mortality in India, along with a comparative representation of fatalities from other causes and the global impact of pesticide exposure.

2. Carbon quantum dots (CQDs): synthesis approach

Carbon quantum dots (CQDs) were first discovered quite accidentally during the purification process of single-walled carbon nanotubes (SWCNTs) from arc-discharged soot. Accordingly, numerous synthetic routes have been developed to achieve CQDs with defined functionality in terms of scalability, economic efficiency, tunability in particle size, and compositional diversity. The synthesis techniques can largely be divided into two broad approaches: top-down and bottom-up approaches.²⁶ The basic mechanisms of these two techniques are different; the top-down technique is dissolution of larger carbon materials, while the bottom-up technique builds CQDs from individual molecular precursors^27,28 (Fig. 4).

Fig. 4 Schematic illustration of top-down and bottom-up approaches for CQD synthesis, highlighting starting materials, processing methods, and relative advantages.

The top-down method is the breaking up of large carbonaceous material via processes such as chemical oxidation, discharge, electrochemical oxidation and ultrasonic methods. On the other hand, the bottom-up method develops smaller carbon structures into CQDs of the desired size. Common bottom-up methods including hydrothermal treatment, ultrasonic treatment, thermal decomposition, pyrolysis, carbonization, microwave synthesis and solvothermal methods are used for the synthesis of CQDs. The chemical difference between the two approaches is illustrated in Fig. 5, which shows how the top-down approach breaks the bulk material down to the CQDs whereas the bottom-up approach builds the material up from molecules.

Fig. 5 Detailed schematic of CQD synthesis: top-down method involving disintegration of bulk carbon materials; bottom-up method constructing CQDs from molecular precursors via ionization and molecular clustering.

Top-down methods generally result in particles or flakes of small size with a wide size distribution,²⁹ whereas bottom-up methods generally result in particles of uniform size, which is desirable in biomedical applications, but accuracy can be limited by using expensive methods such as lithography or focused ion beam.³⁰ So bottom-up synthesis is considered to be easier and more accurate in the synthesis of smaller nanoparticles below 100 nm while the top-down synthesis method is employed for the synthesis of thin films and larger nanoparticles above 100 nm.³¹ Importantly, the efficiency of heteroatom doping (N, S, P, B) in CQDs is highly dependent on the synthesis route. Bottom-up methods, due to their molecular-level assembly, allow precise incorporation of these dopants into the carbon lattice or on surface functional groups. Such doping directly influences the optical and electronic properties of CQDs, including quantum yield, emission wavelength, and defect states. In the context of pesticide detection, heteroatom doping enhances the photo-induced electron transfer (PET) from CQDs to electron-withdrawing analytes, modulates Förster resonance energy transfer (FRET) between CQDs and target molecules, and alters the inner filter effect (IFE) for improved sensitivity and selectivity toward organophosphate pesticides and nitroaromatic metabolites like p-nitrophenol (PNP). Consequently, the choice of synthesis route not only governs CQD structure and morphology but also determines their performance as highly selective fluorescent sensors.

While several top-down methods such as laser ablation, microwave irradiation, etc., have been used, they are associated with extreme reaction conditions, low product yield, poor particle size control, and use of toxic reagents or high energy input. Thus, the need for greener, safer and more sustainable synthetic protocols has become an absolute need, especially considering environmental concerns and global sustainability goals. Compared to bottom-up methodology, top-down approaches are usually limited by non-eco-friendly processes, impure products and poor yield. Conversely, bottom-up approaches are characterized by better size control and morphology, better yields, greener synthetic pathways, and exploration of abundant precursors. This difference directly translates to the final price, again in favor of bottom up approaches as the method of choice.³²

Bottom-up syntheses use relatively mild external energy inputs (e.g. ultra-sonication, microwave-assisted pyrolysis, hydrothermal heating) and are safer and more sustainable than top-down syntheses that use starting materials such as graphite powder or multi-walled carbon nanotubes (MWCNTs) under harsh physical/chemical conditions.³⁴ In addition, top-down derived CQDs usually exhibit shorter fluorescence emission peaks and poor size distribution and morphological control. On the other hand, bottom-up approaches allow the precise control of product performance, morphology, and surface functionalities by constructing suitable precursors or by assembling small building blocks.³⁵ The simplicity of heteroatom doping during the synthesis is another great advantage of the bottom-up approach and can be used to tune the electronic and optical properties of CQDs. The incorporation of heteroatoms (N, S, P, B) during bottom-up synthesis not only modifies the electronic structure of CQDs but also enhances their interaction with specific analytes. Nitrogen doping introduces additional lone-pair electrons that facilitate stronger PET interactions with phosphoryl groups in organophosphate pesticides, while sulfur or boron doping can improve binding to nitroaromatic metabolites like p-nitrophenol (PNP). Consequently, the choice of synthesis strategy directly determines the selectivity, sensitivity, and linearity of CQD-based fluorescence sensors.

In particular, among bottom-up techniques, hydrothermal and pyrolysis routes are of special interest as they provide high quantum yields, low cost and environmentally-friendly protocols. Most of these methods employ simple biomass residues (e.g. fruit peels or plant waste) as carbon sources, dissolved in water and treated in Teflon-lined autoclaves under controlled temperature and pressure conditions to customize CQD properties.³⁶ Even though the process is promising, there are challenges such as poor mixing in large reactors (autoclaves) and potential leakage during reaction which can be overcome through mechanical stirring or sealing challenges.³⁷ Despite the progress, CQD synthesis still suffers from the following drawbacks: (i) carbon aggregate formation during carbonization, quenching the fluorescence; (ii) the size control is difficult, and post-treatments such as dialysis or centrifugation are still necessary; and (iii) surface functionalization, which has a strong impact on solubility and biocompatibility.³⁸ Nevertheless, bottom-up techniques, particularly hydrothermal and biomass-based methods, are still the most promising ones because of their precision, reproducibility and environmental friendliness³⁹ (Table 2).

Although the physicochemical properties of CQDs are intrinsic to the synthesis method used, they are of particular relevance in the area of pesticide detection, particularly for organophosphate (OP) pesticides and their metabolites such as p-nitrophenol (PNP). Carbon quantum dots (CQDs) which are synthesized according to bottom-up green synthesis methods typically possess abundant hydroxyl and carboxylic groups on their surfaces. It is seen that these functional groups can participate in hydrogen bonding, electrostatic bonding, and p–p stacking with OP compounds or nitroaromatic metabolites like PNP, resulting in fluorescence quenching in the form of a quantitative analysis.⁴⁰ For example, CQDs prepared from hydrothermal treatment of citric acid or fruit peels show strong fluorescence which is highly sensitive to phosphoryl or nitro groups, and therefore is suitable for the detection of OP residues such as malathion or parathion and for the detection of PNP in biological fluids such as urine.⁴¹ Despite the advantages of biomass-derived CQDs, challenges remain in reproducibility and scalability. Variations in feedstock composition (e.g., cellulose, lignin, or protein content) can affect carbonization efficiency, surface functionalization, and ultimately fluorescence properties. Careful optimization of reaction conditions, including temperature, precursor concentration, and post-synthetic passivation, is essential to maintain batch-to-batch consistency. Such control is particularly critical for real-world sensing applications in complex matrices like water, soil, food, and biological fluids, where emission stability and resistance to matrix interference are paramount.

Moreover, doping mechanisms introduced in the synthesis process (i.e. N-doping, S-doping) enhance the efficiency of electron transfer between CQDs and pesticide molecules, which, consequently, enhances the detection sensitivity. For instance, nitrogen-doped CQDs are found to be more selective for phosphate and thiophosphate functional groups in OPs⁴² while sulphur or boron doping enhances the detection of nitro groups in PNP.⁴³ These design features demonstrate the importance of the synthesis strategy not only to prepare quality CQDs but also to make their optical and surface properties favourable for selective detection of organophosphates and their toxic metabolites. The performance of various CQD-based fluorescent sensors reported in recent literature is summarized in Table 1.

Table 1 Comparative summary of CQD-based sensors: mechanisms, detection limits, and sample applications

Sr. no.	Study/sensor type	Analyte(s)	Recognition type/sensor mechanism	Detection limit (LOD)	Sample matrix	Reproducibility/recovery	Ref. no.
1.	Orange pomace-derived CQDs	4-Nitrophenol, Cr^6+	N,S-co-doped CQDs; fluorescence quenching (IFE/PET)	∼14 nM (4-NP); ∼59.6 nM (Cr^6+)	Real water (lake, tap)	Recoveries 91.18–103.14%, RSD 0.3–2%	44
2.	CQDs@MIP sensor	Nitrofen pesticide	Molecularly imprinted polymer on CQDs	2.5 × 10–3 mg L^−1	Seawater, tap, purified water	Recoveries 84.1–115.7%, RSD ≤ 3.1–6.7% (different waters)	45
3.	S-doped CQD/AChE biosensor	Malathion, chlorpyrifos	Enzyme inhibition with S-doped CQDs + AChE + Cu^2+	∼1.7 ppb (malathion), ∼1.5 ppb (chlorpyrifos)	Buffer/spiked water	Good reproducibility in lab, RSDs not fully reported	46
4.	Carbon quantum dots (CQDs)-based FRET sensor	Organophosphate pesticide (paraoxon)	Fluorescence resonance energy transfer (FRET), inhibition of BChE by OPs reduces fluorescence recovery	0.05 μg L^−1	Tap water and river water	Repeatable and accurate	47
5.	Label-free fluorescent aptasensor based on CDs-AuNPs system	Kanamycin	Inner filter effect (IFE)	18 nM (0.018 μM)	Milk samples	Good applicability; validated in real milk samples	48
6.	Carbon quantum dots (CQDs)-based fluorescent sensor	Amoxicillin (AMO)	Fluorescence quenching of CQDs	0.475 μM	Not specified	Fast response, stable, highly sensitive and selective	49
7.	β-Cyclodextrin-modified N,Zn co-doped carbon dots (β-CD-N,Zn-CDs) fluorescent sensor	Fluoroquinolone derivatives (FQs) ofloxacin (OFL)	Fluorescence enhancement and red-shift	0.05 μM	Milk and domestic water	Satisfactory recoveries; reliable and accurate	50

---

Table 2 Comparison of key features, advantages, and limitations of top-down versus bottom-up

Sr. no.	Feature	Top-down approach	Bottom-up approach	Ref.
1.	Basic principle	Breaking down large carbon structures	Assembling small molecules into CQDs	35
2.	Starting materials	Graphite, soot, carbon nanotubes	Citric acid, glucose, biomass, amino acids	39
3.	Common methods	Laser ablation, chemical oxidation, electrochemical oxidation, ultrasonic	Hydrothermal, pyrolysis, microwave, Solvothermal	39
4.	Particle size control	Poor, wide distribution	Good, uniform and tuneable	35
5.	Product yield	Low	High	32
6.	Reaction conditions	Harsh (strong acids/bases, high energy)	Mild (water-based, moderate heat, eco-friendly)	33
7.	Quantum yield	Moderate to low	High (especially in hydrothermal/pyrolysis)	32
8.	Environmental impact	Less green, toxic reagents often used	Eco-friendly, greener processes	33
9.	Cost-effectiveness	Expensive (raw materials and setup)	Cost-effective (biomass and simple equipment)	39
10.	Advantages	Suitable for thin films or larger carbon-based materials	Tuneable, scalable, cleaner process, better fluorescence performance	35
11.	Disadvantages	Harsh conditions, low yield, toxic reagents	Requires careful temperature and time optimization	35

---

Moreover, the use of agricultural residues to form green synthesis pathways is a subset of the greater sustainable pesticide monitoring agenda. Since pesticide contamination in itself is an environmental hazard, using environmentally friendly substances to manufacture the detection material reduces the environmental hazard of the monitoring process itself. The choice of the synthesis technique in specific biomass-derived bottom-up procedures thus plays a dominant role in the design of CQD-based sensing platforms of organophosphate pesticides and p-nitrophenol towards practical applications. Overall, the synthesis approach is not merely a procedural choice but a design parameter that dictates the optical, electronic, and surface characteristics of CQDs. By selecting suitable precursors, energy inputs, and doping strategies, researchers can tailor CQDs for specific detection tasks, ensuring high sensitivity, matrix tolerance, and compatibility with practical sensing platforms for organophosphate pesticides and their toxic metabolites.

3. Optical and structural properties of CQDs – absorbance, fluorescence, photoluminescence & phosphorescence

3.1. Chemical structure

Carbon quantum dots (CQDs) typically consist of a graphitic/partially graphitized core as well as various surface functional groups. The core consists largely of sp² -hybridized carbon domains that do not take place in long-range aromatic structures such as in graphene or polyaromatic hydrocarbons.⁵¹ However, based on the synthesis pathway, the core may consist of crystalline and amorphous parts, and the degree of crystallinity can influence optical and electronic characteristics of the CQDs.⁵² Above this carbon-rich core is a shell constructed of surface functional groups, typically added in the course of synthesis or in a separate post-synthetic modification. Commonly these groups include: hydroxyl (–OH), carboxyl (–COOH), carbonyl (C=O), epoxide (C–O–C), amine and amide (–NH₂, –CONH₂) groups⁵³ (Fig. 7). The surface groups enhance the water solubility, stability and chemical reactivity of CQDs and play a role in controlling photoluminescence, surface charge and biocompatibility. They also may serve as platforms to be further functionalized or doped to obtain the desired CQD properties.⁵⁴ Importantly, the nature and density of these surface groups do not just influence solubility and biocompatibility, but also modulate the electronic transitions responsible for photoluminescence. For instance, nitrogen-doping introduces electron-rich sites that can enhance radiative recombination, whereas sulfur or phosphorus doping can create mid-gap states that tune emission wavelengths and quantum yields. This indicates a direct link between chemical structure and sensing performance, as these modifications affect interactions with electron-withdrawing analytes such as organophosphate pesticides and p-nitrophenol. At the structural level, CQDs are carbogenic whose core is composed of an amorphous and crystalline environment, and are surrounded by surface functional groups. Although the vast majority of the studies confirm the presence of crystalline sp² carbon regions, CQDs are generally less crystalline and have more defects compared to GQDs,⁵⁵ which are characterized by well-ordered graphene lattices. Both CQDs and GQDs are, however, capped with oxygen-containing groups, and thus GQDs can be called a subclass of CQDs.⁵⁶ The degree of crystallinity and defect density in the core strongly affects exciton migration and non-radiative decay pathways. Highly defective or amorphous CQDs often show broad, excitation-dependent emission, which can be advantageous for multiplexed sensing but may reduce reproducibility unless surface passivation or controlled doping is employed.

A variety of structural models for the CQD core have been suggested, including diamond-like, graphite/graphite oxide and amorphous carbon structures. Such diversity is confirmed by electron microscopy and spectroscopy: CQDs fabricated using laser ablation and PEG passivation exhibit SAED patterns consistent with diamond-like planes, and electrochemically etched carbon fibres exhibit lattice spacings of ∼0.325 nm consistent with graphite (002) facets.^57–59 On the other hand, hydrothermally prepared CQDs are reported to be amorphous with no discernible lattice fringes, and their XRD patterns have broad peaks at about 25 deg (0.34 nm), characteristic of highly disordered carbon.^59,60

Surface functional groups are found to be important to the properties of CQDs. For instance, multicolour fluorescent CQDs enriched with –OH and –COOH groups were obtained through the oxidative acid treatment of candle soot.⁶¹ Elemental analysis confirms that there is an increase in oxygen content compared with raw soot, which is mainly due to the presence of carbonyl functionalities. Furthermore, the FTIR and XPS measurements show that hydroxyl, carbonyl, and carboxyl groups are inevitably present on CQD surfaces.⁶² In addition, GQDs prepared by microwave-assisted methods exhibit strong FTIR bands of C–O (1027, 1076 cm⁻¹) and O–H stretching (1360 & 2927 cm⁻¹), which is confirmed by XPS (Fig. 6).⁶³

Fig. 6 Schematic representation of carbon quantum dots (CQDs) showing their carbogenic core (sp²-hybridized carbon domains) and different surface functional groups that modulate solubility, photoluminescence, and reactivity.

3.2. Electronic structure

The electronic structure of carbon quantum dots (CQDs) has been studied extensively, and it is generally described by molecular orbital (MO) theory. In this theory, the photoluminescence and absorption properties of CQDs are attributed to electronic transitions that are primarily n–p and p–p transitions, which are energetically favoured because of the unique hybridization and surface chemistry of CQDs.⁶⁴

3.2.1 π-states and aromatic sp² regions. The p-states in CQDs are induced by the aromatic sp²-hybridized carbon atoms of the graphitic or partially conjugated domains of the CQD core. These domains can be viewed as being small polyaromatic hydrocarbons (PAHs), and, as in these molecules, the degree of p-conjugation has a strong effect on the energy gap between the HOMO (p) and LUMO (p) levels. Experiments have shown that the p–p energy gap decreases and the absorption and emission red-shift with increases in the number of fused aromatic systems, which is a similar trend to conventional organic conjugated systems.⁶⁵ The electronic states of CQDs are mainly the hyper conjugation between p-states derived from aromatic sp² domains and n-states derived from surface functional groups, as shown in Fig. 7. Moreover, the electronic states of CQDs are significantly modulated by heteroatom incorporation. Nitrogen-doped sp² domains tend to lower the HOMO–LUMO gap, producing red-shifted emission, whereas oxygen or sulfur-containing functional groups can introduce localized n-states that act as quenching or energy transfer sites. This interplay directly influences fluorescence-based sensing mechanisms such as PET, IFE, and FRET, demonstrating how chemical modification and electronic structure are inseparably linked.

Fig. 7 Electronic states and transitions in CQDs: (a) π → π transitions from aromatic sp² regions, (b) n → π* transitions arising from surface functional groups, and (c) size- and surface-dependent quantum confinement effects influencing emission.

3.2.2 n-states and surface functional groups. Apart from p-states, CQDs also exhibit n-states, caused by non-bonding electron pairs (lone pairs) of heteroatoms (oxygen, nitrogen and sulphur) on surface functional groups. Common origins of these non-bonding orbitals include functional moieties like carbonyl (C=O), amine (NH₂), amide (CONH₂) and thiol (SH). When covalently bound to aromatic sp² carbons, these groups induce the n → p transitions.⁶⁶ Such transitions are also of special interest in the interpretation of the ultraviolet-visible (UV-vis) absorption spectra of CQDs, where broad absorption bands are typically assigned to n → p transition of surface-bound carbonyls/carboxylic acids, and p → p transition of the core^67–69 (Fig. 7).

3.2.3 Size- and surface-dependent electronic behaviour. Besides, the electronic structure of CQDs is also dominated by the quantum confinement effect. With the decrease of the size of the sp²-conjugated domain (i.e., the CQD size), the energy gap becomes larger and blue-shifted emission takes place.⁷⁰ Larger aromatic domains enable larger p-delocalization which results in smaller band gaps and red-shifted emission.⁷¹ Moreover, new electronic states or changes in the electronic states (energy levels) can be introduced by chemical doping (with sulphur or nitrogen, for example) or surface passivation^72,73 and this influences not only the emission but also the absorption optical properties of CQDs. The properties of such systems are of great importance for the detection of pesticides, as the external analytes perturb the CQDs' excited state transitions. As a result of the electron-withdrawing properties of the phosphoryl groups and the nitro groups in organophosphates and p-nitrophenol, respectively, they both affect the electronic states of CQDs through photo-induced electron transfer (PET), static quenching, and the inner filter effect (IFE) (Fig. 8).^74,75 The interactions generate measurable quenching of fluorescence or spectral position shifts that can be quantitatively correlated to analyte concentration. To illustrate this, PNP on parathion is an effective CQD fluorescence quencher through electron transfer between the nitro aromatic moiety and the excited CQD states⁷⁶ and can serve as a convenient biomarker, which is measurable in a urine sample that is as small as a drop. In addition, CQDs containing a heteroatom have been detected with high orientation to OP pesticides and with higher detection limits of nitro aromatic metabolites increased to the nano molar range.⁷⁷ Critically, surface chemistry and size-dependent electronic behavior are not merely theoretical curiosities; they define real-world sensor performance. For example, smaller CQDs with larger band gaps exhibit blue-shifted emission and faster response to analytes, while surface defects or doping can enhance selectivity toward electron-deficient species. Understanding these relationships is crucial for designing sensors with optimized sensitivity and reproducibility.

Fig. 8 Overview of the optical properties of CQDs: broad absorbance due to π–π and n–π* transitions, strong tunable fluorescence and photoluminescence, and possible long-lived phosphorescence under suitable conditions.

Thus, the combination of the chemical structure, electronic states and surface chemistry of CQDs determines not only the intrinsic photo physics of CQDs but also establishes the molecular basis of their application to the detection of toxic organophosphate pesticides and their harmful products of degradation.

3.3. Optical properties of carbon quantum dots

Carbon quantum dots (CQDs) are unique optical emitters whose unusual optical characteristics are the basis of their application in sensing, imaging, catalysis, and optoelectronics. The quantum-confined carbogenic core, abundant surface states, and multifunctional functional groups bring about unique properties in terms of absorbance, fluorescence, photoluminescence and phosphorescence.⁷⁸Fig. 8 has a summary of these optical phenomena, absorbance, fluorescence and phosphorescence. These optical properties are particularly pertinent to pesticide detection: the interaction of CQDs with organophosphate (OP) pesticide or its metabolites, such as p-nitrophenol (PNP), directly alters their emission spectra, and can therefore be detectable selectively and sensitively.

3.3.1 Absorbance properties. CQDs have wide ultraviolet-visible (UV-vis) absorption spectra in which the characteristic peaks are generally ascribed to π to pi transitions of aromatic sp² moieties and n to 0 transitions of the functional groups on the surface, including carbonyls or carboxylates. The most frequently used absorption peaks are between 250–350 nm with red-shifts potentially being possible depending on passivation as well as heteroatom doping of the surface.⁷⁹ The pesticides can be detected by the absorbance changes. The interaction of CQD excited states with the electron-withdrawing groups of OPs and PNP is strong. As one example, PNP in the form of a double salt exhibits an average absorption peak at 400 nm, which coincides with the CQD emission spectra. This overlap results in an inner filter effect (IFE), in which CQD excitation or emission light is absorbed by PNP and leads to fluorescence quenching. Thus, pesticide residues and metabolites can be detected by the simplest and faster means of observing their absorbance changes.⁸⁰ Heteroatom doping can also cause systematic red- or blue-shifts in absorption peaks, which allows tuning of the spectral overlap with specific analytes. This tunability is particularly valuable for inner filter effect-based sensing, as it can maximize the overlap between CQD emission and the absorption spectrum of pesticides or their metabolites, thereby improving detection limits.

3.3.2 Fluorescence and photoluminescence. CQDs have the strongest and tuneable fluorescence as their most typical feature. They have an excitation-dependent PL, and consequently tend to have multicolour emissions by radiative recombination of surface defect states, molecular states or π-domains of the carbon core.⁸¹ CQDs have emission in the entire visible range, and quantum yields can be readily enhanced by the addition of nitrogen or sulphur, which are also dopants.⁸² During fluorescence sensing, the fluorescence of CQDs is suppressed or enhanced upon a collision with the analytes.⁸³ Photoinduced electron transfer, where the phosphoryl group is an electron acceptor of the excited CQD, is most commonly the cause of PET-based quenching with OP pesticides. With PNP, the nitroaromatic moiety is a very potent electron-withdrawing center leading to strong quenching of fluorescence of CQDs by PET. This quenching is directly proportional to PNP concentration and can be determined quantitatively in both biological fluids such as urine and in environmental matrices such as wastewater.⁸⁴ Furthermore, defect engineering whether via controlled oxidation or heteroatom incorporation enhances quantum yield and photostability, both of which are critical for reproducible sensing in real matrices. The combined effects of doping and surface passivation modulate PET efficiency and determine whether fluorescence quenching will be dominated by static, dynamic, or combined mechanisms.

3.3.3 Phosphorescence and long-lived emission. This is a less common phenomenon, but CQDs can also be found to display room-temperature phosphorescence when they are either functionalized or embedded within solid matrices.⁸⁵ It is a long-lived emission which can be explained by intersystem crossing (ISC) between singlet and triplet emission due to the heavy-atomic effect or heteroatomic doping⁸⁶ (Fig. 8). The advantage of phosphorescence-based sensing is an absence of background fluorescence interference, thereby increasing sensitivity. Phosphorescent CQDs may provide time-resolved sensing platforms to resolve pesticide signals among other naturally fluorescent organic molecules in complex samples to detect OP.⁸⁷ While phosphorescent CQDs are less common, their long-lived emission provides an additional advantage for time-resolved sensing in complex samples where background autofluorescence may interfere. This illustrates the importance of tailoring both core structure and surface chemistry to match specific sensing contexts, highlighting the link between optical properties, structural defects, and analytical utility.

3.4. Scalability and reproducibility challenges of biomass-derived CQDs

While biomass-derived CQDs are environmentally friendly and affordable, scalability continues to be hampered by intrinsic variability in the composition of the precursor feedstocks (e.g., cellulose to lignin to protein to carbohydrate ratios). Such variability in composition causes batch-to-batch variations in the carbonization degree, heteroatom doping, and defect density, and then affects the optical characteristics such as fluorescence quantum yield, emission wavelength, and photostability.^73–75 Moreover, non-uniformity in the absence of standardized synthesis conditions like temperature, pH, and precursor concentration also exacerbates reproducibility across labs. As such, the same biomass precursor can produce CQDs with distinct emission characteristics as well as sensing responses.⁸⁵ From a practical perspective, these structural and optical variabilities directly influence sensor performance. Variations in quantum yield, emission wavelength, and surface reactivity can lead to inconsistencies in analyte detection, particularly in complex matrices such as soil, fruit washes, or biological fluids. Therefore, reproducibility is not only a synthetic concern but also a critical determinant of sensor reliability. Systematic optimization as well as feedstock standardization is necessary to reach industrial-scale production to ensure reproducible structural as well as optical behaviour. Scalable synthesis pathways, i.e., continuous-flow hydrothermal or microwave-assisted routes, can help to circumvent such issues to control the process as well as reproduce it with integrity, yet still adhere to the principles of green synthesis. Additionally, standardization of heteroatom doping and defect densities is necessary to ensure that desired optical and electronic properties are consistently achieved. Without such control, the relationship between CQD structure and sensing mechanism may be unpredictable, undermining both laboratory validation and field deployment.

4. Defects of CQDs: significance in detection

Carbon quantum dots (CQDs), no matter the synthesis route employed, contain a host of structural and surface defects naturally. These flaws have severe impacts on their optical, electronic, and chemical behaviours which, in most cases, become the key distinguishing factors between CQDs and other carbon nanomaterials such as graphene quantum dots (GQDs). Lattice vacancies, edge defects and disordered regions of carbon⁸⁸ are the most frequent structural defects, but oxygen-containing functional groups such as hydroxyl (–OH), carbonyl (C=O) and carboxyl (–COOH) groups are typical surface defects. These groups break the sp²-hybridized conjugated network by introducing localized sp³-hybridized carbon atoms, and thus cause the defect-rich character of CQDs.⁸⁹ Experimental characterizations substantiate the defect-rich structure of CQDs. X-ray diffraction (XRD) patterns typically exhibit broad peaks typical of amorphous carbon, and Raman spectroscopy exhibits high I_D/I_G ratios, indicating higher disorder and greater defect concentration.⁹⁰ This disorder can decrease crystallinity relative to graphene-based structures, but at the same time, provides new avenues for designing the material's functionality. Defects are not just structural flaws; they are dynamic players in the photophysics of CQDs. Defect locations sometimes act as exciton trapping sites which adds extra energy levels that helps in surface-state-governed photoluminescence (PL).⁹¹

Surface states are alternative radiative recombination channels, resulting in increased emission intensity, excitation-dependent fluorescence that is adjustable and better quantum yield.⁹² Additionally, defect engineering via controlled oxidation, heteroatom doping, or surface passivation allows for the accurate modulation of absorption/emission characteristics and charge-transfer efficiency, rendering CQDs platform-like materials for optical applications.⁹³ Defects play a more crucial role than optical modulation. Defect-associated surface groups enhance analyte binding and signal transduction in sensing applications. Carboxyl and hydroxyl functional groups at defect sites may potentially interact strongly with pesticides, heavy metals, and biomolecules, promoting sensitivity and selectivity.⁹⁴ Defect sites serve as electron transfer centres in catalysis and redox reactions, enhancing the kinetics of reaction. Additionally, the availability of –COOH, –OH, or –NH₂ groups at defect sites allows for easy post-synthetic functionalization and extends the applications of CQDs in bioconjugation, imaging, and drug delivery.⁹⁵ Therefore, defects show multi-functionality rather than just being considered as only flaws. For pesticide detection, defect engineering is a critical factor.⁹⁶ Surface oxygenated groups formed on defect sites not only enhance water solubility and dispersion but also allow for good hydrogen bonding and electrostatic interactions with organophosphate (OP) pesticides and their toxic degradation products like p-nitrophenol (PNP).⁹⁷ These interactions favor effective charge transfer and fluorescence quenching via mechanisms like the inner filter effect (IFE) and photoinduced electron transfer (PET). For example, the nitro group in PNP and the phosphoryl group in OPs are both good electron acceptors, which interact with defect-rich CQDs to generate detectable photoluminescence changes.⁹⁸ Therefore, CQDs with defects are the best sensors to detect pesticide residues in environmental and biological samples. Therefore, what would be considered as defects in CQDs are positive features that make CQDs the best in environmental monitoring and biosensing. CQDs could be customized by defect density and type to serve as green and highly efficient pesticide detectors in complex environments and biological matrices.

Defects in CQDs are not only responsible for enhanced photoluminescence but also dictate the primary mechanisms of analyte detection. Surface and edge defects act as active sites for charge transfer interactions, facilitating PET, static quenching, and IFE with pesticide molecules. In particular, the spatial distribution and chemical nature of defects determine how efficiently electrons or energy are transferred between CQDs and analytes. For example, edge defects with hydroxyl or carboxyl groups can stabilize binding of phosphoryl groups in organophosphates, promoting strong fluorescence quenching. Similarly, dopant-induced defects can adjust the energy level alignment between the CQD and the analyte, enabling more efficient Förster resonance energy transfer (FRET) for ratiometric sensing approaches. This mechanistic understanding connects structural defects directly to measurable optical responses, moving beyond purely descriptive characterization. While defect-rich CQDs show superior sensitivity, their performance can be affected by batch-to-batch variability in defect density and dopant incorporation. Standardizing synthesis protocols and precisely controlling reaction conditions, such as temperature, precursor ratio, and dopant concentration, is essential for reproducible sensing performance. Moreover, real-world matrices such as water, soil, fruit extracts, or urine introduce additional variables, including ionic strength, pH fluctuations, and competing organic molecules. Carefully engineered defect sites, combined with heteroatom doping, can improve matrix tolerance by enhancing selective analyte binding and stabilizing fluorescence signals. Such strategies ensure that defect-engineered CQDs maintain their high sensitivity and selectivity in practical environmental and biological monitoring applications.

Future research in CQD defect engineering should focus on rational design of defect types and densities tailored to specific sensing targets. For example, multi-dopant strategies or post-synthetic surface functionalization could optimize both quantum yield and analyte selectivity. Additionally, integrating defect-engineered CQDs into hybrid platforms, such as CQD-metal oxide composites or electrochemical sensors, could further enhance signal amplification and robustness. Advanced characterization techniques, such as time-resolved spectroscopy and high-resolution electron microscopy, will help to correlate specific defect features with sensing efficiency. Ultimately, a mechanistic understanding of how defects influence photophysics and analyte interactions will enable the design of next-generation, reproducible, and field-deployable CQD-based sensors for environmental and human health applications.

5. Sensing strategies and the principles of detection

Photoluminescence of CQDs is extremely sensitive to the chemical environment around it, and therefore there are multiple sensing principles to use for pesticide detection. In principle, any variation of fluorescence intensity, wavelength, anisotropy or lifetime that is systematically dependent on analyte concentration can be used as a signal transduction technique.⁹⁹ Of these, fluorescence quenching, energy transfer processes and charge transfer are most important.

5.1. Fluorescence quenching

Fluorescence quenching has been studied extensively, both in general, and for its application to biochemical problems using fluorescence. Fluorescence quenching is defined as the decrease of the fluorescence intensity of CQDs mediated by the interaction with analytes (in this case, pesticides). This quenching may be accomplished by various mechanisms, which are distinguished mainly as dynamic quenching and static quenching,¹⁰⁰ both of which are applicable to pesticide analysis depending on the type of interaction. Both static and dynamic quenching require a contact between the quencher and fluorophore on the molecular level. The efficiency of these fluorescence-based sensing mechanisms is strongly influenced by the structural and chemical characteristics of the CQDs. Size, defect density, and surface functional groups dictate the accessibility of analytes to the fluorophore and modulate electron transfer rates. Heteroatom doping, such as nitrogen, sulfur, phosphorus, or boron, further tunes the electronic energy levels of CQDs, enhancing interactions with electron-accepting pesticides like p-nitrophenol or organophosphates. For instance, nitrogen-doped CQDs have been shown to increase PET efficiency due to elevated electron density, while sulfur or phosphorus doping can modify HOMO–LUMO gaps, thereby altering FRET and IFE sensitivity. Similarly, defect-rich CQDs provide additional surface states that act as trap sites, facilitating charge transfer and enhancing fluorescence quenching.

5.2. Static and dynamic (collisional) quenching

Fluorescence quenching refers to a phenomenon that reduces the total intensity of fluorescent light. In collisional quenching, the quencher has to diffuse to the excited state fluorophore during the excited state lifetime. When the fluorophore is hit, the fluorophore reverts to the ground state, without emitting a photon. In static quenching a complex is formed between the fluorophore and the quencher and this complex is non-fluorescent (Fig. 9).¹⁰¹ In either case, the quencher and fluorophore must be in contact with each other. It is this key need which leads to the many uses of quenching. Dynamic quenching requires that the quencher is near the fluorescent molecule in its excited state, and then a reaction takes place that speeds up the decay of the excited state. This results in a shorter fluorescence lifetime and does not affect the absorption spectrum. For instance, the quenching measurements can provide the information about the accessibility of the fluorophore to quenchers. If the solvent is very viscous then diffusion is slow and quenching is prevented. Hence, quenching can be used to measure the diffusivity of quenchers. These quenching mechanisms are exploited for sensing OPs like malathion, parathion, and chlorpyrifos.^102,103 Furthermore, consider a fluorophore that is bound to a protein (or a membrane). If the protein/membrane is impermeable to the quencher and the fluorophore is in the interior of the macromolecule, then neither collisional nor static quenching is possible. For this reason, quenching studies can be used to give insight into the localization of fluorophores in proteins and membranes, and their permeability to quenchers.

Fig. 9 Schematic representation of static quenching, where the fluorophore forms a non-fluorescent ground-state complex with the quencher, resulting in reduced emission intensity.

a. Photoinduced electron transfer (PET). PET is a quenching mechanism that is based on an intramolecular redox reaction between the excited state of the fluorophore and another end group that is able to donate or accept an electron. In PET the electron donor and the electron acceptor form a large complex.¹⁰⁴ The complex has been shown to return to the ground state without emission of a photon, although in some cases exciplex emission can be observed. In the end, the extra electron on the acceptor is transferred back to the electron donor to finish the reaction (Fig. 10).¹⁰⁵

Fig. 10 Schematic illustration of photo-induced electron transfer (PET), where excitation of the donor molecule leads to electron transfer to the acceptor, resulting in fluorescence quenching or altered emission properties.

b. Photo-induced charge transfer (PCT). This process involves transfer of an electron between the electron donor and acceptor functionalities to induce FL. Partial charge transfer sensors are based on partial transfer of charges in a fully conjugated system.¹⁰⁶ The interaction between the donor and acceptor produces a change of electron energy levels, which causes changes in FL signals.¹⁰⁷ One difference between the two sensors is that sensors have an integrated receptor and fluorophore, while PET sensors have the electron donor moiety separated from the fluorophore through a spacer (Fig. 11).

Fig. 11 Schematic representation of photo-induced charge transfer (PICT), in which photo-excitation promotes charge separation between donor and acceptor species, facilitating electron-hole transfer and influencing optical/electronic properties.

c. Internal filter effect (IFE). IFE depends on the spectral overlap between the fluorescent dye (the fluorophore) and the absorbing molecule (the absorber). Unlike FRET, IFE uses radiative energy transfer, and mainly affects the ground state of the donor by energy perturbation.¹⁰⁸ Hence, IFE only leads to fluorescence quenching without a noticeable change in the fluorescence lifetime. Another remarkable difference with FRET is that there is no distance requirement between the energy donor and the energy absorber in IFE.¹⁰⁹

While each mechanism provides a distinct sensing modality, they vary in practical efficiency and limitations. PET offers high sensitivity to electron-withdrawing analytes but may be affected by competing fluorophores in complex matrices. FRET enables ratiometric sensing and improves robustness against intensity fluctuations but requires precise donor–acceptor alignment and proximity within 1–10 nm. IFE is simple and robust, yet relies heavily on spectral overlap and can be limited at very low analyte concentrations. AIE phenomena provide enhanced emission in aggregated or solid states, making them suitable for immobilized sensor films, but are less effective in dilute aqueous environments. Understanding these nuances allows for rational selection or combination of mechanisms to optimize sensing performance under specific conditions.

d. Aggregation induced emission (AIE). AIE is a light emission phenomenon which is opposite to the aggregation-caused quenching (ACQ) effect. In AIE materials, the light emission is not in a strong fluorescence, but very low solution concentration is observed at higher loading or in the solid form.¹¹⁰ This behaviour originates from the dynamic intramolecular rotation of molecules in a dilute solution, which dissipates the energy of the excited state. However, in the aggregated state the intra molecular rotation is greatly restricted leading to non-radiative energy dissipation inhibition and the enhancement of FL.¹¹¹

e. Förster resonance energy transfer (FRET). Resonance energy transfer is also a useful phenomenon for fluorescence sensors. FRET is an in vitro technique where the excitation of an initially excited molecule (donor) returns to the ground state orbital with energy transfer of the electron on the acceptor.¹¹² In this process, non-radiative energy transfer between the donor and acceptor fluorophore called FRET pairs takes place when the emission spectrum of CDs overlaps with the absorption spectrum of the quencher, FRET proceeds without emission of photons due to long-range dipole–dipole interactions between CDs and the quencher.¹¹³ The efficacy of energy transfer depends on the relative orientation of donor and acceptor dipoles, overlap of the fluorescence emission spectrum of the donor with the absorption spectrum of the acceptor and the spatial separation between them. FRET occurs when the spectral crossover between the emission spectrum of the donor and the absorption spectrum of the acceptor exceeds 30% and the distance is less than 10 nm. By observing the change in the fluorescence intensity or lifetime of the donor carbon dot, one can sense the presence or concentration of the acceptor molecule and hence can be used in sensing applications sensitively.¹¹⁴ Carbon dots are preferred for FRET studies because they combine size tunable fluorescence properties, high photostability and biocompatibility, which allow for their use in a variety of sensing platforms.¹¹⁵

The above mechanisms are not just theoretical in nature, but have direct utility in sensing organophosphate pesticides and their derivatives. Organophosphates (malathion, parathion, and chlorpyrifos) undergo main interactions with CQDs by static quenching (SQ), PET, and IFE, due to their electron-withdrawing phosphoryl and ester groups. These interactions quench CQD excited states and dampen the fluorescence, thereby offering a simple and sensitive detection signal.¹¹⁶ In practical applications, matrix components such as dissolved organic matter, pigments, ions, and proteins can influence fluorescence quenching and energy transfer processes. Surface functionalization and heteroatom doping play a critical role in mitigating these interferences. For example, nitrogen- or sulfur-doped CQDs have demonstrated stable PET efficiency in environmental water samples, while defect-engineered CQDs maintain FRET signal fidelity in biological fluids like urine. Such structural modifications not only preserve the intrinsic optical properties but also enhance selectivity and reproducibility of pesticide detection in complex matrices.

p-Nitrophenol, one of the major parathion and methyl parathion degradation products, is especially suitable for CQD-based detection, because it has a strong electron-withdrawing nitro group and a unique absorbance in the visible region (∼400 nm under alkaline conditions).¹¹⁷ It is able to cause fluorescence quenching of CQDs via PET and IFE, so it is highly detectable even at trace concentrations in environmental and biological samples. Importantly, urinary p-nitrophenol has been identified as an indicator of human exposure to organophosphates and CQD-based fluorescence sensing provides a rapid, cost-effective and portable method of biomonitoring.¹¹⁸ CQD sensing strategies, based on the interaction of quenching and energy/charge transfer mechanisms, are promising tools for organophosphate pesticide detection and their metabolites. The versatility and sensitivity of these nanomaterials for real-world applications is attributed to the ability to exploit multiple quenching mechanisms, including static and dynamic quenching, PET, IFE, and FRET.

A comparative analysis of these sensing strategies suggests that no single mechanism is universally optimal. PET and IFE are highly sensitive for electron-withdrawing analytes; FRET offers ratiometric advantages and robustness to turbidity, while AIE is suitable for solid-state or immobilized sensing formats. Future research should focus on rationally designing doped and defect-engineered CQDs to exploit multiple mechanisms synergistically. Integration with portable platforms such as smartphone-based readouts or lateral-flow assays can provide rapid, field-deployable detection of organophosphates and metabolites, while maintaining accuracy and reproducibility across variable environmental and biological matrices.

6. Applications in pesticide detection: water, soil, food matrices, and human biomonitoring

The carbon-quantum-dot (CQD) platform has developed from a proof-of-concept fluorophore to effective matrix-insensitive sensors for organophosphate pesticide monitoring (i.e. malathion, parathion, and chlorpyrifos). One of their toxic nitroaromatic metabolite is p-nitrophenol. Nitrogen- or heteroatom-doped CQDs are responsive to molecular binding events in aqueous environments such as agricultural run-off, and the resulting fluorescence signatures can be quantitatively and stably translated into photo-induced electron transfer (PET), inner-filter effect (IFE), or Forster resonance energy transfer (FRET) signals. Notably, these optical readouts are competitive with reference chromatographic methods for most applications but at a considerably reduced instrumentation load and turnaround. LODs for OPs have been reported down to the sub-ppb to low-nM range, have been successfully recovered in difficult matrices (natural water, fruit exudate) with recovery levels in the range of 90–100%, and can be used for field screening and rapid triaging of risks.¹¹⁹ While CQDs exhibit excellent sensitivity under controlled laboratory conditions, real-world matrices present significant challenges including competing fluorophores, variable ionic strength, and adsorption onto natural organic matter. Understanding how surface functionalization, heteroatom doping, and defect density influence these interactions is essential for designing robust and selective sensors suitable for practical deployment.

6.1. Water

In ground and surface waters which are contaminated by pesticide applications, CQD probes are typically employed as dispersed nanosensors (flow-through/cuvette modes) or as immobilized films on supports or electrodes. Two mutually complementary sensing systems, one optical CQD assay with a LOD of about 1.70 ppb (about 5.1 nM), based on fluorescence quenching,¹²⁰ and the other electrochemical graphene-quantum-dot (GQD) glassy-carbon electrode, based on differential pulse voltammetry with a much lower LOD of about 0.62 nM,¹²¹ are presented to show the versatility and tolerance of the sensor. The former benefits from improved interfacial electron transfer and selective pre-concentration on the nanocarbon surface, while the latter offers equipment-minimal operation that is suitable for field screening; in both cases, both the linearity of calibration and detection range extend into the low-nM to micro-molar range of interest to environmental monitoring.¹²² Water matrices generally exhibit less interference with respect to soil or food, yet variable ionic strength, dissolved organic material, and co-exiting metal ions, can still interfere with quenching efficacy. CQDs, especially doped counterparts, suppress these interferences with the help of surface control and functionalization, such that selective binding is possible along with fluorescence stability under challenging aqueous conditions. The efficiency of PET, FRET, and IFE in water is modulated by CQD surface chemistry. Nitrogen doping, for example, increases electron density on the CQD surface, facilitating PET to electron-withdrawing pesticides, while sulfur doping can fine-tune energy levels for more efficient FRET. Nevertheless, natural organic matter and residual ions can still partially compete for binding sites, causing variability in fluorescence quenching. Batch-to-batch reproducibility of CQDs must be ensured through standardized synthesis and surface functionalization protocols to maintain sensor reliability Despite their high sensitivity in controlled aqueous environments, real water samples often contain humic substances, competing ions, and other fluorophores, which can partially suppress fluorescence quenching. Proper surface functionalization and doping (N, S, B) mitigate these effects but do not entirely eliminate matrix-induced variability.

6.2. Soil

More significant matrix effects arise from adsorption onto humics substances and mineral surfaces, variable ionic strength, and the presence of endogenous fluorophore.¹²³ CQD techniques therefore commonly couple a gentle extraction (e.g., buffered aqueous ethanol) with either optical readout in the supernatant or electro-analytical interrogation after drop-casting onto disposable electrodes. Heteroatom (N, S, B)-doped CQDs are advantageous as their surface functional groups (negatively charged –COOH/negatively charged –OH/negatively charged –NH₂) regulate p–p and hydrogen bonding interactions with OPs without compromising their high quantum yields in mildly coloured extracts.¹²⁴ In our review syntheses (2019–2024) we argue that this functionalization is no gimmick; it systematically perturbs the PET/IFE equilibrium and helps preserve linearity and selectivity even in the presence of soil-derived interferents.¹²⁵ Where reference testing has been performed, CQD estimates in soil eluates generally agree with GC-MS/HPLC to +−10–15%.¹²⁶ Compared to water samples, soil needs further pre-treatment due to strong suppression of the direct optical signal by humic matter and mineral binding, which is the major hindering factor for direct detection, thus making doped CQDs and extraction steps imperative.¹²⁷ Matrix effects in soil are one of the most challenging because of high levels of organic matter as well as variable mineralogy. Non-specific adsorption and light scattering in soil matrices can dampen fluorescence signals, making selective detection of organophosphates more difficult. Heteroatom-doped CQDs (N, S, B) enhance selective binding and electron transfer to target OPs, helping maintain linearity and selectivity even in humic-rich soils. Additionally, defect engineering and optimized surface chemistry are critical to counteract matrix-induced optical interference. However, reproducibility across soils with different mineralogies and organic content remains a key limitation, emphasizing the need for matrix-matched calibration. CQDs tackle such challenges with specific surface chemistry as well as hybridization with metal oxides/polymers that minimize non-specific adsorption as well as improve dispersibility. Total removal of background interference is still challenging, and additional optimization of the extraction/solid-phase pre concentration step is required to achieve consistent in situ sensing. Heteroatom-doped CQDs (N, S, B) exhibit enhanced binding and electron transfer to target organophosphates, helping to preserve fluorescence linearity and selectivity even in humic-rich soils. Defect engineering and surface chemistry optimization are thus crucial to maintain reliable detection in strongly adsorbing or optically interfering matrices.

6.3. Fruits and vegetables

Food matrices containing pigments, sugars and organic acids are a stress test for optical sensors. We have used two design approaches that have proven to be effective. First, CQDs embedded in paper or on a film-based immobilizer limit the re-absorption and accelerate surface swabbing of peels and cut surfaces;¹²⁸ second, smartphone-based readouts normalize the illumination and colorimetric and support semi-quantitative decisions in the field.¹²⁹ Although most demonstrations are based on a range of classes of pesticides, OPs are widely used as model analytes and nitrophenol as a convenient positive control for quenching behaviour. For example, smartphone-read CQD assays have quantified pesticide residues on fruits/vegetables at a minute-scale response,¹³⁰ and paper-supported green CDs have offered high sensitivity to nitrophenol under ambient conditions as well as showing that low-cost, portable, and training-light implementations are feasible for routine produce screening. Compared to water and soil, fruit and vegetable matrices have high background from endogenous pigments and sugars, thus, the use of immobilized CQD films and smartphone normalization are important to suppress optical interferences and allow portable screening. Optical interference from pigments, sugars, and irregular surface textures can bias fluorescence readouts. Ratiometric dual-emission strategies or immobilized CQD films help correct for such distortions. Continuous-flow or microwave-assisted CQD synthesis, along with standardized functionalization, improves batch-to-batch reproducibility, which is essential for translating lab-scale assays into field-ready sensors.

The success of CQDs in these matrices stems from their high photostability and adaptability to surface formats, yet further work is needed to minimize color interference and scattering from natural pigments, possibly through ratiometric or dual-emission designs that internally correct for optical distortion. Although lab-scale CQD synthesis demonstrates high reproducibility, translating these sensors to field-scale deployment remains challenging due to batch-to-batch variability and storage stability. Continuous-flow or microwave-assisted syntheses, combined with standardized functionalization protocols, can improve reproducibility and enable scalable production of robust CQD sensors.

6.4. Urine (biomonitoring) and the central role of PNP (p-nitrophenol)

Among OP metabolites, p-nitrophenol is both analytically convenient and toxicologically relevant and is listed by the U.S. p-Nitrophenol is listed by the U.S. EPA as a screening compound in the draft prioritized substances list.¹³¹ EPA is one of the priority pollutants, and this has stimulated standardized analytical procedures and on-going monitoring. CQD probes now cover from laboratory sensitivity to point of care convenience for PNP in urine, an important matrix for occupational/environmental exposure analysis. Recently, by taking advantage of the “self-exothermic-reaction assisted” green CD synthesis, a fluorescence assay was reported to sensitively and accurately quantify p-NP in water and in human urine with matrix-tolerant recovery and low-nM sensitivity without elaborate sample cleanup.¹³² For those analytes that require regulatory verification, CQD-positive screens can be reflexed to validated EPA/ATSDR methods (e.g. SPE-GC/MS) for quantitation and legal defensibility, but cost and turnaround time are drastically reduced by the initial CQD pass. Urine, being an intricate biological fluid, also exhibits intense auto fluorescence, protein binding, and ionic interference that have the potential to skew CQD signals. The stability of doped or passivated CQDs, combined with the optimized dilution and filtration steps, readily suppresses most of these interferences and allows for effective recovery and quantitation of PNP at trace concentrations. Urine presents strong autofluorescence, protein binding, and ionic interference. PET-based quenching by p-nitrophenol may be affected by competing interactions with proteins or salts. Passivated or heteroatom-doped CQDs demonstrate enhanced stability and selectivity, but rigorous validation across diverse patient samples is required to ensure accurate quantification for occupational and environmental monitoring. Standardized calibration and internal controls are recommended for reliable measurements in such complex biological matrices. Additional extensive validation on variable pH, storage parameters, and patient groups needs to be conducted for complete clinical application.

6.5. Laboratory proof-of-concept vs. real-world validation

While many CQD-based sensors for the detection of organophosphate (OP) compounds have been described, most are still in the laboratory proof-of-concept stage. They are normally tested in buffered or deionised water, where environmental interference is minimal. Under such idealised circumstances, the LODs have been as low as 0.2–2 nM for parathion, chlorpyrifos, and malathion, with linear ranges up to 10–50 μM and RSDs less than 3–5%, proving outstanding precision.^45–50 Nevertheless, such values tend to overestimate sensor performance in real samples since these do not have ionic strength variation, organic matter, and competing analytes.

Conversely, true-matrix validations with natural water, soil solutions, fruit juices, or human urine make up a smaller but increasing body of research. In such experiments, CQD sensors typically exhibit LODs between 5–50 nM, recovery efficiencies of 85–100%, and RSDs ranging from 5–12%, indicating some signal damping but analytically acceptable reproducibility.^44–47 For instance, nitrogen-doped CQDs identified parathion in river water (LOD = 6.8 nM, recovery = 94%), sulfur-doped CQDs measured malathion in soil eluates (LOD = 11 nM, recovery = 90–96%), and green-synthesised CQDs realised PNP quantification in human urine (LOD ≈ 8 nM, recovery = 92%) without extensive pre-treatment.^133,134

The contrast highlights that whereas lab-based experiments demonstrate maximal sensitivity, realistic performance parameters necessary for field translation are provided by matrix-validated assays. To bring them closer, upcoming research must implement matrix-spiking validation protocols, inter-laboratory reproducibility evaluations, and standard performance parameters (LOD, recovery, RSD). Quantitative harmonisation in this manner will speed the transformation of CQD sensors from bench-top prototyping to stable, field-deployable monitoring devices for pesticides and their toxic metabolites. Laboratory LODs often overestimate sensor performance due to minimal interference. Real-world validations provide more realistic performance metrics but highlight challenges in reproducibility and stability. Inter-laboratory standardization, matrix-spiking protocols, and long-term storage studies are essential to establish reliable and regulatory-compliant CQD assays. Future improvements could include multiplexed detection, integration with portable devices, and hybrid optical–electrochemical sensors to extend sensitivity while maintaining robustness in complex matrices.

7. Analytical performance and mechanisms

Using matrices, CQD sensors for OPs and PNP have routinely offered LOD values from single-nM to a few tens of nM, wide linear ranges spanning at least one to two orders of magnitude, and rapid responses, often in the s to min time scale.¹³⁵ Mechanistically, PET dominates if the OP or PNP is an electron acceptor (e.g., nitro-aromatics) whereas IFE dominates if there is absorption by the analyte in the CQD excitation/emission bands (ubiquitous for PNP at ∼400 nm under alkaline conditions).¹³⁶

Importantly, the efficiency of PET, IFE, or FRET pathways is directly modulated by CQD structural features, including heteroatom doping and defect density. Nitrogen-doped CQDs enhance electron-donor capability for PET quenching with nitroaromatic OPs, whereas sulfur doping tunes the bandgap to favor selective FRET interactions. Surface defects introduce localized trap states, which may enhance or suppress quenching depending on analyte binding and the matrix environment.

In radiometric schemes, where donor–acceptor pairs are in the 1–10 nm range, FRET routes become important and improve immunity to intensity drift and turbidity. CQD/GQD based electrochemical transduction is an alternative modality of detection and provides increased sensitivity through catalytic surface states and defect-assisted charge transfer, in addition to purely optical detection modalities.¹³⁷ The heteroatom co-doping (N, S) and biomass-based feeds are especially highlighted in the literature of 2023–2025, as these approaches provide a route to high-QY, defect-engineered dots that maintain brightness and selective quencher interaction.^138,139 Thus, CQDs offer the dual detection routes, optical and electrochemical, in order to provide versatile detection in complex matrices.

7.1. Validation, practical deployment, and regulatory considerations

Field applicability is a function of three pillars: raw accuracy against an ideal gold standard, matrix tolerance, and operational convenience. Optical CQD readouts and voltammetric GQD sensors have both been calibrated with HPLC/GC-MS for very close agreement in spiked and environmental samples for malathion in water and food rinsates affirming their application as primary screens.¹⁴⁰ A number of Cu-doped, green-synthesized PNP CD families have been designed as inhibitors of interfering agents (ascorbates, phenolics) while maintaining the traditional alkaline absorption/emission interaction that enables colorimetric/fluorometric selectivity.¹⁴¹ Importantly, multiple open-access publications report recoveries generally >90–103% in spiked natural water and produce washes and specific detection in human urine, so CQDs may be used as valid tools for exposure studies in agricultural workers exposed or residents living near treated fields.¹⁴²

Despite these successes, matrix variability remains a critical challenge. Humic substances, dissolved organics, and co-existing metal ions in water or soil can partially suppress fluorescence quenching, whereas pigments and sugars in produce and auto-fluorescence/protein binding in urine may distort signals. Standardization of CQD synthesis, doping, and surface functionalization is therefore necessary to achieve reproducible LODs and reliable field performance across diverse matrices. Ratiometric or dual-emission designs, exploiting defect-engineered or doped sites, offer potential solutions for self-correcting intensity fluctuations in complex samples.

7.2. Practical deployment and regulatory context

Since PNP is an EPA priority pollutant and OP residues in food/water are regulated by FAO/WHO and national guidelines, calibration of CQD sensors needs to be established at decision levels appropriate for each matrix.¹⁴³ Two operational schemes are helpful: (i) two point bracketing around the action limit (e.g. spiking 0.5× and 2×), and (ii) ratiometric designs which can self-correct for intensity fluctuations.¹⁴⁴ Where confirmatory analysis is required (compliance investigations, forensic) the CQD result is used as an economical triage step to define which samples will go on to EPA Method 528 (phenols by SPE-GC/MS) or pesticide focussed LC-MS/MS panels.¹⁴⁵ For aqueous, a handheld fluorimeter or smartphone-compatible lateral-flow-type strip functionalized with CQDs can be used for near-real-time triage at well heads and irrigation canals; positive/indeterminate results may be stabilized by on-strip derivatization and then sent for confirmation. For soil, trade-offs between sensitivity and logistics are made between gentle extraction and either cuvette fluorescence or disposable-electrode voltammetry; doped CQDs help circumvent chromophoric humics and allow for quantitative measurements. For produce, swab-and-read paper samplers with matrix-matched calibration on rinse waters from produce;¹⁴⁶ for urine, environmental PNP chemistry for CQD with minimal pH and ionic strength changes; cut-offs may be set based on expected exposures for occupational sampling using external standards checked by internal GC/MS as needed. These developments are in line with a broader trend seen in recent reviews: CQDs are moving from bench-top proof-of-concept to integrated, portable, point-and-shoot diagnostic systems for food safety and exposure science.¹⁴⁷ The best OP/PNP assays are the ones that combine green synthesis (biomass-based precursors, non-toxic solvents) with defect and surface-state engineering, in order to combine high quantum yield, selective interaction of the analyte and suppression of false positives.¹⁴⁸ Hybridization of electrochemical signals with optical CQDs/GQDs is a promising strategy for extending the LODs further into the sub-nM region, without sacrificing portability. Finally, due to the fact that PNP is also a regulatory target, further efforts on urine-compatible CQD assays against reference EPA/ATSDR methods will further bridge the gap between environmental monitoring and human health risk assessment.

Hybrid optical–electrochemical systems are increasingly recognized as a strategy to extend LODs into the sub-nM range while retaining portability and operational simplicity. Coupled with green synthesis (biomass-based precursors, non-toxic solvents), defect and surface-state engineering, CQDs can achieve high quantum yield, selective analyte interaction, and suppression of false positives. Field-ready assays must incorporate matrix validation, inter-laboratory reproducibility checks, and calibration protocols tailored to regulatory thresholds to bridge the gap between laboratory performance and real-world application. Continuous-flow or microwave-assisted synthesis protocols combined with standardized functionalization can further enhance reproducibility and scalability, enabling CQDs to transition from bench-top proof-of-concept to robust environmental and occupational monitoring tools.

8. Future prospects and challenges

Carbon quantum dots have emerged as highly promising, sensitive and versatile sensors for pesticide detection in a wide variety of matrices. However, to get from proof-of-concept demonstrations to tools used in the real world, further progress is needed. Green and scalable synthesis will continue to be at the core, both to guarantee low-cost deployment, and to be in line with sustainability targets of agricultural monitoring. The next generation of CQDs will be constructed from non-toxic biomass precursors, low-toxicity solvents, and defect/surface engineering strategies that will simultaneously improve quantum yield and selectivity while minimizing the environmental footprint of nanomaterial manufacturing. Similarly, portable formats–such as paper-based sensors, smartphone-integrated readouts and microfluidic devices–are likely to further extend access to rapid on-site pesticide analysis. Importantly, the integration of environmental monitoring with biomonitoring of human exposure (i.e., urine-based CQD assays for p-nitrophenol) might open a novel translational pathway, which can directly link pesticide use patterns and health risk assessment.

Despite this conceptual promise, several challenges must be addressed before CQDs can become mainstream analytical platforms. The complexity of real-world samples ranging from colored fruit extracts and humic-rich soils to urine containing endogenous interferents continues to affect reproducibility, signal stability, and quantitative accuracy. Such interference often leads to fluorescence quenching or false-positive responses, requiring rigorous matrix calibration and hybrid optical–electrochemical strategies to mitigate artifacts. Batch-to-batch variability in quantum yield, arising from subtle changes in precursor composition, dopant concentration, or synthesis temperature, remains a major limitation that hampers standardization and large-scale production. In addition, green-synthesized CQDs frequently exhibit storage instability and surface oxidation over time, which can degrade fluorescence response and reduce operational shelf life. From a translational standpoint, CQD-based sensors still require validation against gold-standard analytical methods such as GC-MS and LC-MS/MS to gain regulatory acceptance. For the near term, their practical role may therefore lie in rapid preliminary screening rather than definitive quantification. Broader adoption will depend on standardized synthesis protocols, inter-laboratory reproducibility studies, and inclusion in formal environmental monitoring guidelines. Finally, integration with digital platforms like IoT-enabled field kits, wireless data sharing, and cloud-based pesticide mapping could significantly expand their utility within precision agriculture and environmental health surveillance.

Taken together, CQDs will likely move from bench-scale innovation to field-ready, regulation-compliant diagnostic systems in the next few years. The twin challenge of matrix tolerance and regulatory acceptance, along with advances in sustainable synthesis, and portable form will determine whether CQDs evolve into the new benchmark in analytical methods for pesticide detection and exposure science.

9. Conclusion

Pesticide contamination continues to be one of the serious environmental and public health issues, particularly in intensive agriculture belts like India. While traditional chromatographic and spectrometric techniques provide high precision, they are expensive, time-consuming, and not suited for on-site measurements. Carbon quantum dots (CQDs) are increasingly becoming alternatives due to low-cost synthesis, chemical tunability, and outstanding optical properties. Recent research shows their potential to detect organophosphates (OPs) and their toxic metabolite p-nitrophenol (PNP) in varied samples with great sensitivity and reproducibility. Future research should aim to create field-deployable, portable sensing devices, such as paper-based devices and smartphone-based systems, for fast on-site analysis. Standardisation of the choice of biomass precursors and synthesis protocols is critical to enhance reproducibility and compare between studies. In addition, systematic analysis of long-term stability and storage performance will provide assurance for sensor reliability under realistic conditions. Combining CQDs with hybrid nanomaterials (e.g., MOFs, metal oxides, and MIPs) may further allow for the enhancement of selectivity and robustness in complicated matrices. Standard performance metrics and validation frameworks will be essential for real-world applications and regulatory approval. In general, CQDs exhibit enormous potential as portable, low-cost, and sustainable sensing materials for monitoring exposures and detecting pesticides.

Author contributions

N. S. and V. P. drafted the manuscript. N. S. and V. P. formatted the manuscript. T. P. finalized the manuscript with proper review. N. S. formatted the figures.

Conflicts of interest

This work has no conflict of interest.

Abbreviations

OPs	Organophosphate pesticides
PET	Photoinduced electron transfer
CQDS	Carbon quantum dots
IFE	Inner filter effect
OP	Organophosphate
FRET	Förster resonance energy transfer
PNP	p-Nitrophenol
AChE	Acetylcholinesterase
LOD	Limit of detection

Data availability

No primary research results, software or code have been included and no new data were generated or analysed as part of this review.

Acknowledgements

Authors acknowledge Lovely Professional University for providing the opportunity to work. There is no funding for this manuscript.

References

1. K. Oginawati, S. H. Susetyo, S. I. Rahmawati, S. B. Kurniawan and S. R. S. Abdullah, Distribution of organochlorine pesticide pollution in water, sediment, mollusk, and fish at Saguling Dam, West Java, Indonesia, Toxicol. Res., 2022, 38(2), 149–157.
2. F. Kamel and J. A. Hoppin, Association of pesticide exposure with neurologic dysfunction and disease, Environ. Health Perspect., 2004, 112(9), 950–958.
3. R. Jayaraj, P. Megha and P. Sreedev, Organochlorine pesticides, their toxic effects on living organisms and their fate in the environment, Interdiscip. Toxicol., 2016, 9(3–4), 90.
4. S. Gangemi, E. Miozzi, M. Teodoro, G. Briguglio, A. De Luca, C. Alibrando and M. Libra, Occupational exposure to pesticides as a possible risk factor for the development of chronic diseases in humans, Mol. Med. Rep., 2016, 14(5), 4475–4488.
5. J. da Silva Sousa, H. O. do Nascimento, H. de Oliveira Gomes and R. F. do Nascimento, Pesticide residues in groundwater and surface water: Recent advances in solid-phase extraction and solid-phase microextraction sample preparation methods for multiclass analysis by gas chromatography-mass spectrometry, Microchem. J., 2021, 168, 106359.
6. E. L. Robb, A. C. Regina and M. B. Baker, Organophosphate toxicity, 2017.
7. A. Massoud, M. SaadAllah, N. A. Dahran, N. E. Nasr, I. El-Fkharany, M. S. Ahmed and A. Derbalah, Toxicological effects of Malathion at low dose on Wister male rats with respect to Biochemical and Histopathological alterations, Front. Environ. Sci., 2022, 10, 860359.
8. C. Mittal, S. Singh, P. Kumar-M and S. B. Varthya, Toxicoepidemiology of poisoning exhibited in Indian population from 2010 to 2020: a systematic review and meta-analysis, BMJ Open, 2021, 11(5), e045182.
9. A. Almási, P. Perjési and E. Fischer, The relative importance of the small intestine and the liver in Phase II metabolic transformations and elimination of p-nitrophenol administered in different doses in the rat, Sci. Pharm., 2020, 88(4), 51.
10. S. Salem, R. El-Shaheny and N. A. Abdallah, Transforming a traditional ethnic beverage into highly emissive CDs as a sensitive nanosensor for the anti-malignant hyperthermia drug dantrolene sodium in pharmaceuticals and plasma. An economic and sustainable approach, Talanta Open, 2025, 100549.
11. E. A. Ahmed, H. E. Khaled and A. K. Elsayed, Long-term exposure to p-Nitrophenol induces hepatotoxicity via accelerating apoptosis and glycogen accumulation in male Japanese quails, Environ. Sci. Pollut. Res., 2021, 28(32), 44420–44431.
12. H. Xia, W. Zhang, Z. Yang, Z. Dai and Y. Yang, Spectrophotometric Determination of p-Nitrophenol under ENP Interference, J. Anal. Methods Chem., 2021, 2021(1), 6682722.
13. C. A. Valdez and R. N. Leif, Analysis of organophosphorus-based nerve agent degradation products by gas chromatography-mass spectrometry (GC-MS): Current derivatization reactions in the analytical chemist's toolbox, Molecules, 2021, 26(15), 4631.
14. T. Liu, J. X. Dong, S. G. Liu, N. Li, S. M. Lin, Y. Z. Fan and N. B. Li, Carbon quantum dots prepared with polyethyleneimine as both reducing agent and stabilizer for synthesis of Ag/CQDs composite for Hg2+ ions detection, J. Hazard. Mater., 2017, 322, 430–436.
15. S. Ostovar, M. Pourmadadi, A. Shamsabadipour and P. Mashayekh, Nanocomposite of chitosan/gelatin/carbon quantum dots as a biocompatible and efficient nanocarrier for improving the Curcumin delivery restrictions to treat brain cancer, Int. J. Biol. Macromol., 2023, 242, 124986.
16. A. R. Gopal, F. Joy, V. Dutta, J. Devasia, R. Dateer and A. Nizam, Carbon dot-based fluorescence resonance energy transfer (FRET) systems for biomedical, sensing, and imaging applications, Part. Part. Syst. Charact., 2024, 41(1), 2300072.
17. T. Vyas, S. Jaiswal, S. Choudhary, P. Kodgire and A. Joshi, Recombinant Organophosphorus acid anhydrolase (OPAA) enzyme-carbon quantum dot (CQDs)-immobilized thin film biosensors for the specific detection of Ethyl Paraoxon and Methyl Parathion in water resources, Environ. Res., 2024, 243, 117855.
18. S. Shaktawat, S. K. Yadav, D. Singh and J. Singh, Green Synthesis of Carbon Quantum Dots Through Various Strategies, in Green Carbon Quantum Dots: Environmental Applications, Springer Nature Singapore, Singapore, 2024, pp. 25–53.
19. V. Pandey, A. Chauhan, G. Pandey and M. K. R. Mudiam, Optical sensing of 3-phenoxybenzoic acid as a pyrethroid pesticides exposure marker by surface imprinting polymer capped on manganese-doped zinc sulfide quantum dots, Anal. Chem. Res., 2015, 5, 21–27.
20. I. Eliboev, A. Ishankulov, E. Berdimurodov, K. Chulpanov, M. Nazarov, B. Jamshid, B. Toshpulotov, R. Tukhtaeva, M. Demir, K. Rashidova, F. Jalilov and K. Polvonov, Advancing analytical chemistry with carbon quantum dots: a comprehensive review, Anal. Methods, 2025, 17(13), 2627–2649.
21. H. Xia, W. Zhang, Z. Yang, Z. Dai and Y. Yang, Spectrophotometric Determination of p-Nitrophenol under ENP Interference, J. Anal. Methods Chem., 2021, 2021(1), 6682722.
22. N. Pajooheshpour, M. Rezaei, A. Hajian, A. Afkhami, M. Sillanpää, F. Arduini and H. Bagheri, Protein templated Au-Pt nanoclusters-graphene nanoribbons as a high performance sensing layer for the electrochemical determination of diazinon, Sens. Actuators, B, 2018, 275, 180–189.
23. A. Karunarathne, D. Gunnell, F. Konradsen and M. Eddleston, How many premature deaths from pesticide suicide have occurred since the agricultural Green Revolution?, Clin. Toxicol., 2020, 58(4), 227–232.
24. P. Varghese and T. B. Erickson, Pesticide poisoning among children in India: The need for an urgent solution, Glob. Pediatr. Health, 2022, 9, 2333794X221086577.
25. S. Sarkar, Despite historic bans, south Asia still struggles with pesticide suicides, BMJ, 2023, 381 DOI:10.1136/bmj.p678.
26. C. Wang, Y. Zhang, W. Diao and H. Wang, Extracting rooftops from remote sensing images using both top-down and bottom-up processes, Remote Sens. Lett., 2017, 8(6), 586–595.
27. M. Aksu and Ö. Güzdemir, Food Waste-Derived Carbon Quantum Dots and Their Applications in Food Technology: A Critical Review, Food Bioprocess Technol., 2025, 1–26.
28. M. Roostaee and R. Ranjbar-Karimi, Emerging trends in carbon quantum dots: Synthesis, characterization, and environmental photodegradation applications, Mater. Sci. Semicond. Process., 2025, 188, 109212.
29. F. Chen, T. H. Yan, S. Bashir and J. L. Liu, Synthesis of nanomaterials using top-down methods, in Advanced nanomaterials and their applications in renewable energy, 2022, pp. 37–60.
30. A. B. Cook and T. D. Clemons, Bottom-up versus top-down strategies for morphology control in polymer-based biomedical materials, Adv. NanoBiomed Res., 2022, 2(1), 2100087.
31. S. Palagati and J. Reddy, Synthesis by top-down and Bottom-Up, in Adv. Mater.: Prod. Char. Multidiscip. App., 2024, vol. 201.
32. S. Tripathy, J. Rodrigues and N. G. Shimpi, Top-down and Bottom-up Approaches for Synthesis of Nanoparticles, in Nanobiomaterials Perspect, Med. Appl. Diagn. Treat. Dis, 2023, vol. 145, pp. 92–130.
33. A. K. Vijay and G. S. Rolly, Diverse Carbon Nanomaterials for Environment: Synthesis Route and Properties, in Carbon: Bulk-to-Nano Forms for Detection and Remediation of Environmental Contaminants, Springer Nature Switzerland, Cham, 2025, pp. 27–55.
34. M. Usman and S. Cheng, Recent trends and advancements in green synthesis of biomass-derived carbon dots, Eng, 2024, 5(3), 2223–2263.
35. N. Abid, A. M. Khan, S. Shujait, K. Chaudhary, M. Ikram, M. Imran, J. Haider, M. Khan, Q. Khan and M. Maqbool, Synthesis of nanomaterials using various top-down and bottom-up approaches, influencing factors, advantages, and disadvantages: A review, Adv. Colloid Interface Sci., 2022, 300, 102597.
36. L. Zhu, D. Shen, C. Wu and S. Gu, State-of-the-art on the preparation, modification, and application of biomass-derived carbon quantum dots, Ind. Eng. Chem. Res., 2020, 59(51), 22017–22039.
37. M. M. Osman, R. El-Shaheny and F. A. Ibrahim, Alfalfa biomass as a green source for the synthesis of N, S-CDs via microwave treatment. Application as a nano sensor for nifuroxazide in formulations and gastric juice, Anal. Chim. Acta, 2024, 1319, 342946.
38. R. Hesham, H. Abd El-Aziz and R. El-Shaheny, Utility of cauliflower waste/garlic biomass admixture for green synthesis of multi-doped CQDs as a fluorescent optosensor for Fe3+ in different matrices, Microchem. J., 2025, 208, 112322.
39. V. Arul, R. Suresh, P. Chandrasekaran and K. Radhakrishnan, Optical and Biomedical Features of Green Carbon Quantum Dots, in Green Carbon Quantum Dots: Environmental Applications, Springer Nature Singapore, Singapore, 2024, pp. 85–116.
40. Y. Ren, Z. Ma, T. Gao and Y. Liang, Advance progress on luminescent sensing of nitroaromatics by crystalline lanthanide–organic complexes, Molecules, 2023, 28(11), 4481.
41. N. A. Qandeel, A. A. El-Masry, M. Eid, M. A. Moustafa and R. El-Shaheny, Fast one-pot microwave-assisted green synthesis of highly fluorescent plant-inspired S, N-self-doped carbon quantum dots as a sensitive probe for the antiviral drug nitazoxanide and hemoglobin, Anal. Chim. Acta, 2023, 1237, 340592.
42. T. Biswas, J. Raut, D. De and P. Sahoo, Nanosensors for hazardous pesticides and nanofertilizers for sustainable agriculture: contribution of carbon quantum dots, Dalton Trans., 2025, 54(25), 9835–9849.
43. R. Pratap, S. Pandey, V. Vishal, I. Raghuvanshi, S. Kumar, J. Lahiri and A. S. Parmar, Sensing of p-nitrophenol using highly selective and sensitive Boran, Nitrogen doped quantum dots, Chem. Phys. Impact, 2024, 9, 100697.
44. A. Kundu, B. Maity and S. Basu, Orange pomace-derived fluorescent carbon quantum dots: detection of dual analytes in the nanomolar range, ACS Omega, 2023, 8(24), 22178–22189.
45. Y. Chen, Y. Zhou, J. You, Z. Zhang, A. Sun, H. Liu and X. Shi, Fluorescent Molecular Imprinted Sensor Based on Carbon Quantum Dot for Nitrofen Detection in Water Sample, Polymer, 2025, 17(6), 816.
46. N. Mahmoudi, F. Fatemi, M. Rahmandoust, F. Mirzajani and S. O. R. Siadat, Development of a carbon quantum dot-based sensor for the detection of acetylcholinesterase and the organophosphate pesticide, Heliyon, 2023, 9(9), e19551.
47. X. Wu, Y. Song, X. Yan, C. Zhu, Y. Ma, D. Du and Y. Lin, Carbon quantum dots as fluorescence resonance energy transfer sensors for organophosphate pesticides determination, Biosens. Bioelectron., 2017, 94, 292–297.
48. J. Wang, T. Lu, Y. Hu, X. Wang and Y. Wu, A label-free and carbon dots based fluorescent aptasensor for the detection of kanamycin in milk, Spectrochim. Acta, Part A, 2020, 226, 117651.
49. J. Niu and H. Gao, Synthesis and drug detection performance of nitrogen-doped carbon dots, J. Lumin., 2014, 149, 159–162.
50. Y. Zhu, Y. Lu, L. Shi and Y. Yang, β-Cyclodextrin functionalized N, Zn codoped carbon dots for specific fluorescence detection of fluoroquinolones in milk samples, Microchem. J., 2020, 153, 104517.
51. J. Tang, J. Zhang, Y. Zhang, Y. Xiao, Y. Shi, Y. Chen and W. Xu, Influence of group modification at the edges of carbon quantum dots on fluorescent emission, Nanoscale Res. Lett., 2019, 14(1), 241.
52. X. Yao, R. E. Lewis and C. L. Haynes, Synthesis processes, photoluminescence mechanism, and the toxicity of amorphous or polymeric carbon dots, Acc. Chem. Res., 2022, 55(23), 3312–3321.
53. H. Shabbir, E. Csapó and M. Wojnicki, Carbon quantum dots: the role of surface functional groups and proposed mechanisms for metal ion sensing, Inorganics, 2023, 11(6), 262.
54. M. A. El Hamd, M. El-Maghrabey, S. Almawash, A. S. Radwan, R. El-Shaheny and G. Magdy, Citrus/urea nitrogen-doped carbon quantum dots as nanosensors for vanillin determination in infant formula and food products via factorial experimental design fluorimetry and smartphone, Luminescence, 2024, 39(2), e4643.
55. M. L. Liu, L. Yang, R. S. Li, B. B. Chen, H. Liu and C. Z. Huang, Large-scale simultaneous synthesis of highly photoluminescent green amorphous carbon nanodots and yellow crystalline graphene quantum dots at room temperature, Green Chem., 2017, 19(15), 3611–3617.
56. M. Kovačova, E. Špitalská, Z. Markovic and Z. Špitálský, Carbon quantum dots as antibacterial photosensitizers and their polymer nanocomposite applications, Part. Part. Syst. Charact., 2020, 37(1), 1900348.
57. M. Chaudhary, P. Singh, G. P. Singh and B. Rathi, Structural features of carbon dots and their agricultural potential, ACS Omega, 2024, 9(4), 4166–4185.
58. N. A. Qandeel and R. El-Shaheny, Unlocking multifaceted applications of fava bean empty pods-derived CQDs for smart multi-target nanoprobing of pH, temperature, and p-nitrophenol, Microchem. J., 2025, 209, 112869.
59. G. Speranza, Characterization of Carbon Nanostructures by Photoelectron Spectroscopies, Materials, 2022, 15(13), 4434.
60. S. Ganguly, P. Das, S. Banerjee and N. C. Das, Advancement in science and technology of carbon dot-polymer hybrid composites: a review, Funct. Compos. Struct., 2019, 1(2), 022001.
61. L. H. Madkour, Carbon-Based Nanocomposite Applications and Microelectronic Technologies, CRC Press, 2024.
62. W. You, W. Zou, S. Jiang, J. Zhang, Y. Ge, G. Lu and J. H. Pan, Fluorescent carbon quantum dots with controllable physicochemical properties fantastic for emerging applications: A review, Carbon Neutralization, 2024, 3(2), 245–284.
63. H. Sun and P. Wu, Tuning the functional groups of carbon quantum dots in thin film nanocomposite membranes for nanofiltration, J. Membr. Sci., 2018, 564, 394–403.
64. C. M. Luk, Fabrication and Characterization of Graphene quantum dots for electronic and optoelectronic applications, PhD, Hong Kong Polytechnic University, 2015.
65. A. R. Sadrolhosseini, S. A. Rashid, N. Jamaludin and A. M. Isloor, Experimental and molecular modeling of interaction of carbon quantum dots with glucose, Appl. Phys. A: Mater. Sci. Process., 2019, 125(8), 529.
66. R. Yadav, A. Yadav and V. Lahariya, The Study of Tunable Excitation Independent and Dependent Photoluminescence Behaviour of P-Functionalized Carbon Dots, J. Nano Res., 2024, 86, 67–76.
67. G. C. D. Fonseca, Boosting light-driven photoelectrocatalytic water oxidation by using green source-based carbon quantum dots, Masters, Goiano Federal Institute, 2024.
68. H. Li, Y. Zhang, J. Huang, Z. Zhang, X. Li, J. Su and W. Cai, Polygonatum cyrtonema Hua residue carbon quantum dots as fluorescent probes for detecting organophosphorus pesticide residues, Ind. Crops Prod., 2025, 235, 121761.
69. M. Kaur, M. Bhattacharya and B. Maity, Deep eutectic solvent-assisted carbon quantum dots for nanomolar detection of 4-nitrophenol, RSC Adv., 2025, 15(25), 19884–19898.
70. L. Li and T. Dong, Photoluminescence tuning in carbon dots: surface passivation or/and functionalization, heteroatom doping, J. Mater. Chem. C, 2018, 6(30), 7944–7970.
71. C. Wang, C. Wei, H. Niu, L. Xu and X. Liu, Graded nitro-engineering strategy: Tuning surface states and sp² conjugated domains of carbon quantum dots for full-color emission, Chin. Chem. Lett., 2025, 111296.
72. M. C. Drummer, V. Singh, N. Gupta, J. L. Gesiorski, R. B. Weerasooriya and K. D. Glusac, Photophysics of nanographenes: from polycyclic aromatic hydrocarbons to graphene nanoribbons, Photosynth. Res., 2022, 151(2), 163–184.
73. J. Zhang, S. Chu, C. Tao, J. Yan, Y. Jiang and Y. Lu, Nitrogen-doped carbon dots as efficient turn-on fluorescent probe for assay of organophosphorus pesticides, ChemPhysMater, 2024, 3(4), 462–469.
74. R. El-Shaheny, L. Al-Khateeb, M. El-Maghrabey, G. Magdy and H. M. Hashem, Double-reverse-signal ratiometric fluorescence probe for residual determination of Chlorpyrifos pesticide in surface water based on scalable upcycling of rice straw to luminescent CQDs via energy-efficient alkali treatment, Talanta Open, 2025, 11, 100427.
75. S. Wahyudi, I. Rizoputra, C. Panatarani and A. Bahtiar, Development of novel aptasensor based carbon nano dots (CNDs) with FRET mechanism for detection of organophosphorus pesticides, Appl. Food Res., 2025, 101172.
76. X. Dou, K. Sun, H. Chen, Y. Jiang, L. Wu, J. Mei and J. Xie, Nanoscale metal-organic frameworks as fluorescence sensors for food safety, Antibiotics, 2021, 10(4), 358.
77. R. Zhang, L. Zhang, R. Yu and C. Wang, Rapid and sensitive detection of methyl parathion in rice based on carbon quantum dots nano-fluorescence probe and inner filter effect, Food Chem., 2023, 413, 135679.
78. D. H. Nguyen, A. Muthu, T. Elsakhawy, M. H. Sheta, N. Abdalla, H. El-Ramady and J. Prokisch, Carbon Nanodots-Based Sensors: A Promising Tool for Detecting and Monitoring Toxic Compounds, Nanomaterials, 2025, 15(10), 725.
79. J. Mondal, R. Lamba, Y. Yukta, R. Yadav, R. Kumar, B. Pani and B. Singh, Advancements in semiconductor quantum dots: expanding frontiers in optoelectronics, analytical sensing, biomedicine, and catalysis, J. Mater. Chem. C, 2024, 12(28), 10330–10389.
80. K. F. Kayani, M. K. Rahim, S. J. Mohammed, H. R. Ahmed, M. S. Mustafa and S. B. Aziz, Recent progress in folic acid detection based on fluorescent carbon dots as sensors: a review, J. Fluoresc., 2025, 35(5), 2481–2494.
81. X. Huang, C. Yang, Y. Chen, Z. Zhu and L. Zhou, Cuttlefish ink-based N and S co-doped carbon quantum dots as a fluorescent sensor for highly sensitive and selective para-nitrophenol detection, Anal. Methods, 2021, 13(44), 5351–5359.
82. S. Tao, S. Zhu, T. Feng, C. Xia, Y. Song and B. Yang, The polymeric characteristics and photoluminescence mechanism in polymer carbon dots: A review, Mater. Today Chem., 2017, 6, 13–25.
83. G. Somaraj, S. Mathew, T. Abraham, K. G. Ambady, C. Mohan and B. Mathew, Nitrogen and Sulfur Co-Doped Carbon Quantum Dots for Sensing Applications: A Review, ChemistrySelect, 2022, 7(19), e202200473.
84. M. J. Molaei, Principles, mechanisms, and application of carbon quantum dots in sensors: a review, Anal. Methods, 2020, 12(10), 1266–1287.
85. D. Udhayakumari, D. Duraisamy and A. Nanthakumar, PET coordination mechanism for the detecting of environmental toxic analytes: current approaches and future directions, J. Fluoresc., 2025, 1–17.
86. A. Xu, G. Wang, Y. Li, H. Dong, S. Yang, P. He and G. Ding, Carbon-based quantum dots with solid-state photoluminescent: mechanism, implementation, and application, Small, 2020, 16(48), 2004621.
87. C. M. Marian, Understanding and controlling intersystem crossing in molecules, Annu. Rev. Phys. Chem., 2021, 72(1), 617–640.
88. S. Paul, P. Daga and N. Dey, Exploring various photochemical processes in optical sensing of pesticides by luminescent nanomaterials: A concise discussion on challenges and recent advancements, ACS Omega, 2023, 8(47), 44395–44423.
89. Y. Jia and X. Yao, Defects in carbon-based materials for electrocatalysis: synthesis, recognition, and advances, Acc. Chem. Res., 2023, 56(8), 948–958.
90. J. Zhu and S. Mu, Defect engineering in carbon-based electrocatalysts: insight into intrinsic carbon defects, Adv. Funct. Mater., 2020, 30(25), 2001097.
91. R. Nandee, M. A. Chowdhury, N. Hossain, M. M. Rana, M. H. Mobarak, M. A. Islam and H. Aoyon, Experimental characterization of defect-induced Raman spectroscopy in graphene with BN, ZnO, Al2O3, and TiO2 dopants, Results Eng., 2024, 21, 101738.
92. P. Feicht and S. Eigler, Defects in graphene oxide as structural motifs, ChemNanoMat, 2018, 4(3), 244–252.
93. X. Yan, L. Zhuang, Z. Zhu and X. Yao, Defect engineering and characterization of active sites for efficient electrocatalysis, Nanoscale, 2021, 13(6), 3327–3345.
94. J. Wang, X. Duan, J. Gao, Y. Shen, X. Feng, Z. Yu and S. Wang, Roles of structure defect, oxygen groups and heteroatom doping on carbon in nonradical oxidation of water contaminants, Water Res., 2020, 185, 116244.
95. Y. Han, Y. Tian, Q. Li, T. Yao, J. Yao, Z. Zhang and L. Wu, Advances in detection technologies for pesticide residues and heavy metals in rice: A comprehensive review of spectroscopy, chromatography, and biosensors, Foods, 2025, 14(6), 1070.
96. M. Cacioppo, Synthesis of Nitrogen Doped Carbon Nanodots and their Applications as Functional Materials, PhD, University of Trieste, 2020.
97. S. Srinivasan, D. Raajasubramanian, N. Ashokkumar, V. Vinothkumar, N. Paramaguru, P. Selvaraj and R. Murali, Nanobiosensors based on on-site detection approaches for rapid pesticide sensing in the agricultural arena: A systematic review of the current status and perspectives, Biotechnol. Bioeng., 2024, 121(9), 2585–2603.
98. V. B. Silva, Y. H. Santos, R. Hellinger, S. Mansour, A. Delaune, J. Legros and E. S. Orth, Organophosphorus chemical security from a peaceful perspective: sustainable practices in its synthesis, decontamination and detection, Green Chem., 2022, 24(2), 585–613.
99. Y. Wang, Y. Ma, C. Zhang, Y. Shen, D. Zhang, S. Huang and P. Li, Exclusion of the main role of oxygen vacancy in Cu-Mn-O/N-doped carbon catalysts for activating peroxymonosulfate to degrade p-nitrophenol (PNP) and reducing PNP in water by NaBH4, J. Environ. Chem. Eng., 2024, 12(4), 113100.
100. D. M. Jameson and J. A. Ross, Fluorescence polarization/anisotropy in diagnostics and imaging, Chem. Rev., 2010, 110(5), 2685–2708.
101. D. Genovese, M. Cingolani, E. Rampazzo, L. Prodi and N. Zaccheroni, Static quenching upon adduct formation: a treatment without shortcuts and approximations, Chem. Soc. Rev., 2021, 50(15), 8414–8427.
102. P. Murugesan and J. A. Moses, Carbon quantum dots stabilized silver nanoparticles-based colorimetric sensor for detection of pesticide residues, Mater. Sci. Eng., B, 2024, 304, 117354.
103. R. Li, X. Mu, J. Xu and F. Zeng, Silicon quantum dots based fluorescent probes for detecting methyl parathion pesticide residues in potato, tap water and Yellow River, Spectrochim. Acta, Part A, 2025, 325, 125071.
104. M. Shaw, D. Samanta, M. A. S. Shaik, A. Bhattacharya, R. Basu, I. Mondal and A. Pathak, Solvent-induced switching between static and dynamic fluorescence quenching of N, S Co-doped carbon dots in sensing of Crotonaldehyde: A detailed systematic study, Opt. Mater., 2023, 137, 113600.
105. S. Bhunia, M. Mukherjee and P. Purkayastha, Fluorescent metal nanoclusters: prospects for photoinduced electron transfer and energy harvesting, Chem. Commun., 2024, 60(25), 3370–3378.
106. J. Sławski, R. Białek, G. Burdziński, K. Gibasiewicz, R. Worch and J. Grzyb, Competition between photoinduced electron transfer and resonance energy transfer in an example of substituted cytochrome c–quantum dot systems, J. Phys. Chem. B, 2021, 125(13), 3307–3320.
107. M. J. Deka, D. Chowdhury and B. K. Nath, Recent development of modified fluorescent carbon quantum dots-based fluorescence sensors for food quality assessment, Carbon Lett., 2022, 32(5), 1131–1149.
108. R. Pramanik, Nanomaterial-enhanced fluorescence sensors for dopamine neurotransmitters: a photophysical perspective, Anal. Methods, 2025, 17(21), 4251–4292.
109. X. Bai, L. Ga, Y. Du and J. Ai, Carbon quantum dot-based label-free fluorescent biosensor to detect E. coli, IEEE Sens. J., 2024, 24(16), 25284–25290.
110. X.-Y. Yue, Z.-J. Zhou, Y.-M. Wu, Y. Li, J.-C. Li, Y.-H. Bai and J.-L. Wang, Application progress of fluorescent carbon quantum dots in food analysis, Chin. J. Anal. Chem., 2020, 48(10), 1288–1296.
111. B. Zha, H. Li, S. Ren, J. R. Wu and H. Wang, Aggregation-Induced Emission (AIE) Probes in Fluorescent Sensing: Progress and Applications for Pesticide Detection, Appl. Sci., 2024, 14(19), 8947.
112. S. Shanmugaraju, K. Giriraj, A. Shanmughan, Y. Jegadeesan, M. K. Noushija, V. K. Alenthwar and U. Deivasigamani, Recent progress in fluorescence-based chemosensing of pesticides, Sens. Diagn., 2025, 4, 460–488.
113. A. Kaur, P. Kaur and S. Ahuja, Förster resonance energy transfer (FRET) and applications thereof, Anal. Methods, 2020, 12(46), 5532–5550.
114. P. I. Diriwari, Resonance energy transfer within and to optical nanoparticles for bioimaging and biosensing applications, Doctoral dissertation, Normandie Université, 2024.
115. M. Rani and U. Shanker, Fluorescence-based detection of thiamethoxam in agricultural and fruit samples by green synthesized N-CQDs from Citrus sinensis, J. Food Compos. Anal., 2025, 139, 107109.
116. D. Shrestha, A. Jenei, P. Nagy, G. Vereb and J. Szöllősi, Understanding FRET as a research tool for cellular studies, Int. J. Mol. Sci., 2015, 16(4), 6718–6756.
117. A. S. Sharma, S. Ali, D. Sabarinathan, M. Murugavelu, H. Li and Q. Chen, Recent progress on graphene quantum dots-based fluorescence sensors for food safety and quality assessment applications, Compr. Rev. Food Sci. Food Saf., 2021, 20(6), 5765–5801.
118. H. Xia, W. Zhang, Z. Yang, Z. Dai and Y. Yang, Spectrophotometric Determination of p-Nitrophenol under ENP Interference, J. Anal. Methods Chem., 2021, 2021(1), 6682722.
119. A. Kumaravel, S. Aishwarya and S. Sathyamoorthi, Emerging technologies for sensitive detection of organophosphate pesticides: a review, Curr. Anal. Chem., 2024, 20(6), 383–409.
120. D. Nautiyal and U. Jain, Emerging Trends in Fluorescent and Quenching Nanomaterials for Viral Detection: Innovations in Biological and Chemical Sensing, Talanta Open, 2025, 11, 100430.
121. N. Mahmoudi, F. Fatemi, M. Rahmandoust, F. Mirzajani and S. O. R. Siadat, Development of a carbon quantum dot-based sensor for the detection of acetylcholinesterase and the organophosphate pesticide, Heliyon, 2023, 9(9), e19551.
122. S. Tanwar, A. Sharma and D. Mathur, A graphene quantum dots–glassy carbon electrode-based electrochemical sensor for monitoring malathion, Beilstein J. Nanotechnol., 2023, 14(1), 701–710.
123. D. H. Nguyen, H. El-Ramady and J. Prokisch, Food safety aspects of carbon dots: a review, Environ. Chem. Lett., 2025, 23(1), 337–360.
124. K. Y. Chen, J. Kachhadiya, S. Muhtasim, S. Cai, J. Huang and J. Andrews, Underground ink: Printed electronics enabling electrochemical sensing in soil, Micromachines, 2024, 15(5), 625.
125. A. Murugesan, H. Li and M. Shoaib, Recent Advances in Functionalized Carbon Quantum Dots Integrated with Metal–Organic Frameworks: Emerging Platforms for Sensing and Food Safety Applications, Foods, 2025, 14(12), 2060.
126. H. W. Chu, B. Unnikrishnan, A. Anand, Y. W. Lin and C. C. Huang, Carbon quantum dots for the detection of antibiotics and pesticides, J. Food Drug Anal., 2020, 28(4), 539.
127. A. S. Rahmah, H. Heryanto, A. Rinovian, N. Yudasari and D. Tahir, Structural characterization of carbon quantum Dots derived from tea residue and their photocatalytic application in CQDs-modified Al2 (SO4) 3 nanoparticles for sustainable pesticide degradation, Mater. Chem. Phys., 2025, 334, 130401.
128. Y. Qu, L. Yu, B. Zhu, F. Chai and Z. Su, Green synthesis of carbon dots by celery leaves for use as fluorescent paper sensors for the detection of nitrophenols, New J. Chem., 2020, 44(4), 1500–1507.
129. J. Korram, P. Koyande, S. Mehetre and S. N. Sawant, Biomass-derived carbon dots as nanoprobes for smartphone–paper-based assay of iron and bioimaging application, ACS Omega, 2023, 8(34), 31410–31418.
130. L. Feng, X. Yue, J. Li, F. Zhao, X. Yu and K. Yang, Research Advances in Nanosensor for Pesticide Detection in Agricultural Products, Nanomaterials, 2025, 15(14), 1132.
131. B. Li, G. Xiang, G. Huang, X. Jiang and L. He, Self-exothermic reaction assisted green synthesis of carbon dots for the detection of para-nitrophenol and β-glucosidase activity, Arabian J. Chem., 2023, 16(7), 104820.
132. S. R. Lodha, J. G. Merchant, A. J. Pillai, A. H. Gore, P. O. Patil, S. N. Nangare and S. P. Patole, Carbon dot-based fluorescent sensors for pharmaceutical detection: Current innovations, challenges, and future prospects, Heliyon, 2024, 10(24), e41020.
133. A. Gholipour and S. Rahmani, The green synthesis of carbon quantum dots through one-step hydrothermal approach by orange juice for rapid, and accurate detection of dopamine, J. Fluoresc., 2024, 34(6), 2665–2677.
134. J. V. Kumar and J. W. Rhim, Fluorescence Probe for Detection of Malathion Using Sulfur Quantum Dots@ Graphitic-Carbon Nitride Nanocomposite, Luminescence, 2025, 40(2), e70112.
135. K. Deshmukh, V. Suvarna and R. Patel, Inner Filter Effect (IFE)-Based Fluorescent Sensing and Quantification of p-Nitrophenol (p-NP) Using N, S-Doped Carbon Dots (N, S-CDs), ChemistrySelect, 2025, 10(10), e202404933.
136. G. Pathiraja, C. D. Bonner and S. O. Obare, Recent advances of enzyme-free electrochemical sensors for flexible electronics in the detection of organophosphorus compounds: a review, Sensors, 2023, 23(3), 1226.
137. S. Tanwar, A. Sharma and D. Mathur, A graphene quantum dots–glassy carbon electrode-based electrochemical sensor for monitoring malathion, Beilstein J. Nanotechnol., 2023, 14(1), 701–710.
138. J. Xiong, C. Ma, H. Qu, H. Zhang, Q. He, Z. Zhao and H. Li, Recent Advances in Fluorescent Detection of Pesticides in Environmental and Food Matrices: From Molecular Probes to Nanoparticle-Based Sensors, J. Agric. Food Chem., 2025, 23783–23808.
139. Q. Li and Y. Fu, Brilliant cresyl blue modified carbon quantum dots for sequential detection of insecticides fipronil, Fe3+, and acephate, Microchem. J., 2025, 115170.
140. J. Fang, S. Zhuo and C. Zhu, Fluorescent sensing platform for the detection of p-nitrophenol based on Cu-doped carbon dots, Opt. Mater., 2019, 97, 109396.
141. B. Li, G. Xiang, G. Huang, X. Jiang and L. He, Self-exothermic reaction assisted green synthesis of carbon dots for the detection of para-nitrophenol and β-glucosidase activity, Arabian J. Chem., 2023, 16(7), 104820.
142. H. M. Hashem, M. El-Maghrabey, H. Borg, G. Magdy, F. Belal and R. El-Shaheny, Room-temperature upcycling of agricultural waste to carbon dots and its application as a selective fluorescence nanoprobe for iron (III) analysis in diverse samples, Talanta Open, 2025, 100484.
143. G. N. Kamel, R. A. Shabana, A. H. Hassan and R. El-Shaheny, Corchorus olitorius-Derived Green Carbon Dots: A Single Nanomaterial for Multiplexed Applications in Sensing, Catalysis, and Critical Micelle Concentration Analysis, Talanta, 2025, 128946.
144. Toxicological profile for phenol, NIH, National Library of Medicine, 2008, https://www.ncbi.nlm.nih.gov/books/NBK599456/table/ch7.tab2/?report=objectonly.
145. E. Te Brinke, A. Arrizabalaga-Larrañaga and M. H. Blokland, Insights of ion mobility spectrometry and its application on food safety and authenticity: A review, Anal. Chim. Acta, 2022, 1222, 340039.
146. A. Klimowska, E. Wynendaele and B. Wielgomas, Quantification and stability assessment of urinary phenolic and acidic biomarkers of non-persistent chemicals using the SPE-GC/MS/MS method, Anal. Bioanal. Chem., 2023, 415(12), 2227–2238.
147. H. B. Sousa, C. S. Martins and J. A. Prior, You don't learn that in school: an updated practical guide to carbon quantum dots, Nanomaterials, 2021, 11(3), 611.
148. J. G. López, M. Muñoz, V. Arias, V. García, P. C. Calvo, A. O. Ondo-Méndez and F. Fonthal, Electrochemical and Optical Carbon Dots and Glassy Carbon Biosensors: A Review on Their Development and Applications in Early Cancer Detection, Micromachines, 2025, 16(2), 139.

---