Size-based dynamics of nanoparticles in plant growth and environmental stress tolerance: potential benefits and hazards

Abstract

Environmental stress conditions such as drought, salinity, and heavy metal toxicity can considerably reduce growth and productivity of plants. Nanotechnology offers efficient solutions to enhance plant growth under stressful environments. Nanoparticles (NPs; 1–100 nm) in the form of plant growth promoters, nanopesticides, and nanofertilizers improve the nutrient use efficiency, stress resistance, and soil cleaning and minimize environmental pollution. Nanoparticles also transform plant–microbe associations through the modulation of rhizosphere microbial populations as well as root exudation, influencing the health of the plant as well as ecosystem services. Their nanoscale size and huge surface area facilitate enhanced physiological action and mobility as well as uptake within plant systems, frequently leading to enhanced growth and yield. However, these same traits can also cause toxicity. Therefore, it is important to carefully consider the NPs' size-dependent effects. This review highlights the significance of particle size in plant–NP interactions, with a particular emphasis on their dual potential to cause toxicity and mitigate environmental stress. This is, to the best of our knowledge, the first thorough evaluation of size-dependent NP effects on plants and related microbes. The significance of creating safe, optimized nanomaterials that provide agronomic advantages with little ecological risk is also highlighted.

---

Environmental significance

The size of nanoparticles (NPs) is critical in determining their impact on plant growth and environmental stress tolerance. Small NPs possess greater mobility, uptake, and plant physiological activity that influence growth. Due to high surface-area-to-volume ratio, a larger fraction of atoms or functional groups are exposed at the surface, which enhances surface chemistry reactions and electron interactions, thereby increasing reactivity and, consequently, phytotoxicity risk. Small NPs can generate excess ROS, causing oxidative stress, cell damage to plants, and modification of plant metabolic processes. Therefore, size-dependent beneficial and adverse effects information is significant to the safe and optimized formulation of NPs with low environmental hazard and maximum agronomic efficacy.

1. Introduction

Environmental stresses like salinity, water stress, high and low temperatures, and heavy metal toxicity are the major yield- and growth-limiting factors in plants. Nanoparticles (NPs), due to their small size (1–100 nm), possess unique physical and chemical traits, like high surface-to-volume ratio and heightened reactivity that can enhance crop growth under normal and environmental stress conditions. Their adjustable pore size, specially designed carrier surfaces, and precise release control make them ideal for creating nanofertilizers, nanopesticides, nanobiostimulants, and plant growth regulators.^1,2 Nanoparticles help plants handle stress by triggering antioxidant defenses, fine-tuning stress signals, and managing osmolyte buildup to reduce damage from harsh environmental conditions.^3,4 Nanoparticles help restore polluted or nutrient-poor soils by boosting root function and nutrient absorption.⁵ In addition, NPs are able to modify microbial communities in the rhizosphere and patterns of root exudation, increasing plant–microbe association and tolerance to stress.⁶ Accordingly, nanomaterials are the substitute sustainable options for traditional inputs with the added advantages of saving resources.⁷

To understand NPs' interaction with plants, it is important to understand their size-dependent behavior, which governs their uptake, translocation, and impact on plant physiology.^8–10 The small size of NPs facilitates their easier penetration across biological barriers into cell compartments that are not accessible for larger-sized particles.¹¹ Smaller sizes cause better seed germination, root growth, and plant growth compared to larger ones.^12,13 Smaller particles are also more efficient in promoting photosynthesis, antioxidant activity, and fruit quality under stress conditions than larger particles.¹⁴ However, the size-dependent behavior of NPs is also a critical factor in determining potential toxicity in plants. Smaller NPs are more toxic as they can trigger cellular membrane damage, block nutrient channels, and cause oxidative stress.^15,16 The size-, shape, dose-, particle type-, plant species-, and environment-dependent nature of nanoparticle (NP) behavior underscores the importance of proper assessment of NP formulations to balance their benefit with risk.

Despite this growing number of research studies, essential gaps in the understanding of the size-dependent effects of NPs on plant growth and physiology under environmental stress have yet to be addressed. Critical questions still remain regarding size-dependent uptake, translocation, and modes of NP interactions with cell components and long-term effects of their application in agroecosystems. These gaps must be filled in order to create safe and effective NP-based solutions that will increase crop yields while minimizing possible dangers to crops and the environment. To the best of our knowledge, this is the first review on the size-dependent dynamics of NPs in plants. This review examines how they affect plant physiology, stress response, associated microorganisms and overall development. It critically assesses current studies and offers insights into the creation of sustainable nano-agrochemicals.

2. Regulating the size of NPs

Nanoparticle size can be controlled by an interplay of chemical (i.e., pH, surfactants, stabilizers), physical (e.g., laser ablation, sputtering), biological, mechanical, and post-synthesis methods. Through the use of these methods in combination with one another, NPs of the desired size can be prepared, and their performance in application can be maximized.

2.1. Chemical methods

Chemical procedures provide tunable and scalable pathways for NP size management. Important parameters like reaction temperature, pH, precursor amount, and presence or absence of surfactants or capping agents directly control nucleation and growth rates.^17–19 Temperature also greatly affects the NP size during synthesis and hence is a significant parameter to manage their characteristics.^20,21 Nanoparticle synthesis generally involves two predominant steps: growth and nucleation. Based on the classical LaMer model, nucleation corresponds to the formation of small clusters via the rapid growth of precursor molecules, and growth corresponds to the attachment of atoms or monomers to nuclei. Increased temperature enhances supersaturation, and consequently the nucleation rate is enhanced. This results in the creation of an abundance of nuclei within a limited span of time, reducing the amount of precursor material left per particle. Thus, NPs generated at elevated temperatures are smaller in size.^22,23 In contrast, decreasing temperature decelerates nucleation and allows more time for growth within present particles. This tends to produce fewer, larger NPs as well as a more heterogeneous size distribution due to dissimilar growth rates.²⁴ Temperature is also a controlling factor in reaction kinetics, solubility of the precursor, and rate of diffusion, all with a direct influence on particle ultimate size as well as on homogeneity. Experimental evidence confirms this relationship. For instance, raising the temperature of the chemical reduction approach to the synthesis of silver nanoparticles (Ag NPs) from 30 °C to 80 °C decreased the average particle size from about 50 nm to about 15 nm.¹⁷ Likewise, gold nanoparticles (Au NPs) prepared at 25 °C were approximately 30 nm in diameter, but those prepared at 80 °C were approximately 10 nm of the same spherical shape.²⁵ Overall, temperature plays a significant role in the synthesis of NPs. High temperature favors fast nucleation and the formation of small particles, but low temperature favors slow nucleation and prolonged growth to form large particles. Effective temperature control is therefore critical in the synthesis of NPs of specified size and characteristics.

The pH of the synthesis medium is instrumental in controlling NP size by affecting nucleation, growth, and stabilization processes. pH has a strong influence on chemical equilibria, precursor ionization, redox potential, and NP surface charge.^18,19 pH modification can alter the charge and reactivity of functional groups used during synthesis. This, in turn, changes nucleation rates and particle stabilization.²² In acidic pH, protonation of reactants reduces nucleation such that fewer, larger particles result. Basic conditions, on the other hand, generally increase nucleation and reduce particle size through the formation of more nuclei.²⁴ pH also controls the surface zeta potential of NPs, which determines interparticle repulsion. At optimum pH values, particles receive sufficient electrostatic repulsion to prevent aggregation and produce an even particle size distribution.²³ Deviations from the optimum pH range lower stability to result in agglomeration or flocculation, leading to an increase in particle size. Experimental evidence supports such trends. In sol–gel synthesis of zinc oxide nanoparticles (ZnO NPs), pH 10–11 produces smaller and more monodisperse particles compared to acidic conditions.²⁶

Functionalization, either during or after the synthesis of NPs, plays a remarkable role in affecting not just surface properties but even the size of NPs. It does so directly, by adding either layers or coatings to the surface, or indirectly, by preventing agglomeration and facilitating proper dispersion.^27,28 Greater dispersion by functionalization can hinder particle agglomeration, which otherwise leads to greater apparent particle size and lower surface-to-volume ratio.^29,30 Zinc oxide nanoparticles, for instance, are susceptible to agglomeration by intermolecular forces, which reduce their effective surface area. Functionalization reduces these interactions, improving small effective particle sizes and bioavailability.^31,32 Typical functional groups, including amines, silanes, thiols, and polymers, participate in covalent or non-covalent interactions (e.g., van der Waals forces, hydrogen bonding), which help in size stabilization and improved colloidal stability.^33,34 Application of bioactive molecules such as proteins, sugars, and amino acids as surface modifiers not only contributes to functional properties but also alters hydrodynamic size, with enhanced uptake and transport across biological systems.^35,36 Scanning electron microscopy (SEM) imaging of 3-aminopropyl trimethoxysilane (APTES)-functionalized magnetic iron oxide nanoparticles (Fe₃O₄ NPs) indicated a small increase in particle diameter at each step of functionalization, confirming that surface coating materials contribute to particle thickness without affecting core geometry.³⁷ Similarly, hydrothermal in situ functionalization has extremely precise control over NP size, shape, and crystallinity.³⁸ In addition, amino acid (such as proline and tryptophan)-coated NPs exhibit changed particle sizes and increased solubility, which is beneficial for biomedical or agricultural delivery systems through increased cellular uptake and decreased cytotoxicity.^39,40

For agricultural applications, functionalized carbon quantum dots (such as Put-CQD NPs) and proline- or sugar-functionalized graphene oxide (GO) and silicon nanoparticles (Si NPs) exhibited enhanced dispersibility and cellular translocation. These alterations are responsible for more consistent particle sizes and better performance under conditions of stress.^41–43 Surface functionalization, overall, alters NP size directly by increasing surface layers and indirectly by avoiding agglomeration, stabilizing dispersion, and inducing bioactivity. These surface and size behavior alterations are crucial to establishing the efficacy, safety, and usability of NPs in most applications.

Surfactants are of crucial importance in the synthesis of NPs as they regulate crystal growth and precise control of particle size and shape. Surfactants are amphiphilic and therefore contain hydrophobic and hydrophilic groups, facilitating their adsorption on the growing surface of NPs. This adsorption makes it feasible to limit uncontrolled growth and aggregation of particles.^18,19 Surfactants like cetyltrimethylammonium bromide (CTAB), sodium dodecylbenzenesulfonate (SDBS), and polyethylene glycol (PEG) and stabilizers like polyvinylpyrrolidone (PVP), citrate, thiols, and polymers are commonly used to stabilize NPs in solutions. They stabilize NPs by creating steric or electrostatic repulsion between different particles, thereby preventing agglomeration. This is especially crucial on the nanoscale, where high surface energy can lead to uncontrolled and rapid particle growth or agglomeration.^23,24 Their effectiveness relies greatly on the synthesis conditions, for example, pH and temperature. Cetyltrimethylammonium bromide is commonly employed in the synthesis of gold (Au) and silver (Ag) NPs, wherein it not only stabilizes the nanocrystals but also controls the growth of anisotropic particles such as rods and prisms by adsorbing preferentially on particular facets.²⁶ Similarly, citrate was useful as a capping as well as a reducing agent during Au NP synthesis to assist towards the formation of small and monodisperse spherical NPs.⁴⁴ In another study, citrate reduction resulted in the production of decreased-size Au NPs at alkaline pH due to enhanced nucleation and stabilization.⁴⁵ Moreover, pH management along with the use of a surfactant or stabilizer such as CTAB, PVP, citrate, or thiols can also assist towards controlling NP size effectively and avoiding aggregate formation. Surfactants have the capability to bind very strongly to the surface of NPs, preventing their growth and leading to small particle size and low polydispersity index (PDI).⁴⁶ Chin et al. (2011) prepared starch NPs by precipitation of a solution of sago starch dissolved in absolute ethanol under controlled conditions. Surfactant-added synthesis lowered the mean particle size considerably.⁴⁷ With CTAB, the particle size was reduced to 250–300 nm, while Tween 80 produced smaller particles of 150–200 nm. Masoudipour et al. (2017) reported a comparison of the effect of surfactants CTAB, SDBS, and PEG used in ultrasonic treatment.⁴⁸ Dropwise addition reduced particle size and stabilized the NPs. Optimal concentrations of 1% (w/v) SDBS and 0.5% (w/v) CTAB gave particle sizes of 182.2 nm and 236.1 nm, respectively. In combination with optimal pH and temperature, utilization of surface-active agents gives better reproducibility, enhanced colloidal stability, and improved control over the final NP size distribution. Thereby, surfactant-assisted synthesis can be effectively used in NP design for targeted uses.^18,19

2.2. Biological methods

Green synthesis routes, or biological methods, employ the usage of plant extracts, enzymes, fungi, or bacteria for metal ion reduction to NPs.⁴⁹ These routes tend to provide comparatively monodisperse NPs. By changing parameters like concentration of extract, incubation period, and type of biomass, the size of produced NPs can be controlled.^50–52 Microbe-mediated construction products involve their inherently sophisticated biochemical machinery, which leads to well-defined NPs of different chemical compositions, shapes, and sizes.⁵³ Plant extracts have been found to be more effective than microbial systems in the synthesis of NPs because they can reduce metal ions at a faster rate and yield highly stable nano-sized materials.^54,55 This is brought about by the wide variety of bioactive compounds found in plants, such as alkaloids, flavonoids, phenols, tannins, and alcohols, which have both reducing and stabilizing properties when used in the process of NP synthesis.^56,57

The nature of various plant species or the proportion of extract to metal precursors may alter the size distribution substantially.⁴⁹ The growth temperature, extraction time, synthesis temperature, concentration of silver nitrate (AgNO₃), and, above all, exposure to light controlled the size of Ag NPs prepared with Saccharomyces cerevisiae DSM 1333 cell-free extract.⁵⁸ White light had a significant impact on increasing NP yield and decreasing particle size during this biological method of synthesis. Irradiation with light caused a 30 nm blue shift of the UV-vis absorption peak from 440 nm to 410 nm, corresponding to particle sizes of 130 nm and 100 nm, respectively. This is an indication of the formation of smaller NPs than those synthesized in the dark.⁵⁸ Gold colloids of different sizes were synthesized by varying the volume of Trigonella foenum-graecum L. (fenugreek) seed extract added to a chloroauric acid solution. The quantity of extract and pH were important factors determining the size distribution of Au NPs. The NPs are more stable at pH 6 and 7.⁵⁹ Likewise, plant-mediated synthesis of Ag NPs has indicated that alkaline pH produces smaller spherical particles, whereas acidic pH produces larger polydisperse particles owing to a slower rate of reduction.⁴⁴ Overall, the biological method is an eco-friendly approach that holds great promise for diverse applications by enabling controlled NP synthesis of different sizes while minimizing toxicity and environmental impact.

Thus, biological methods offer a sustainable and versatile approach to NP synthesis, combining environmental safety with cost-effectiveness while enabling precise control over particle size, shape, and stability, making them highly suitable for agricultural, biomedical, and industrial applications.

2.3. Physical methods

Nanoparticle size can be effectively controlled using physical methods such as laser ablation, evaporation–condensation, and sputtering. In laser ablation, a pulsed laser vaporizes a solid target in a liquid medium, and parameters such as laser energy, pulse duration, and solvent properties allow precise control over particle size.⁶⁰ While this method produces highly pure NPs, it is limited by low yields and scalability.⁶¹ Evaporation–condensation involves heating a material to form vapors, followed by controlled cooling in a carrier gas. Factors like temperature gradients, evaporation rate, inert-gas pressure, and gas flow rate influence nucleation and growth, thereby determining NP size.⁶² Rapid and programmed condensation of evaporated molecules helps achieve the desired size distribution. Although effective in achieving narrow size distributions, this method requires high energy input and is more suited for laboratory-scale production.

Sputtering, typically used in thin-film deposition, can be adapted for NP synthesis without involving chemical reactions. In this method, metals are sputtered into a capture medium with extremely low vapor pressure, enabling the formation of NPs.⁶³ Size control can be achieved by adjusting the capture medium's composition and temperature. Additionally, sputtering parameters such as applied voltage, current, and substrate conditions significantly influence particle size. Lower target temperatures and higher voltages are particularly effective for producing smaller, size-controlled NPs.⁶³ However, the method demands expensive vacuum equipment and may face limitations in large-scale NP recovery.

Chemical vapor deposition (CVD) and microemulsion methods offer other methods of NP size control. During CVD, gas-phase precursors are decomposed on a substrate under elevated temperatures to produce NPs, whose size is governed by temperature, pressure, and gas flow. Interestingly, decreasing pressure in the condensation chamber has been identified to deliver silicon nitride (Si₃N₄) NPs of reduced size.⁶⁴ Chemical vapor deposition enables uniformity and scalability, although it often requires toxic precursors and high operational costs. Microemulsions, thermodynamically stable mixtures of oil, water, and surfactant, are nanoscale reaction media where droplets are nanoreactors. The size of droplets dictates the size of NPs mainly, and that is based on the surfactant composition and concentration. Size is mainly dictated by the number of micelles and available precursor ions. In particular, the amount of NPs is consistent with the amount of micelles, and their ultimate size is a function of both the number of nuclei that have formed and the overall material to be used for nanocrystal growth. This information allows for precise control over synthesis conditions to produce NPs of desired sizes.⁶⁵ While this approach offers precise control, it relies heavily on surfactant use, which complicates purification and raises environmental concerns.

Each synthesis route offers distinct advantages and limitations; physical methods such as laser ablation and sputtering provide high purity and precise control but face challenges in scalability and cost, whereas chemical methods like CVD and microemulsions enable fine size regulation with greater potential for scale-up but may involve complex setups, surfactants, or toxic precursors. Careful selection of the method thus depends on the balance between purity, yield, scalability, and environmental considerations.

2.4. Mechanical methods

Ball milling and high-pressure homogenization are top-down mechanical methods that grind bulk materials into NPs. While such methods can initially produce wide size distributions, optimizations like limiting the milling time or employing sieving and centrifugal classification can then successfully limit the size range. Ball milling particle size can be managed by varying parameters like milling time, speed, ball size, and grinding medium-to-material ratio. This process, discovered by John Benjamin in 1970, is extremely effective in the production of bulk powders, particularly metal oxides and ceramics, into NPs by high-energy collision.⁶⁶ It is based on the process of application of mechanical stress for decreasing the size of the particle as well as modifying the surface characteristics. Mechanical milling can be classified as high energy or low energy based on the collision intensity and energy transfer to the powders. High-energy milling uses faster mill speeds and intense impacts for rapid particle size reduction and alloying, while low-energy milling involves gentler impacts suited for mixing or blending without extensive particle deformation.⁶⁷ High-pressure homogenization, however, subjects material to high pressure through thin gaps. This brings the material to the nanoscale range. One effective process employing this process, along with water-in-oil miniemulsion, cross-linking has been employed in synthesizing sodium trimetaphosphate-cross-linked starch NPs. Spherical, monodisperse, and stable NPs were synthesized. They were largely affected in size by factors like the concentration of surfactants, water/oil ratio, starch content, pressure during homogenization, and the number of cycles of processing.⁶⁸

2.5. Post-synthesis processing

Post-synthesis treatment processes like ultrasonication, centrifugation, and filtration are efficient for size refinement of NPs.^69,70 Sonication is among the simplest and most efficient methods for modifying the size of NPs. Sonication decreases particle size by breaking up large nanoclusters, and duration of sonication has a significant influence.⁷¹ Tombuloglu et al. (2024a) synthesized a hard/soft nanocomposite (CoFe₂O₄/Ni_0.8Cu_0.1Zn_0.1Fe₂O₄) via sonochemical routes at two sonication durations of 20 and 60 min.⁷⁰ Increased sonication decreased the average particle size from 26.7 nm (20 min) to 17.4 nm (60 min). Ultrasonication utilizes acoustic energy for the breaking of agglomerates, thus giving more dispersion and reducing the effective particle size. This de-agglomeration is also brought about, to a considerable extent, by cavitation, depending on the hydrostatic pressure of the medium, the acoustic amplitude of the sound wave, and the presence of gas in the dispersion medium, all of which affect the intensity of cavitation and thus the efficiency of the process.⁷² Centrifugation separates NPs according to their rate of settling, and higher centrifugal power and longer time ensure separation of the smaller particles.⁷³ For instance, Au and Ag NPs prepared from Magnolia kobus (kobus magnolia) extract were efficiently separated by density gradient centrifugation, where size ranges were around 52–117 nm for Au and 38–61 nm for Ag, increasing mean particle size with increasing sucrose concentration per layer. Thicker, thin plate-shaped Au NPs precipitated in higher-density sediments, and thinner spherical particles precipitated in lower-density gradients. Silver nanospheres of different sizes were also recovered from different densities, and fewer plate-type particles were obtained in lighter fractions.⁷⁴ Size-based separation of NPs can be achieved by filtration through nanoporous membranes effectively when uniformity is an issue. Freeze-drying resulted in agglomeration and an increase in particle size, whereas the incorporation of a cryoprotectant such as D-trehalose combined with ultrasonication decreased particle size. However, extended ultrasonication resulted in size increase, suggesting that there has to be some limit beyond which additional introduction of energy may reverse the process.⁷⁵ Conventional techniques such as ultracentrifugation, chromatography, filtration, electrophoresis, and selective precipitation are generally batch processes, involving multiple preparatory steps and enormous sample sizes. Mimicking dynamic fluid flows in microfluidic devices enhances reproducibility and control by creating precise and consistent mixing conditions that regulate nucleation and growth of NPs. This leads to uniform reaction environments, efficient mass transfer, and well-defined residence times, enabling the synthesis of NPs with narrow size distributions and tailored properties.^76,77 In most cases, with the integration of various methods like chemical, physical, or biological synthesis pathways and following methodologies like ultracentrifugation, electrophoresis, filtration, chromatography, selective precipitation, and microfluidic separation, precise control over NP size, shape, and stability can be achieved to suit application requirements.

3. Influence of NP size on their uptake, translocation, and accumulation in plants

Particle size greatly affects the uptake and translocation of nanomaterials in plants. Generally, smaller NPs have greater uptakes and translocations than larger particles. The particle size of NPs significantly determines the manner in which they absorb, migrate through, and accumulate in plant tissues. Their behavior in all these manners, based on their particle size, affects the safety and efficacy of the application of NPs in agriculture directly. They are more bioavailable and possess better translocation than their larger counterparts.⁷⁸ The large particles tend to agglomerate and are not mobile in plant systems. Experiments have proved that smaller NPs are absorbed and conveyed better in roots and transferred to shoots by various plant species. For example, Kim et al. (2024) noted that 10–30 nm ZnO NPs accumulated more in the leaves of Brassica chinensis L. (bok choy) compared to 300 nm particles, which were less mobile but more toxic.⁷⁹ Large ZnO NPs have low root-to-leaf translocation, which may be because they are larger and have aggregation characteristics. Bioconcentration factor (BCF) is defined as the ratio of the concentration of a chemical substance in an organism to its concentration in the surrounding environment, indicating the extent of chemical accumulation in the organism's tissues. Bioaccumulation studies showed that ZnO NPs (10–30 nm) exhibited significantly higher bioconcentration factors (BCF values ranging from 3 to 6) compared to larger particles. Translocation factor (TF) is defined as the ratio of the concentration of a substance, such as a nanoparticle or metal, in the aerial parts (e.g., leaves or shoots) of a plant to its concentration in the roots. Translocation factor was smaller for larger particle sizes (0.3–1), proving decreased mobility of larger-sized ZnO NPs in the plant. Micro X-ray fluorescence analysis (μ-XRF) with the possibility of elemental mapping demonstrated zinc (Zn) spatial distribution in leaf tissues. For 10–30 nm ZnO NP and Zn ion treatment, Zn was found to localize predominantly at the leaf edges. However, exposure with 300 nm ZnO NPs resulted in Zn accumulation primarily in the primary and secondary veins and petioles. Bio-transmission electron microscopy (TEM) imaging showed 10–30 nm ZnO NPs and NP aggregates in vacuoles, plasma membranes, and organelle membranes in cells along the leaf margin. Yusefi-Tanha et al. (2024) demonstrated that smaller copper oxide nanoparticles (CuO NPs) of 25–50 nm diameter accumulated in greater amounts in the roots of Glycine max L. (soybean) compared to larger particles (250 nm).⁸⁰ Uptake of ceria NPs in Cucumis sativus L. (cucumber) existed in a particle size-dependent form. Smaller ceria NPs (7 and 25 nm) were easier to absorb via the roots and translocate into leaves in comparison to 100 nm particles.⁸¹ Consistent with this trend, Ma et al. (2010) showed that cerium oxide nanoparticles (CeO₂ NPs) smaller than 7 nm were absorbed by cucumber plants and translocated to the shoots, whereas larger particles remained confined to the roots.⁸² For titanium dioxide nanoparticles (TiO₂ NPs), only the finest particles can translocate throughout the whole Triticum aestivum L. (wheat) plant. Larue et al. (2012) observed that NPs smaller than 140 nm can penetrate the root epidermis, and those smaller than 36 nm can pass through the root parenchyma and translocate from root to shoot.⁸³ Wang et al. (2025) examined the influence of various ZnO NP sizes (0, 30, 50, and 90 nm) on Agrostis stolonifera L. (bentgrass) via soil drenching.⁸⁴ Based on this work, 30 nm ZnO NPs caused higher Zn content in bentgrass root and leaf tissues at the concentrations of 186 mg kg⁻¹ and 294 mg kg⁻¹, respectively, when compared to 50 nm and 90 nm sizes. Surprisingly, SEM mapping deduced Zn content in leaf tissue was higher than Zn content in root tissue. Furthermore, Zn content was higher at 30 nm size, with up to 0.3 wt% Zn in root tissue and up to 2.4 wt% in leaf tissue. The research confirmed the translocation of ZnO NPs from root tissue to aerial leaf tissue. High particle deposition was seen in leaf and root cells exposed to ZnO NPs with sizes of 30 to 90 nm. Notably, 30 nm ZnO NPs were penetrating through the cell membrane from the root to leaf tissue. Under treatment with 30–90 nm ZnO NPs, the root and leaf cell structure was found to be intact with normal vacuoles and plasma membranes. However, 30 nm and 50 nm ZnO NP exposure induced cytoplasmic turbidity by ZnO NPs entrapped in cells.⁸⁵ Notably, the larger 90 nm ZnO NPs were unable to pass through the membrane transport due to their size, highlighting NP size as a critical factor in regulating root-to-leaf long-distance transport.⁸⁴ Li et al. (2023b) ascertained that there was higher bioaccumulation of NPs in Oryza sativa L. (rice) root vascular tissues in the case of smaller ZnO NPs (5, 20, and 50 nm) compared to 100 nm ZnO NPs, as verified by laser ablation inductively coupled plasma optical emission spectroscopy (LA-ICP-MS) and bio-TEM.⁸⁵

These findings indicate that NP size is a key factor influencing their uptake, translocation, and accumulation in plants. Better results are achieved from smaller NPs with higher translocation capability up to inner plant tissues. Nevertheless, their high surface reactivity is of concern as they can cause oxidative stress and toxicity at high doses. Therefore, precise selection and optimization of NP size are essential to achieve maximum agricultural benefits with the least possible risks to plants and the environment.

4. Size-based impacts of NPs on plants under stress

Nanoparticles are increasingly applied in agriculture due to their high surface area and size tunability characteristics. Of these, size is of utmost significance in determining NPs' interaction with plants. Size determines the uptake, mobility, accumulation, and biological effect on plant systems. Small NPs are more easily able to penetrate through cell walls and membranes and enter inner tissues and even organelles of cells, and hence influence metabolic processes, growth habits, and stress reactions. Larger NPs are, however, limited to the root surface or apoplast with limited transport within. Table 1 shows the size-dependent effects of NPs on plant systems.

Table 1 Size-dependent effects of nanoparticles on plants

Nanoparticle type	Size	Mode of application	Plant species	Stress	Observed effect	Reference
Ag NPs	10 nm, 30–60 nm	Soil	Triticum aestivum L.	—	Smaller Ag NPs had limited effects on the microbiome, while larger Ag NPs enhanced beneficial, plant growth-promoting microbes	107
Ag NPs	8 nm (spherical), 45 nm (decagonal), 47 nm (pyramidal)	Nutrient solution	Arabidopsis thaliana L.	—	45 nm and 8 nm induced lowest and highest root inhibition and Cu/Zn SOD accumulation, respectively	97
Ag NPs	68.6 nm, 77.5 nm, 98.9 nm, 111.7 nm	Seed soaking	Oryza sativa L. Zea mays L.	—	68.6 nm caused highest protein content in rice and maize	88
Al2O3 NPs	5 nm, 30–60 nm, 135 nm	—	Glycine max L.	Flood	30–60 nm promoted root length, regulated ascorbate glutathione cycle and enhanced abundance of voltage-dependent anion channel protein, 135 nm increased mitochondrial membrane permeability. 5 nm increased isocitrate dehydrogenase	106
CeO2 NPs	7 nm and 25 nm	Nutrient solution	Cucumis sativus L.	—	7 nm showed better uptake and translocation than 25 nm	81
CoFe2O4/Ni0.8Cu0.1Zn0.1Fe2O4 NCs	26.7 nm, 17.4 nm	Hydroponics	Triticum aestivum L.	—	26.7 nm enhanced root length and micronutrient uptake	70
CuO NPs	25 nm, 50 nm, 250 nm	Soil drenching	Glycine max L.	—	25 nm caused maximum inhibition of chlorophyll a and b, grain yield, nutrients; increased H2O2 and MDA; enhanced SOD and CAT	80
CuO NPs	20–50 nm	Soil amended	Glycine max L.	—	50 nm significantly improved biomass over 20 nm	100
Fe2O3 NPs	8–10 nm, 20–40 nm, 30–50 nm	Hydroponics	Triticum aestivum L.	—	20–40 nm enhanced root length, biomass and chlorophyll	87
Fe3O4 NPs	10 nm, 100 nm	Nutrient medium	Hordeum vulgare L.	—	100 nm improved germination, 10 nm elevated H2O2, CAT, and membrane damage	16
NaYF4:Yb^3+, Er^3+@NaYF4	26 nm, 52 nm	Seed treatment	Triticum aestivum L.	—	26 nm increased root and hypocotyl mass, 52 nm inhibited growth	115
PbO2 and PbO NPs	10 ± 3 nm (PbO2), 20 ± 5 nm (PbO)	Hydroponic treatment	Zea mays L.	—	10 nm promoted better elemental transfer from root to shoot; particle size influenced toxicity and uptake	85
Se NPs	10 nm, 50 nm	Foliar	Punica granatum L.	Drought	10 nm was more effective in increasing pigments, and antioxidant activity	14
Si NPs	30 nm, 50 nm, 100 nm	Solution	Allium cepa L.	—	50 nm Si NPs were relatively non-toxic, highest mitotic index, lowest chromosomal aberrations, reduced ROS accumulation	111
Si and mesoporous silica NPs	Si NPs 160 nm, MSNPs 100 nm	Foliar spray	Glycine max L.	Biotic stress (S. litura larvae)	Both sizes effectively upregulated jasmonic acid defense genes	116
TiO2 NPs	23 nm, 120.7 nm, 154.3 nm, 485.7 nm	Solution	Oryza sativa L.	—	485.7 nm increased shoot and root length, smaller sizes toxic at higher concentrations	86
TiO2 NPs	14–655 nm	Suspension	Triticum aestivum L.	—	<140 nm accumulated in roots, <36 nm moved to shoots	83
TiO2 NPs anatase (NAnT), pristine rutile (NRuT), hydrophilic rutile (NLRuT), hydrophobic rutile (NBRuT)	25.22 nm (NAnT), 33.10 nm (NRuT), 40.89 nm (NLRuT), 39.61 nm (NBRuT)	Nutrient solution	Oryza sativa L.	Pb toxicity	Only smallest NAnT entered roots via apoplastic route; smaller size enhanced Pb bioaccumulation reduction	117
ZnO NPs	18 nm, 35–45 nm, 80–200 nm	Foliar	Beta vulgaris L.	—	35–45 nm increased fresh weight and protein, 80–200 nm enhanced chlorophyll	99
ZnO NPs	5–50 nm, 50–100 nm	Nutrient solution	Oryza sativa L.	—	5–50 nm reduced growth and increased MDA	110
ZnO NPs	20 nm,100 nm (hydrophilic), 20 nm (hydrophobic)	Nutrient medium	Vigna radiata L.	—	Hydrophilic 20 nm inhibited root elongation, hydrophobic ZnO showed lower toxicity	98
ZnO NPs	10 nm, 50 nm, 100 nm, 200 nm, 300 nm	Soil drenching	Brassica campestris L.	—	300 nm most toxic, smaller sizes showed greater translocation	79
ZnO NPs	30 nm, 50 nm, 90 nm	Soil drenching	Agrostis stolonifera L.	—	50 nm ZnO NPs induced most optimal physiological and biochemical responses, enhanced growth and antioxidant enzyme activities	84

---

It is critical to understand these size-dependent effects for the safe and effective use of NPs in agriculture. Proper engineering of NPs can improve nutrient delivery, pathogen protection, or stress tolerance in plants. Improper size choice, however, can result in toxicity or loss of efficacy. For that purpose, it is critical to tailor NP size in a manner where maximum benefits can be realized without maximum risk in plant-based applications.

4.1. Photosynthesis and growth

The dimensions of NPs play a major and complex role in controlling photosynthesis and plant growth by altering surface area, reactivity, and plant system interaction. Nanoparticle size affects the rate of photosynthesis and pigment concentration. The results affirm the necessity of strict attention to size as well as dose in employing NPs in promoting plant growth or stress tolerance. The study has revealed that the concentration and size of NPs control the effect of NPs on photosynthesis. Tombuloglu et al. (2024b) reported that small-sized Fe₃O₄ NPs (10 nm, NP10) at 50 mg L⁻¹ greatly increased the chlorophyll a, chlorophyll b, and carotenoid contents in leaves. In contrast, in the case of large NPs (100 nm, NP100), no significant increase was observed at the lower doses (50 and 100 mg L⁻¹), but pigmentation improved only at the higher dose of 200 mg L⁻¹.¹⁶ This was considered an indication that the smaller particles were readily absorbed and translocated to the cells, thus more efficiently activating the photosynthetic pigments even at lower concentrations. Zahedi et al. (2021) demonstrated in an experiment that selenium nanoparticle (Se NP) application through leaves affected the concentration of photosynthetic pigments in Punica granatum L. (pomegranate) under drought stress remarkably.¹⁴ Selenium nanoparticles of size 10 nm were more efficient compared to 50 nm Se NPs, reflecting size-dependent enhancement of chlorophyll content as well as photosynthesis ability of stressed plants. In contrast, Theerak et al. (2023) discovered that larger-sized TiO₂ NPs (490 nm) induced greater growth and chlorophyll content in rice than 23 nm and 100 nm NPs. This could be due to reduced reactive oxygen species (ROS) formation, cellular intrusion and aggregation compared to 100 nm and 23 nm.⁸⁶

Iron(III) oxide nanomaterials of different sizes (8–10, 20–40, and 30–50 nm) greatly improved chlorophyll content, root growth, plant growth, and total biomass, reflecting heightened photosynthetic performance and vigor. The 20–40 nm NPs proved most growth-promoting among the sizes tested, likely because they offered superior absorption and translocation in plant tissues. The increased accumulation of iron (Fe) also justified enhanced physiological performance. These results demonstrate that Fe₂O₃ NPs, especially 20–40 nm, are a promising nanofertilizer for stimulating photosynthesis and plant growth in crops.⁸⁷ In contrast, Yusef-Tanha et al. (2024) revealed that among nCuO of three different sizes, 25 nm (small, S), 50 nm (medium, M), and 250 nm (large, L), with identical surface charge, strongest inhibition was observed in the case of 25 nm nCuO, where levels of chlorophyll a and chlorophyll b decreased by 75% and 61.5%, respectively.⁸⁰ Interestingly, carotenoid content had an opposing trend; nCuO-S dramatically enhanced carotenoid content by a 2.5-fold difference compared to the control. Carotenoids were not found to have any notable difference between medium and large nCuO sizes or copper (Cu²⁺) treatment.

Phytogenic Ag NPs, synthesized using Stevia rebaudiana Bertoni (candyleaf) leaf extract, exhibited clear size-dependent effects on seed germination, growth, and physiological traits in rice, Zea mays L. (maize), and Arachis hypogaea L. (peanut).⁸⁸ Four Ag NP treatments (S1–S4) varied in synthesis parameters and particle sizes (ranging from 68.6 to 111.7 nm). While all treatments achieved 100% germination in peanuts, only moderately sized Ag NPs (S3: 68.6 nm and S4: 98.9 nm) significantly improved germination in maize and rice compared to bulk Ag and control. Growth responses were generally positive, though rice treated with S1 (77.5 nm) showed reduced shoot and root development. Chlorophyll and carotenoid responses varied by species and NP size. In rice and maize, S3 and S4 enhanced chlorophyll a/b ratios and carotenoid content, indicating improved photosynthetic efficiency and photoprotection. Conversely, in peanuts, higher carotenoid levels under S1 and S4 suggested increased stress. Notably, S3 consistently outperformed bulk Ag, implying that intermediate-sized Ag NPs can optimize plant physiological responses while minimizing stress.

In general, small NPs (10–20 nm), such as TiO₂ NPs around 7–14 nm, enhance electron transport and photosynthesis by penetrating chloroplast membranes, but very small ZnO NPs (5–10 nm) can elevate lipid peroxidation, reducing photosynthetic output due to very high reactivity. Medium-sized NPs (20–50 nm) improve chlorophyll content, photosynthesis, and protein accumulation, promoting biomass and photosynthetic efficiency. Larger NPs (>50 nm) induce moderate increases in shoot/root length and chlorophyll content but exhibit less impact on enzymatic photosynthesis activity due to reduced cellular uptake. This size-dependent behavior highlights that smaller and medium-sized NPs better enhance photosynthesis through intracellular interaction and enzyme modulation, while larger sizes mainly exert indirect surface effects, with an overall need to optimize size to maximize photosynthesis benefits and minimize toxicity.

4.2. ROS generation and oxidative stress

Under environmental stress, plants inevitably produce ROS, such as superoxide anions (O₂˙⁻), hydroxyl radicals (˙OH), hydrogen peroxide (H₂O₂), and singlet oxygen (¹O₂).⁸⁹ Although moderate amounts of ROS possess signaling roles, overaccumulation halts cell processes and causes oxidative damage to membranes, proteins, RNA, and DNA, ultimately affecting the metabolism and causing cell death.^90–92 Reactive oxygen species overproduction is typically linked with photosynthetic dysfunction, especially in chloroplasts, where degradation of photosystem I (PSI) and II due to stress inhibits electron flow and enhances ROS production.^93,94 While plants have antioxidant defense systems that scavenge oxidative stress, these defenses are saturable in extreme or extended stress conditions.^95,96

The incorporation of NPs into agroecosystems introduces yet another layer to this redox imbalance. Their ability to cause or enhance oxidative stress is extremely particle size-sensitive. Nanoparticles, with their greater surface area-to-volume ratio and reactivity, are more likely to produce higher levels of ROS, adding to the oxidative load in plant cells. Fig. 1 shows the size-dependent impact of NPs on ROS metabolism in plants. Zinc oxide nanoparticles of the size range 5–50 nm greatly promoted malondialdehyde (MDA) content in plant roots with the highest lipid peroxidation.⁸⁵ Yusefi-Tanha et al. (2024) prepared CuO NPs in three sizes, 25 nm, 50 nm (medium), and 250 nm (large), all with identical surface charge, and compared their activities against dissolved Cu²⁺ ions (CuCl₂) and water controls.⁸⁰ By determining particle size effects while keeping surface charge constant, the study strengthened the argument for size-dependent toxicity. The results illustrated particle size-dependent activities, and the nCuO treatments efficiently induced remarkable increases in H₂O₂ and MDA contents of soybean leaves compared to the control. The strongest H₂O₂ and MDA values were initiated by the 25 nm nCuO, and the weakest by the 250 nm particles. In another study, 10 nm Fe₃O₄ NPs induced stronger oxidative stress in Hordeum vulgare L. (barley) root as compared to their 100 nm counterparts, again indicating the persistent trend in different nanomaterials.¹⁶

Fig. 1 Size-dependent impact of nanoparticles on ROS metabolism in plants. Nanoparticles of varying sizes enter plant cells and modulate ROS generation and detoxification. The left panel shows NADPH oxidase-driven ROS production at the membrane and subsequent scavenging by SOD, CAT, and POD. The right panel illustrates compartment-specific ROS metabolism in the cytosol, mitochondria, chloroplast, and peroxisome, highlighting antioxidant enzyme activities (SOD, APX, CAT, POD). Smaller NPs penetrate cells more efficiently and are more functional but may disrupt ROS balance; larger NPs are safer but less effective.

Apart from size, concentration and shape also affect NP-induced oxidative stress. Spherical Ag NP morphology (8 ± 2 nm) showed greater root growth inhibition in Arabidopsis thaliana L. (Arabidopsis) compared to triangular (47 ± 7 nm) or decahedral Ag NPs (45 ± 5 nm), showing the contribution of NP geometry as well as their size.⁹⁷ Similarly, Ag NPs of size 8 ± 2 nm inhibited root growth in Arabidopsis more severely than triangular (47 ± 7 nm) or decahedral Ag NPs (45 ± 5 nm), highlighting the relevance of NP geometry along with size.⁹⁷ In addition, surface chemistry is also conducive to this effect; hydrophilic 20 nm ZnO NPs were more prone to triggering lipid peroxidation than their larger or stearic acid-amended counterparts.⁹⁸ These results indicate the synergistic function of size and surface features in determining NP-induced oxidative reactions. Interestingly, not all small NPs trigger deleterious action. Even they can promote stress resistance at times. Selenium nanoparticles (10 nm), for instance, were found to reduce the level of H₂O₂ and MDA in pomegranate trees treated with salinity stress better than 50 nm selenium (Se) particles, which indicates an antioxidant function.¹⁴ It is in agreement with the sophisticated interaction among NP size, composition, and plant stress physiology, where less is not always more toxic.

In general, very small and small NPs (<20 nm) have high surface-area-to-volume ratios, leading to higher ROS generation due to more reactive sites. They can induce oxidative stress by causing lipid peroxidation and membrane damage if concentrations are excessive. However, some small NPs like Se NPs (10 nm) exhibit nanozyme activity that scavenges ROS, improve antioxidant defense and mitigating oxidative damage. Medium-sized NPs (20–50 nm) often balance ROS production and scavenging. Large NPs (>50 nm) generally cause less intracellular ROS generation due to limited cellular uptake but can cause mechanical damage at the cell surface or block nutrient transport, indirectly increasing oxidative stress. In summary, smaller NPs tend to induce higher ROS but can also boost antioxidant defenses depending on composition and dose; medium sizes typically provide antioxidative benefits with reduced toxicity, while larger particles mostly affect oxidative stress indirectly. Optimizing NP size is vital to balance ROS regulation for promoting plant health.

4.3. Antioxidant defense system

Plant antioxidant defense systems are responsible for the maintenance of redox balance and cell protection against oxidative stress caused by environmental stimuli and extrinsic agents, including NPs. Of the most important characteristics of NPs, particle size is especially significant in understanding how the particles will act on plant tissues and the capacity to cause oxidative stress. Smaller NPs with their higher surface area and reactivity generate more ROS, leading to cellular homeostasis disruption and activation of the plant antioxidant machinery. The defense mechanism has enzymatic components like superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) and non-enzymatic antioxidants like phenolics and flavonoids. The efficacy and potency of such an antioxidant response are largely dependent on NP size, influencing the level of oxidative stress as well as the ability of the plant to defend itself. It is thus pertinent to understand these size-dependent interactions in order to be able to avoid the phytotoxic risks of NPs and design the safe and effective agricultural application of NPs.

Li et al. (2023b) investigated the impact of ZnO NPs of different sizes (5, 20, and 50 nm) on rice. At a concentration of 25 mg L⁻¹, the smaller ZnO NPs (5 and 20 nm) notably increased SOD activity by 28.9% and 21.2%, and POD activity by 43.8% and 34.4%, respectively, compared to the control. Conversely, CAT activity was stimulated in the beginning but inhibited at Zn levels greater than 25 mg L⁻¹ with a drastic decline (p < 0.05).⁸⁵ Similarly, Wang et al. (2025) examined the influence of ZnO NPs of varying sizes (0, 30, 50, and 90 nm) on bentgrass under soil drenching. Leaf enzyme activities of SOD, POD, and CAT exhibited a pattern of first increasing and then decreasing with increasing ZnO nanoparticle size, reaching their peak values of 155.6, 2460.9, and 132.2 U g⁻¹ FW, respectively, at 50 nm.⁸⁴ These results show that an optimum ZnO NP size has a positive impact on leaf antioxidant enzyme activity. In another study, Fe₃O₄ NPs with median diameters of 10 nm (NP10) and 100 nm (NP100) introduced to barley in the germination and seedling phases showed size-dependent reduction of root CAT activity in NP10-treated roots in which enzyme activity reduced from 4.1 U mL⁻¹ in control roots to 2.46 U mL⁻¹ at 200 mg L⁻¹ NP10 treatment.¹⁶ NP100 exhibited no size-dependent reduction of CAT activity in leaf and root tissues at any concentration.

Recent studies also ascertain the function of smaller-sized NPs in the activation of antioxidant enzyme activity. For instance, foliation of plants with 10 nm Se NPs led to substantial enhancement of CAT, ascorbate peroxidase (APX), SOD, and POD activities in control as well as stress conditions. Importantly, Se NPs (10 nm) increased CAT activity by 18% in control and 26% in stress conditions, while other enzymes were also in the same direction.¹⁶ Conversely, 50 nm Se NPs showed lesser elevations in the activities of antioxidant enzymes, suggesting size as a major factor in the enhancement of plant resistance against oxidative stress. Likewise, in Arabidopsis seedlings, decahedral Ag NPs (45 ± 5 nm) and spherical (8 ± 2 nm) Ag NPs resulted in the minimum and maximum accumulation of Cu/Zn SOD (CSD2), respectively.⁹⁷ Yusef-Tanha et al. (2024b) established that antioxidative enzyme activities of SOD, CAT, peroxidase (POX), and APX were significantly affected by nCuO particle size. Among the treatments, nCuO-25 nm (small) caused maximum enzyme levels, reflecting a significant antioxidative response to balance increased oxidative stress.⁸⁰ Conversely, nCuO-250 nm (large) caused enzyme levels close to the control, reflecting minimal induction of stress. The intermediate nCuO-50 nm treatment revealed intermediate activities of antioxidant enzymes. Likewise, Cu²⁺ ion treatment also increased SOD, CAT, POX, and APX to a significant level, albeit in lower magnitudes than those induced by nCuO-25 nm but higher than the respective responses to large nCuO particles. The results demonstrate a definite particle size-dependent trend for the activation of antioxidant enzymes.

Under stress conditions also, the particle size of NPs plays crucial roles in the regulation of antioxidant defense, where smaller Se NPs (10 nm) induced much greater activity of antioxidant enzymes than larger particles (50 nm). Zahedi et al. (2021) reported that antioxidant enzyme activities in pomegranate plants were greatly boosted by Se NP foliar application, where greater effects were achieved using 10 nm particles than those of 50 nm. Under controlled/severe drought stress, 10 nm Se NP treatment increased CAT activities by 18/26%, APX by 33/19%, SOD by 38/12%, and POD by 18/16%. To compare, 50 nm Se NPs increased CAT by 7.2/10.1%, APX by 9.7/8.7%, SOD by 18.2/5.1%, and POD by 10.2/9.9%.¹⁴ The most active enzymes were always determined under extreme drought stress with the treatment of 10 nm Se NPs, revealing a strong size-sensitive antioxidant defense against drought stress.

Other non-enzymatic antioxidants like phenolic compounds and flavonoids are also part of the plant defense system. Miliauskienė et al. (2022) studied the size-dependent toxicity of ZnO NPs on foliar spray-treated Beta vulgaris ssp. cicla L. (Swiss chard) and found maximum flavonol index and total phenolic content (TPC) in the 35–45 nm ZnO NP-treated plants.⁹⁹ However, smaller (18 nm) and larger (80–200 nm) ZnO NPs were inhibitory to phenolic compounds, with the largest particles (80–200 nm) causing maximum inhibition of the non-enzymatic antioxidants. Surprisingly, antioxidant activity determined by using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS), and ferric reducing antioxidant power (FRAP) scavenging assays had no significant change for the 35–45 nm ZnO NPs but increased antioxidant activity with the 18 nm and 80–200 nm particles. This means that small NPs could potentially activate both enzymatic and non-enzymatic antioxidant defense systems more effectively, a thing that can be of great value under certain stress conditions.

Kang et al. (2024) showed that ZnO NPs not only affected enzymatic antioxidants but also significantly affected non-enzymatic antioxidant pathways in Vigna radiata L. (mung bean) sprouts.⁹⁸ Among treatments, pristine hydrophilic ZnO NPs (n-ZnO, 20 nm) caused maximum induction of secondary metabolite pathways, i.e., those related to flavonoid, flavone, flavonol, and isoflavonoid biosynthesis. These compounds are important non-enzymatic antioxidants and perform major stress defense and symbiotic nitrogen fixation functions. Enrichment factors of isoflavonoid biosynthesis were greater with n-ZnO treatment (0.12) than with stearic acid-modified hydrophobic ZnO (s-ZnO, 0.08), which reflects greater activation of protective metabolic processes. Unexpectedly, naringenin, a key intermediate in flavonoid and isoflavonoid metabolism, retained constant levels, indicating its regulatory function in attaining physiological harmony under stress. The elevated metabolic activation under n-ZnO exposure indicates its greater phytotoxicity and the plant's greater non-enzymatic antioxidant activity to counteract oxidative damage. Selenium nanoparticle foliar spray also markedly increased phenolic compounds in pomegranate under drought stress.¹⁴ The impact was greater with 10 nm than with 50 nm Se NPs. Specifically, 10 nm Se NP treatment demonstrated enhanced accumulation of TPC, α-punicalagin, β-punicalagin, and ellagic acid under control and drought stress. These results indicate that smaller Se NPs cause phenolic biosynthesis more intensely, leading to higher stress tolerance.

Small NPs (<20 nm) enhance antioxidant enzyme activities such as SOD, CAT, and APX, and non-enzymatic antioxidant content, helping reduce oxidative stress by scavenging ROS. They boost enzyme activities and non-enzymatic antioxidants to improve stress tolerance. Medium-sized NPs (20–50 nm) effectively increase antioxidant-related enzymes and metabolites (phenolics and proline), leading to strengthened redox homeostasis and enhanced plant growth under stress conditions. Large NPs (>50 nm) have limited uptake; they can indirectly stimulate antioxidant defenses by modifying the root or leaf microenvironment, contributing to moderate increases in antioxidant enzyme activities. Overall, NPs in the small to medium size range most efficiently fortify the antioxidant defense system by increasing enzymatic and non-enzymatic antioxidants, thus improving plant resilience against oxidative stress. This underlines the importance of nanoparticle size optimization for maximizing antioxidant benefits in plants.

4.4. Nutrient contents

Nanoparticles are found to have the promise of affecting plant translocation and uptake of nutrient components. The size of NPs plays a crucial role in influencing micronutrient levels because it directly affects their surface area, chemical reactivity, and the ability to be absorbed by plant roots. Various studies have investigated the influence of various sizes of NPs, including Fe₃O₄, Se, CuO, ZnO, and Fe₂O₃, on the elemental composition in various plant species, revealing the complex interactions between NPs and plant nutrition.

Smaller NPs, in general, increase the nutrient uptake with increased levels of the key elements in plant tissues. In soybean, for example, smaller CuO NPs (20 nm) favored nitrogen uptake and growth with increased nitrate levels and reduced ammonium, affecting nitrogen metabolism.¹⁰⁰ The size of CuO NPs also regulated the uptake and allocation of different elements in Phaseolus vulgaris L. (common bean) plants. 50 nm CuO NPs boosted enhanced nitrogen uptake and biomass productivity and assisted in trace element assimilation of nickel (Ni) and cobalt (Co).⁷⁰ This further reinforces the consideration that particle size not just determines primary nutrient assimilation but also affects trace element uptake.

Larger NPs may be less effective during nutrient translocation owing to the low capacity for plant tissue penetration. Zinc oxide nanoparticles (5, 20, and 50 nm) in rice root indicated that particle size of 5 nm exhibited the optimal Zn accumulation, additional proof to indicate the role of size of NPs in regulating nutrient uptake.⁸⁵ Equivalently, 10 nm Se NPs increased the intake of vital nutrients like potassium (K), calcium (Ca), magnesium (Mg), and phosphorus (P) in pomegranate plants, especially under stress conditions, indicating higher nutrient uptake with reduced sizes of NPs.¹⁴ Nutrient uptake is generally increased by smaller NPs, but even larger NPs can be beneficial, although the outcome depends on the plant type and conditions. For instance, in a study by Zahedi et al. (2021),¹⁴ 50 nm Se NPs also affected the assimilation of K, Ca, Mg, and P positively but to a lesser degree compared to that of particles of 10 nm. However, in some studies, there were findings showing that larger particles provided Cu content greater than when using minute particles.¹⁴

Magnetic iron oxide nanoparticle experiments also showed that larger particle sizes (100 nm) caused greater Cu accumulation compared to smaller particle sizes (10 nm), further illustrating the intricate relationship between NP size, concentration, and nutrient uptake.¹⁶ Al-Amri et al. (2020) determined that 20–40 nm Fe₂O₃ NPs supported higher iron (Fe) translocation to leaves compared to larger particle sizes (30–50 nm), proving medium-sized particles are superior in activating the mobility of nutrients in plants. Zinc oxide nanoparticles of different sizes (18 nm, 35–45 nm, and 80–200 nm) have yielded extensive effects on the elemental composition of Swiss chard leaves.⁸⁷ Smaller NPs caused enhanced Zn and Fe accumulation, whereas small particles (18 nm) triggered Zn accumulation.⁹⁹ 35–45 nm ZnO NP treatment also enhanced manganese concentration in Swiss chard and decreased boron (B) concentration, demonstrating the ability of NP size to influence the uptake and distribution of various nutrients simultaneously.

In short, the particle size of NPs significantly affects plant micronutrient content, affecting uptake, translocation, and trace element distribution such as Fe, Cu, K, Ca, and P. Smaller particles favor increased nutrient uptake and translocation, primarily under stress conditions, although the most favorable particle size depends on the nutrient and plant in question. Besides, the dose of NPs has implications for micronutrient uptake, and this has a complex interaction of particle size, dose, and response of the plant. These observations suggest the importance of serious consideration of NP size and dose in crop management for optimal plant nutrition and growth with minimal risk implications related to the use of NPs.

Cucumber plants were developed to maturity in soil with soil suspension of CeO₂ or ZnO NPs (10 ± 1 nm and 8 ± 1 nm) with concentrations of 0, 400, and 800 mg kg⁻¹. ICP-MS analysis indicated that the high-concentration treatments led to bioaccumulation of cerium (Ce) and Zn in the fruit (1.27 mg of Ce and 110 mg of Zn kg⁻¹ dry weight). In the present study, the Zn content in cucumber fruits at 400 and 800 mg kg⁻¹ ZnO NPs was 103 and 111 mg kg⁻¹ dry cucumber, while the control contained 46 mg Zn kg⁻¹ dry cucumber. However, ZnO NP-treated cucumber plants contain 2-fold Zn compared to the presently consumed cucumber.¹⁰¹

Nanoparticle size–element uptake interaction is plant- and nutrient-dependent and complex. Medium or larger NPs (like Fe₃O₄ or CuO NPs) in some studies have been found to facilitate greater accumulation of specific elements such as Cu or Fe than small NPs. Nanoparticle dose further interacts with size to manage uptake and translocation behavior, necessitating strategies of application in moderation. In general, NPs can enhance nutrient uptake by improving root absorption and altering rhizosphere microbial communities, which increase nutrient bioavailability and transport efficiency. Very small, small and medium sized NPs (<50 nm) show higher mobility and can penetrate roots and leaves more effectively, facilitating direct nutrient delivery and enhanced uptake. Nanoparticles act as slow-release carriers for fertilizers, improving nutrient stability and availability in the soil. This enhances sustained nutrient absorption by roots, reducing nutrient leaching and improving fertilizer use efficiency. Larger NPs (>50 nm) may have reduced penetration but influence nutrient uptake indirectly by modulating soil physicochemical properties and stimulating beneficial rhizosphere microbes that enhance nutrient cycling. The effect of NPs on nutrient uptake is dose-dependent; optimal concentrations promote plant growth and nutrient absorption, while excessive doses may inhibit both plant and microbial growth. In summary, NP size and dose critically regulate nutrient uptake by direct transport facilitation, slow nutrient release, and microbial community modulation, with particles below 50 nm generally showing the highest uptake efficiency.

4.5. Gene and proteomic responses

Plants, at the molecular level, adapt to stress through dynamically modified gene expression and their reprogrammed physiological processes.¹⁰² Stress cell gene products indirectly or directly support cells in defense against harm through induction of biosynthesis in the growth regulators, osmolytes, and antioxidants and augmentation of the activity and gene expression of detoxifying enzymes.¹⁰³ Importantly, the interaction of NPs with plant cells may confer effects on biological processes and gene expression, affecting plant development and growth.¹⁰⁴Fig. 2 depicts the size-dependent effects of NPs on plant gene expression and protein profiles. Arabidopsis was treated with Ag NPs of decahedral (45 ± 5 nm), triangular (47 ± 7 nm), and spherical (8 ± 2 nm) morphologies. Transcriptomics revealed upregulation of NCED3, IAA8, and RD22 as evidence of the stimulation of auxin (IAA)- and abscisic acid (ABA)-related stress signaling. Silver nanoparticles were also found to repress ACS7 and ACO2 expression, indicating repression of ethylene biosynthesis and signaling, releasing the inhibition of root growth caused by 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase. Nanoparticle size of 45 nm and 8 nm induced the lowest and highest root inhibition and Cu/Zn SOD accumulation. The three forms elicited protein accumulation related to pivotal biological processes such as CDC2 (cell division), POR (chloroplast development), and FBA (carbohydrate metabolism). In general, Ag NPs regulated ROS levels and triggered sets of genes for proliferation, hormone signaling, and metabolism in a morphology-dependent manner. They show how Ag NP size and shape are important determinants of their physiological and molecular activities in plants.⁹⁷

Fig. 2 Size-dependent effects of nanoparticles on plant gene expression and protein profiles. Nanoparticles of different sizes induce transcriptional reprogramming, leading to gene upregulation or downregulation. Nanoparticle size influences the expression of stress-related genes (IAA8, NCED3, RD22), ion channel proteins, and proteins involved in cell division, photosynthesis, metabolism, and stress response. Smaller and larger NPs elicit distinct molecular responses, highlighting their differential regulatory effects on plant physiology.

Nanoparticle size also influences protein content in plants. Prasad et al. (2017) reported size-dependent effects of phytogenic Ag NPs, synthesized using candyleaf leaf extract, on seed germination, growth, and biochemical parameters of rice, maize, and peanut. Silver nanoparticles of varying sizes (S1–77.5 nm, S2–111.7 nm, S3–68.6 nm, S4–98.9 nm) showed significant size-dependent changes in leaf protein content. In rice, protein content increased by up to 251% (S3); in maize, by 433% (S3); and in peanuts, by 74% (S1), compared to controls.⁸⁸ Bulk Ag treatments generally led to a decrease in protein content. The study highlights the critical role of NP size in enhancing crop biochemical responses. A comparative proteomics investigation identified that the molecular response of soybean seedlings during flooding stress was significantly influenced by the size of Ag NPs. Treatment with 2, 15, and 50–80 nm Ag NPs led to differential protein abundance changes, and 228 proteins significantly varied. 15-nm Ag NPs had the most significant positive impact among them. They induced the production of proteins with amino acid metabolic and ribosomal protein activities while decreasing general protein synthesis protein levels, which is a redistribution of cellular resources under stress conditions. In contrast, neither 50–80 nm nor 2 nm-sized Ag NPs induced the same positive responses. Upregulation of ribosomal proteins under 15 nm Ag NP exposure indicates enhanced protein synthesis machinery, supporting growth and stress acclimation. Conversely, the decreased enzymatic activity of beta-ketoacyl reductase despite its gene being upregulated suggests complex post-transcriptional or feedback mechanisms controlling metabolic pathways. These protein-level changes align physiologically with improved root and hypocotyl growth and increased expression of amino acid and wax biosynthesis proteins, which are crucial for flooding stress tolerance.¹⁰⁵

Proteomic investigation revealed that aluminum oxide nanoparticles (Al₂O₃ NPs) cause size-dependent molecular reactions in flood-stressed soybeans. Various particle sizes, 5 nm, 30–60 nm, and 135 nm, induced protein expression and process changes. Aluminum oxide nanoparticles sized 30–60 nm induced root and hypocotyl elongation and enhanced stress acclimation. At the molecular level, this size limited glycolysis-associated proteins and turned on the ascorbate–glutathione antioxidant pathway, increasing the ROS scavenging activity of the plant. Ribosomal proteins were also increased, reflecting stimulated protein synthesis on mid-sized NP exposure. However, 135 nm Al₂O₃ NPs affected mitochondrial function predominantly. The proteomic analysis showed increased voltage-dependent anion channel proteins, reflecting changed mitochondrial membrane permeability in large NP treatment. Concurrently, treatment with 5 nm Al₂O₃ NPs resulted in the overexpression of isocitrate dehydrogenase, an important enzyme of the tricarboxylic acid (TCA) cycle, suggesting increased mitochondrial metabolic activity. In summary, the above data demonstrate that Al₂O₃ NPs trigger size-dependent responses in soybean plants subjected to flooding stress by regulating root growth, antioxidant defense, protein synthesis, and mitochondrial activity in a size-dependent manner.¹⁰⁶

In summary, NP size critically facilitates efficient cellular uptake and interaction with genetic material, impacting gene expression and protein profiles linked to stress responses and plant development. Smaller NPs tend to be more effective in these molecular interactions but also pose risks of genotoxicity if not optimized.

5. Size-based impacts of NPs on plant-associated microbes

The impact of NPs on plant–microbe interactions remains a critical concern. The size of NPs plays a pivotal role in determining their behavior in the rhizosphere. Wang et al. (2025) explored the size-dependent effects of ZnO NPs (30, 50, and 90 nm) on bentgrass, focusing on physiological responses, root exudation patterns, and rhizospheric microbial communities.⁸⁴ Root exudate analysis revealed enhanced secretion of organic compounds at 30 and 50 nm, suggesting improved root activity and plant–microbe signaling, whereas 90 nm NPs suppressed this response. 16S rRNA gene sequencing showed that microbial diversity peaked at 50 nm, while larger particles (90 nm) reduced the abundance of beneficial microbes such as Bryobacter and Methylophilus. Similarly, Przemieniecki et al. (2024) also revealed size-dependent effects of TiO₂ NPs on the structure and function of wheat rhizobiome. While large TiO₂ NPs (>100 nm) and small TiO₂ disrupted microbial communities and favored autotrophs, medium-sized TiO₂ NPs (68 nm) enriched chemoheterotrophic microbes, including beneficial plant growth-promoting bacteria (PGPB) and fungal saprotrophs.¹⁰⁷ In contrast, smaller forms led to less diverse, oligotrophic conditions and reduced plant–microbe associations. These findings emphasize the critical role of particle size in shaping rhizosphere dynamics and inform safer, more effective nanomaterial use in agriculture. In another study, the application of various types of Ag NPs had differential but generally moderate effects on soil bacterial community abundance and composition. Silver nanoparticles with smaller size and positive charge enhanced harmful microbiota, whereas Ag NPs with bigger size enhanced the abundance of bacteria associated with plant growth-promoting traits, such as the production of phytohormones, hydrogen sulfide (H₂S), proteases, siderophores, and phosphatases as well as autotrophic and nitrogen-fixing capabilities.¹⁰⁷

The enhanced root exudation and increased microbial diversity observed at certain NP sizes suggest an underlying relationship, where smaller or medium-sized NPs stimulate root metabolic activity that directly promotes the secretion of organic compounds. These exudates serve as substrates and signaling molecules that shape rhizospheric microbial communities, leading to a higher abundance of beneficial microbes and improved plant–microbe interactions. Conversely, larger NPs may suppress root exudation and reduce microbial diversity, highlighting the size-dependent modulation of rhizosphere dynamics by NPs. This evidence collectively supports that NP size influences root exudation patterns and microbial community composition, with significant implications for plant health and soil ecosystems.

6. Size-dependent growth and nanotoxicity in plants

The size of NPs also defines their ability to impact plant structures, for example, entering the cells of a plant, distributing themselves over the cells, and even causing damage to the plant. Larger NPs have phytotoxicity due to the sticking of particles on the leaf epidermal cell walls more frequently and less penetrating ability into the plants compared to smaller NPs. This enables them to interact with various cellular structures, typically inflicting severe damage. It has been demonstrated that smaller NPs tend to produce extreme ultrastructural alterations, like burst cell walls, distorted mitochondria, and disordered chloroplasts, which could have adverse effects on the physiological activities of the plant, including photosynthesis. The increased reactivity of smaller NPs has the potential to lead to the production of ROS that then cause significant cellular constituent damage, like lipids, proteins, and DNA. For example, Li et al. (2023b) reported that small ZnO NPs (5–50 nm) caused severe damage to rice leaf cell structure, but large ZnO particles (100 nm) had very negligible effects, indicating a strong relationship between particle size and NP toxicity. Likewise, Yusef-Tanha et al. (2024) indicated that small CuO NPs (25 nm) disturbed cell wall structure and plasma membranes, causing defective nutrient storage and oil content in soybean plants.^80,85 In contrast, larger NPs (250 nm) are less toxic to plant cells because of their decreased capacity to penetrate tissues. These larger particles will remain on the surface of plant cells instead of entering them, thereby reducing their exposure to essential cellular components. For example, Leopold et al. (2022) reported that TiO₂ NPs (100 nm) were not responsible for any ultrastructural injury to soybean leaves or roots, indicating that larger NPs have fewer chances of disrupting cellular integrity.¹⁰⁸ Furthermore, large NPs will generate fewer ROS and perhaps not initiate the same extent of oxidative stress or protective response as small NPs, again to their advantage in terms of lowered toxicity.

One of the most vital factors influencing the impact of NPs on plant cell components is their tendency for agglomeration, or clumping, particularly at higher concentrations. The bigger the size of NPs, the greater the possibility of agglomeration, which would deter their ability to penetrate into plant cells effectively. For instance, Tombuloglu et al. (2024b) proved that 100 nm Fe₃O₄ NPs induced less cellular damage than smaller NPs of 10 nm, possibly because of agglomeration, which lowered the plant cell uptake efficiency.¹⁶ This is the effect of agglomeration, proving how complex the behavior of NPs is in plants because it can change their bioavailability and lower their toxicity risk. Untreated hydrophilic n-ZnO NPs with smaller size (20 nm) and bigger size (100 nm) and stearic acid-coated hydrophobic ZnO NPs of 20 nm were used in mung bean sprouts and established that the small-sized n-ZnO NPs inhibited root growth more significantly than the big-sized b-ZnO, slowing root growth by 37.14 and 16.96%, respectively.⁹⁸ In the case of Ag NPs, the toxicity was less dependent on size but present, nonetheless. 20–40 nm and 80–100 nm Ag NPs did not inhibit growth significantly at up to 200 mg L⁻¹ levels while retaining more than 71% of control activity on rice.¹⁰⁹ At lower concentration levels (up to 20 mg L⁻¹), smaller Ag NPs completely inhibited root growth. These NPs were more toxic, reflecting their EC₅₀ values (10 mg L⁻¹ for 20–40 nm NPs versus 13.4 mg L⁻¹ for 80–100 nm NPs). This is reflective of the bivalent nature of NP size: while small particles are better penetrators of tissues and vehicles of delivery of active ingredients, they also pose a higher risk of toxicity since they are more reactive and have close contact with the plant cells. To elucidate nanotoxicity in plants, Li et al. (2023b) characterized in vivo distribution of ZnO NPs of various sizes (5, 20, and 50 nm) in rice.⁸⁵ The small ZnO NPs suppressed root growth and biomass, induced membrane damage, enhanced MDA content, and stimulated antioxidant enzymes. In rice, much higher releases of Zn²⁺ ions from the smaller ZnO NP size (5 nm) were observed in comparison with the larger sizes (20 nm and 50 nm). After 72 hours, 5 nm NPs released 9.26 mg L⁻¹ Zn²⁺ at 100 mg L⁻¹. However, the same concentration of zinc sulfate (ZnSO₄) in Hoagland's solution, which directly provides Zn²⁺ ions, showed no inhibition of growth. This suggests that nanotoxicity is not simply a matter of the release of ions but also physical and mechanical contact between root plants and NPs. Smaller NPs with a high surface area-to-volume ratio would readily access plant cells with potential nanomechanical damage to root structure. Laser ablation of ICP-OES and TEM analysis had proof for the accumulation and uptake of ZnO NPs in rice root tissue. The evidence indicates ZnO NP-induced size-dependent phytotoxicity.

The size-dependent activity of NPs was also reported by Li et al. (2023a), who discovered root volume inhibition to be higher by smaller ZnO NPs (5 nm) than by larger particles (50 nm), although the latter induced higher root diameter.¹¹⁰ This is due to smaller NPs having higher reactivity and surface area, being more bioavailable and having stronger interaction with plant tissues. On the other hand, medium-diameter ZnO NPs (35–45 nm) were detected to be most effective in inducing biomass production in Swiss chard, indicating an optimal size range to induce plant growth.⁹⁹ Kim et al. (2024) have explored that ZnO NPs (30 nm) can increase plant stress tolerance, especially in salinity and drought stresses, through enhanced root biomass and overall stress tolerance.⁷⁹ Conversely, smaller NPs, such as Au NPs (10 nm), were more phytotoxic to Arabidopsis than their larger counterparts (14–18 nm), thereby suggesting the danger of small NPs, particularly when used in higher doses. Lead dioxide (PbO₂) (10 ± 3 nm) and lead oxide (PbO) (20 ± 5 nm) NPs showed size-dependent toxicity in maize, with smaller PbO₂ NPs causing greater effects. These NPs disrupted seed germination, root growth, nutrient uptake, and biomass production by accumulating in plant tissues via water uptake and transport pathways, posing risks to food security and human health.⁸⁵ Sarkar et al. (2025) investigated the effects of Si NPs of three different sizes (30, 50, and 100 nm) and found that 50 nm Si NPs were relatively less toxic, both in Allium cepa L. (onion) root cells and Vicia lens L. (lentil) plants.¹¹¹ In onion, 50 nm Si NPs exhibited a higher mitotic index (MI) and lower chromosomal aberrations (CAs) at lower doses (50–100 g L⁻¹) compared to smaller (30 nm) and larger (100 nm) particles.

In general, the size of NPs is a major factor in determining how they interact with plant cells and the extent to which they can damage cells. Small NPs, by virtue of greater cellular uptake and greater surface area, are more toxic and can cause severe ultrastructural cell damage to plants. Large NPs are less disruptive since they are less prone to enter plant cells and cause intracellular damage. The affinity of small NPs to agglomerate hinders their effect on cell structures and may restrict their capacity to penetrate plant tissues. These findings emphasize the importance of taking additional precautions while using NP size in studying the potential effects in agricultural uses. By managing the properties of NPs, it is feasible to reduce toxicity and enhance NPs' benefits in triggering plant growth and strength.

7. Challenges, conclusion, and future directions

The integration of engineered NPs into agricultural practices offers considerable potential for enhancing crop yields and nutrient use efficiency. However, their widespread application raises concerns regarding potential risks to plant systems and the environment. Among the factors influencing NP–plant interactions, particle size is a critical determinant of both efficacy and toxicity. Nanoparticle size critically influences their interactions with plants, affecting physiological, molecular, and ecological processes. Small NPs (<20 nm) can penetrate plant cellular barriers more easily and exhibit high surface reactivity, enhancing photosynthesis and antioxidant enzyme activities but also increasing risks of oxidative stress and toxicity when overaccumulated. Medium-sized NPs (20–50 nm) strike a balance by promoting chlorophyll synthesis, nutrient uptake, and antioxidant defenses with lower toxicity, supporting improved growth and stress resilience. Larger NPs (>50 nm), although less mobile and bioavailable, influence plant growth primarily through surface interactions and modulation of soil and microbial environments, which indirectly affect plant health. Regarding oxidative stress, smaller NPs tend to generate higher ROS, eliciting both damaging and signaling responses that modulate antioxidant systems such as SOD and CAT enzymes. Gene and proteomic profiles respond dynamically to nanoparticle exposure, especially with smaller sizes facilitating intracellular interactions and altered expression of stress-related proteins. Plant-associated microbial communities are similarly impacted in a size-dependent manner; smaller particles exhibit potent antimicrobial effects against pathogens but may also harm beneficial microbes, whereas medium and larger NPs tend to foster beneficial microbial activity, supporting nutrient cycling and plant growth. Toxicity remains a significant concern, with smaller and highly reactive NPs more prone to cause cellular damage, inhibit growth, and induce genotoxic effects, depending on concentration, coating, and plant species. This highlights the imperative of optimizing nanoparticle size and physicochemical properties to maximize agricultural benefits while minimizing adverse effects.

Future research must address several key gaps. Long-term field studies under realistic agricultural conditions are needed to evaluate cumulative effects, persistence in soil, and potential bioaccumulation.^112,113 Additionally, the interplay between NP properties and environmental factors such as soil pH, moisture, and microbial activity remains insufficiently understood.¹¹³ The mechanistic relationship between NP size regulation through various methods and their uptake, translocation and accumulation pathways in plants should be clarified. Particular attention should be given to how the size uniformity of chemically synthesized NPs affects root penetration efficiency compared with biologically derived NPs. Regulatory frameworks should evolve to incorporate not only particle size but also aggregation tendencies, surface functionalization, and bioaccumulation risks.^113,114 A comprehensive understanding of NP behavior across diverse crop species and developmental stages will be essential for establishing safe application thresholds.¹¹²

In conclusion, while NPs hold promise for transforming agricultural productivity, their safe and sustainable integration will depend on targeted research, adaptive regulations, and evidence-based application strategies. Continued investigation into size-dependent dynamics will equip researchers and policymakers with the knowledge necessary to maximize benefits while minimizing risks, paving the way for resilient and productive agroecosystems.

Author contributions

SS and KMS: conceptualization, writing of original draft, critical review and editing. RSD and ABJ: critical review of the manuscript. PS: conceptualization, supervision, writing of original draft, critical review and editing. All authors read, commented, and approved the manuscript.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

Data sharing is not applicable to this article as no datasets were generated or analysed during the current study.

Acknowledgements

The authors extend their gratitude to the Central University of Gujarat, Gandhinagar, India, for providing the necessary facilities. KMS and SS are thankful to UGC for the non-NET fellowship.

References

1. S. Bashir, N. H. A. Kadir, Y. A. M. Naji and S. Ramesh, Commercialization and Market Potential of Nanobiostimulants, in Nanobiostimulants: Emerging Strategies for Agricultural Sustainability, Springer Nature Switzerland, Cham, 2024, pp. 399–417,  DOI:10.1007/978-3-031-68138-7_17.
2. K. M. Singh, S. Baksi, S. Rani, A. B. Jha, R. S. Dubey and P. Sharma, NanoBoost: Maximizing crop resilience and yield via nanopriming under salt stress, Environ. Exp. Bot., 2024, 105937,  DOI:10.1016/j.envexpbot.2024.105937.
3. S. Soni, A. B. Jha, R. S. Dubey and P. Sharma, Mitigating cadmium accumulation and toxicity in plants: The promising role of nanoparticles, Sci. Total Environ., 2024, 912, 168826,  DOI:10.1016/j.scitotenv.2023.168826.
4. S. Soni, A. B. Jha, R. S. Dubey and P. Sharma, Nanowonders in agriculture: Unveiling the potential of nanoparticles to boost crop resilience to salinity stress, Sci. Total Environ., 2024, 925, 171433,  DOI:10.1016/j.scitotenv.2024.171433.
5. C. Deng, Y. Wang, G. Navarro, Y. Sun, K. Cota-Ruiz, J. A. Hernandez-Viezcas and J. Gardea-Torresdey, Copper oxide (CuO) nanoparticles affect yield, nutritional quality, and auxin associated gene expression in weedy and cultivated rice (Oryza sativa L.) grains, Sci. Total Environ., 2022, 810, 152260,  DOI:10.1016/j.scitotenv.2021.152260.
6. A. Hazarika, M. Yadav, D. K. Yadav and H. S. Yadav, An overview of the role of nanoparticles in sustainable agriculture, Biocatal. Agric. Biotechnol., 2022, 43, 102399,  DOI:10.1016/j.bcab.2022.102399.
7. S. Tripathi, S. Mahra, K. Tiwari, S. Rana, D. K. Tripathi, S. Sharma and S. Sahi, Recent advances and perspectives of nanomaterials in agricultural management and associated environmental risk: a review, Nanomaterials, 2023, 13(10), 1604,  DOI:10.3390/nano13101604.
8. L. Tang, T. M. Fan, L. B. Borst and J. Cheng, Synthesis and biological response of size-specific, monodisperse drug-silica nanoconjugates, ACS Nano, 2012, 6(5), 3954–3966,  DOI:10.1021/nn300149c.
9. A. Avellan, J. Yun, Y. Zhang, E. Spielman-Sun, J. M. Unrine, J. Thieme and G. V. Lowry, Nanoparticle size and coating chemistry control foliar uptake pathways, translocation, and leaf-to-rhizosphere transport in wheat, ACS Nano, 2019, 13(5), 5291–5305,  DOI:10.1021/acsnano.8b09781.
10. L. S. B. L. Oliveira and K. D. Ristroph, Critical review: uptake and translocation of organic nanodelivery vehicles in plants, Environ. Sci. Technol., 2024, 58(13), 5646–5669,  DOI:10.1021/acs.est.3c09757.
11. C. M. Rico, S. Majumdar, M. Duarte-Gardea, J. R. Peralta-Videa and J. L. Gardea-Torresdey, Interaction of nanoparticles with edible plants and their possible implications in the food chain, J. Agric. Food Chem., 2011, 59(8), 3485–3498,  DOI:10.1021/jf104517j.
12. D. Lin and B. Xing, Phytotoxicity of nanoparticles: inhibition of seed germination and root growth, Environ. Pollut., 2007, 150(2), 243–250,  DOI:10.1016/j.envpol.2007.01.016.
13. Z. Li, W. Yan, Y. Li, Y. Xiao, Y. Shi, X. Zhang and G. Jiang, Particle size determines the phytotoxicity of ZnO nanoparticles in rice (Oryza sativa L.) revealed by spatial imaging techniques, Environ. Sci. Technol., 2023, 57(36), 13356–13365,  DOI:10.1021/acs.est.3c03821.
14. S. M. Zahedi, M. S. Hosseini, N. D. H. Meybodi and W. Peijnenburg, Mitigation of the effect of drought on growth and yield of pomegranates by foliar spraying of different sizes of selenium nanoparticles, J. Sci. Food Agric., 2021, 101(12), 5202–5213,  DOI:10.1002/jsfa.11167.
15. L. Yin, Y. Cheng, B. Espinasse, B. P. Colman, M. Auffan, M. Wiesner and E. S. Bernhardt, More than the ions: the effects of silver nanoparticles on Lolium multiflorum, Environ. Sci. Technol., 2011, 45(6), 2360–2367,  DOI:10.1021/es103995x.
16. G. Tombuloglu, A. Aldahnem, H. Tombuloglu, Y. Slimani, S. Akhtar, K. R. Hakeem and A. Manikandan, Uptake and bioaccumulation of iron oxide nanoparticles (Fe3O4) in barley (Hordeum vulgare L.): Effect of particle-size, Environ. Sci. Pollut. Res., 2024, 31(14), 22171–22186,  DOI:10.1007/s11356-024-32378-y.
17. D. Paramelle, A. Sadovoy, S. Gorelik, P. Free, J. Hobley and D. G. Fernig, A rapid method to estimate the concentration of citrate capped silver nanoparticles from UV-visible light spectra, Analyst, 2014, 139(19), 4855–4861,  10.1039/C4AN00978A.
18. H. N. Fernando, U. R. Kumarasinghe, C. P. Gunasekara, S. K. Wijekoon, A. K. Ekanayaka, S. P. Rajapaksha and P. M. Jayaweera, Synthesis, characterization and antimicrobial activity of garcinol capped silver nanoparticles, J. Microbiol. Biotechnol., 2019, 1841–1851,  DOI:10.4014/jmb.1904.04032.
19. A. Selmani, D. Kovačević and K. Bohinc, Nanoparticles: From synthesis to applications and beyond, Adv. Colloid Interface Sci., 2022, 303, 102640,  DOI:10.1016/j.cis.2022.102640.
20. S. Khan and M. K. Hossain, Classification and properties of nanoparticles, in Nanoparticle-based polymer composites, Woodhead Publishing, 2022, pp. 15–54,  DOI:10.1016/B978-0-12-824272-8.00009-9.
21. K. A. Altammar, A review on nanoparticles: characteristics, synthesis, applications, and challenges, Front. Microbiol., 2023, 14, 1155622,  DOI:10.3389/fmicb.2023.1155622.
22. N. V. K. Thanh, N. D. Giang, L. Q. Vinh and H. T. Dat, A low cost microwave synthesis method for preparation of gold nanoparticles, Commun. Phys., 2014, 24(2), 153–161,  DOI:10.15625/0868-3166/24/2/3809.
23. Q. Wu, L. Qiu, L. Zhang, H. Liu, R. Ma, P. Xie and M. He, Temperature-dependent selective nucleation of single-walled carbon nanotubes from stabilized catalyst nanoparticles, Chem. Eng. J., 2022, 431, 133487,  DOI:10.1016/j.cej.2021.133487.
24. R. Zhang, A. Khalizov, L. Wang, M. Hu and W. Xu, Nucleation and growth of nanoparticles in the atmosphere, Chem. Rev., 2012, 112(3), 1957–2011,  DOI:10.1021/cr2001756.
25. N. R. Jana, L. Gearheart and C. J. Murphy, Evidence for seed-mediated nucleation in the chemical reduction of gold salts to gold nanoparticles, Chem. Mater., 2001, 13(7), 2313–2322,  DOI:10.1021/cm000662n.
26. A. Kołodziejczak-Radzimska and T. Jesionowski, Zinc oxide-from synthesis to application: a review, Materials, 2014, 7(4), 2833–2881,  DOI:10.3390/ma7042833.
27. C. Nwabunwanne, S. O. Aisida, R. Javed, C. Awada, A. Alshoaibi and F. Ezema, Magnetic nanoparticles: biosynthesis, characterization, surface functionalization and biomedical applications, J. Indian Chem. Soc., 2025, 101617,  DOI:10.1016/j.jics.2025.101617.
28. A. Ulu, S. A. A. Noma, A. Kuruçay, S. D. Topel, M. Asiltürk and B. Ateş, Design of near-infrared light induced functionalized upconverting nanoparticles as support in enzyme immobilization: Enhanced biocatalyst activity and stability, Int. J. Biol. Macromol., 2025, 140581,  DOI:10.1016/j.ijbiomac.2025.140581.
29. Y. Y. Chan, Y. L. Pang, S. Lim and W. C. Chong, Facile green synthesis of ZnO nanoparticles using natural-based materials: Properties, mechanism, surface modification and application, J. Environ. Chem. Eng., 2021, 9(4), 105417,  DOI:10.1016/j.jece.2021.105417.
30. I. Toledo-Manuel, M. Pérez-Alvarez, G. Cadenas-Pliego, C. J. Cabello-Alvarado, A. S. Ledezma-Pérez, J. M. Mata-Padilla and C. N. Alvarado-Canché, Functionalization methods for ZnO nanoparticles with citric acid and their effect on antimicrobial activity, Ceram. Int., 2024, 50(21), 42195–42206,  DOI:10.1016/j.ceramint.2024.08.063.
31. S. M. Dizaj, F. Lotfipour, M. Barzegar-Jalali, M. H. Zarrintan and K. Adibkia, Antimicrobial activity of the metals and metal oxide nanoparticles, Mater. Sci. Eng., C, 2014, 44, 278–284,  DOI:10.1016/j.msec.2014.08.031.
32. E. O. Ogunsona, R. Muthuraj, E. Ojogbo, O. Valerio and T. H. Mekonnen, Engineered nanomaterials for antimicrobial applications: A review, Appl. Mater. Today, 2020, 18, 100473,  DOI:10.1016/j.apmt.2019.100473.
33. L. Liu, Y. Zhang, C. Li, J. Cao, E. He, X. Wu and L. Wang, Facile preparation PCL/modified nano ZnO organic-inorganic composite and its application in antibacterial materials, J. Polym. Res., 2020, 27, 1–11,  DOI:10.1007/s10965-020-02046-z.
34. K. Upadhyay, R. K. Tamrakar, S. Thomas and M. Kumar, Surface functionalized nanoparticles: a boon to biomedical science, Chem.-Biol. Interact., 2023, 380, 110537,  DOI:10.1016/j.cbi.2023.110537.
35. S. Salatin, S. Maleki Dizaj and A. Yari Khosroushahi, Effect of the surface modification, size, and shape on cellular uptake of nanoparticles, Cell Biol. Int., 2015, 39(8), 881–890,  DOI:10.1002/cbin.10459.
36. I. Manna and M. Bandyopadhyay, A review on the biotechnological aspects of utilizing engineered nanoparticles as delivery systems in plants, Plant Gene, 2019, 17, 100167,  DOI:10.1016/j.plgene.2018.100167.
37. O. Afshari and Z. Salehi, β-Cyclodextrin and APTES functionalized magnetic iron oxide nanoparticles for improved lipase immobilization, transesterification efficiency, and reusability, J. Ind. Eng. Chem., 2025, 144, 476–486,  DOI:10.1016/j.jiec.2024.09.043.
38. S. Liu, L. Zhu, W. Cao, P. Li, Z. Zhan, Z. Chen and J. Wang, Defect-related optical properties of Mg-doped ZnO nanoparticles synthesized via low temperature hydrothermal method, J. Alloys Compd., 2021, 858, 157654,  DOI:10.1016/j.jallcom.2020.157654.
39. L. R. Pokhrel, B. Dubey and P. R. Scheuerman, Impacts of select organic ligands on the colloidal stability, dissolution dynamics, and toxicity of silver nanoparticles, Environ. Sci. Technol., 2013, 47(22), 12877–12885.
40. A. Cartwright, K. Jackson, C. Morgan, A. Anderson and D. W. Britt, A review of metal and metal-oxide nanoparticle coating technologies to inhibit agglomeration and increase bioactivity for agricultural applications, Agronomy, 2020, 10(7), 1018.
41. G. Gohari, S. Panahirad, M. Sadeghi, A. Akbari, E. Zareei, S. M. Zahedi and V. Fotopoulos, Putrescine-functionalized carbon quantum dot (put-CQD) nanoparticles effectively prime grapevine (Vitis vinifera cv.'Sultana') against salt stress, BMC Plant Biol., 2021, 21, 1–15,  DOI:10.1186/s12870-021-02901-1.
42. S. F. Fatehi, M. Oraei, G. Gohari, A. Akbari and A. Faramarzi, Proline-functionalized graphene oxide nanoparticles (GO-Pro NPs) mitigate salt-induced adverse effects on morpho-physiological traits and essential oils constituents in Moldavian Balm (Dracocephalum moldavica L.), J. Plant Growth Regul., 2022, 41(7), 2818–2832,  DOI:10.1007/s00344-021-10477-1.
43. S. Hajihashemi and S. Kazemi, The potential of foliar application of nano-chitosan-encapsulated nano-silicon donor in amelioration the adverse effect of salinity in the wheat plant, BMC Plant Biol., 2022, 22(1), 148,  DOI:10.1186/s12870-022-03531-x.
44. S. Iravani, Green synthesis of metal nanoparticles using plants, Green Chem., 2011, 13(10), 2638–2650,  10.1039/c1gc15386b.
45. X. Ji, X. Song, J. Li, Y. Bai, W. Yang and X. Peng, Size control of gold nanocrystals in citrate reduction: the third role of citrate, J. Am. Chem. Soc., 2007, 129(45), 13939–13948,  DOI:10.1021/ja074447k.
46. A. P. LaGrow, B. Ingham, M. F. Toney and R. D. Tilley, Effect of surfactant concentration and aggregation on the growth kinetics of nickel nanoparticles, J. Phys. Chem. C, 2013, 117(32), 16709–16718,  DOI:10.1021/jp405314g.
47. S. F. Chin, S. C. Pang and S. H. Tay, Size controlled synthesis of starch nanoparticles by a simple nanoprecipitation method, Carbohydr. Polym., 2011, 86(4), 1817–1819,  DOI:10.1016/j.carbpol.2011.07.012.
48. E. Masoudipour, S. Kashanian, A. H. Azandaryani, K. Omidfar and E. Bazyar, Surfactant effects on the particle size, zeta potential, and stability of starch nanoparticles and their use in a pH-responsive manner, Cellulose, 2017, 24, 4217–4234,  DOI:10.1007/s10570-017-1426-3.
49. P. Malik, R. Shankar, V. Malik, N. Sharma and T. K. Mukherjee, Green chemistry based benign routes for nanoparticle synthesis, J. Nanopart., 2014, 2014(1), 302429,  DOI:10.1155/2014/302429.
50. J. K. Patra and K. H. Baek, Green nanobiotechnology: factors affecting synthesis and characterization techniques, J. Nanomater., 2014, 2014(1), 417305,  DOI:10.1155/2014/417305.
51. L. B. Anigol, J. S. Charantimath and P. M. Gurubasavaraj, Effect of concentration and pH on the size of silver nanoparticles synthesized by green chemistry, Organic & Medical Chemistry International Journal, 2017, 3(5), 1–5,  DOI:10.19080/OMCIJ.2017.03.555622.
52. D. V. Francis, T. Aiswarya and T. Gokhale, Optimization of the incubation parameters for biogenic synthesis of WO3 nanoparticles using Taguchi method, Heliyon, 2022, 8(9), e10640,  DOI:10.1016/j.heliyon.2022.e10640.
53. P. E. Antezana, S. Municoy and M. F. Desimone, Building nanomaterials with microbial factories, in Biogenic Sustainable Nanotechnology, Elsevier, 2022, pp. 1–39,  DOI:10.1016/B978-0-323-88535-5.00012-3.
54. R. Ravichandran, Nanotechnology applications in food and food processing: innovative green approaches, opportunities and uncertainties for global market, Int. J. Green Nanotechnol. Phys. Chem., 2010, 1(2), P72–P96,  DOI:10.1080/19430871003684440.
55. A. Nande, S. Raut, M. Michalska-Domanska and S. J. Dhoble, Green synthesis of nanomaterials using plant extract: a review, Curr. Pharm. Biotechnol., 2021, 22(13), 1794–1811,  DOI:10.2174/1389201021666201117121452.
56. V. V. Makarov, A. J. Love, O. V. Sinitsyna, S. S. Makarova, I. V. Yaminsky, M. E. Taliansky and N. O. Kalinina, “Green” nanotechnologies: synthesis of metal nanoparticles using plants, Acta Naturae, 2014, 6, 35–44,  DOI:10.32607/20758251-2014-6-1-35-44.
57. P. L. Santo-Orihuela, M. F. Desimone and P. N. Catalano, Green synthesis: a land of complex nanostructures, Curr. Pharm. Biotechnol., 2023, 24(1), 3–22,  DOI:10.2174/1389201023666220512094533.
58. L. Colleselli, M. Mutschlechner, M. Spruck, F. Albrecht, O. I. Strube, P. Vrabl and H. Schöbel, Light-mediated biosynthesis of size-tuned silver nanoparticles using Saccharomyces cerevisiae extract, Bioprocess Biosyst. Eng., 2024, 47(10), 1669–1682,  DOI:10.1007/s00449-024-03060-x.
59. S. A. Aromal and D. Philip, Green synthesis of gold nanoparticles using Trigonella foenum-graecum and its size-dependent catalytic activity, Spectrochim. Acta, Part A, 2012, 97, 1–5.
60. A. Balachandran, S. P. Sreenilayam, K. Madanan, S. Thomas and D. Brabazon, Nanoparticle production via laser ablation synthesis in solution method and printed electronic application-A brief review, Results Eng., 2022, 16, 100646,  DOI:10.1016/j.rineng.2022.100646.
61. M. E. Shaheen and A. Y. Abdelwahab, Laser ablation in liquids: A versatile technique for nanoparticle generation, Opt. Laser Technol., 2025, 186, 112705,  DOI:10.1016/j.optlastec.2025.112705.
62. V. Harish, M. M. Ansari, D. Tewari, M. Gaur, A. B. Yadav, M. L. García-Betancourt and A. Barhoum, Nanoparticle and nanostructure synthesis and controlled growth methods, Nanomaterials, 2022, 12(18), 3226,  DOI:10.3390/nano12183226.
63. Y. Hatakeyama, K. Onishi and K. Nishikawa, Effects of sputtering conditions on formation of gold nanoparticles in sputter deposition technique, RSC Adv., 2011, 1(9), 1815–1821,  10.1039/c1ra00688f.
64. Y. Wen, D. Xia and W. Xuan, Modeling for particle size prediction and mechanism of silicon nitride nanoparticle synthesis by chemical vapor deposition, Aerosol Sci. Technol., 2017, 51(7), 845–855,  DOI:10.1080/02786826.2017.1307939.
65. B. Richard, J. L. Lemyre and A. M. Ritcey, Nanoparticle size control in microemulsion synthesis, Langmuir, 2017, 33(19), 4748–4757,  DOI:10.1021/acs.langmuir.7b00773.
66. J. S. Benjamin, Dispersion strengthened superalloys by mechanical alloying, Metall. Trans., 1970, 1, 2943–2951,  DOI:10.1007/BF03037835.
67. M. S. El-Eskandarany, A. Al-Hazza, L. A. Al-Hajji, N. Ali, A. A. Al-Duweesh, M. Banyan and F. Al-Ajmi, Mechanical milling: a superior nanotechnological tool for fabrication of nanocrystalline and nanocomposite materials, Nanomaterials, 2021, 11(10), 2484,  DOI:10.3390/nano11102484.
68. A. M. Shi, D. Li, L. J. Wang, B. Z. Li and B. Adhikari, Preparation of starch-based nanoparticles through high-pressure homogenization and miniemulsion cross-linking: Influence of various process parameters on particle size and stability, Carbohydr. Polym., 2011, 83(4), 1604–1610,  DOI:10.1016/j.carbpol.2010.10.011.
69. J. D. Robertson, L. Rizzello, M. Avila-Olias, J. Gaitzsch, C. Contini, M. S. Magoń and G. Battaglia, Purification of nanoparticles by size and shape, Sci. Rep., 2016, 6(1), 27494,  DOI:10.1038/srep27494.
70. G. Tombuloglu, Y. Slimani, H. Tombuloglu, M. Alsaeed, E. A. Turumtay, H. Sozeri and A. Baykal, Impact of sonication time in nanoparticle synthesis on the nutrition and growth of wheat (Triticum aestivum L.) plant, Plant Nano Biol., 2024, 8, 100075,  DOI:10.1016/j.plana.2024.100075.
71. A. Asadi, F. Pourfattah, I. M. Szilágyi, M. Afrand, G. Żyła, H. S. Ahn and O. Mahian, Effect of sonication characteristics on stability, thermophysical properties, and heat transfer of nanofluids: A comprehensive review, Ultrason. Sonochem., 2019, 58, 104701,  DOI:10.1016/j.ultsonch.2019.104701.
72. C. Sauter, M. A. Emin, H. P. Schuchmann and S. Tavman, Influence of hydrostatic pressure and sound amplitude on the ultrasound induced dispersion and de-agglomeration of nanoparticles, Ultrason. Sonochem., 2008, 15(4), 517–523,  DOI:10.1016/j.ultsonch.2007.08.010.
73. X. Sun, S. M. Tabakman, W. S. Seo, L. Zhang, G. Zhang, S. Sherlock and H. Dai, Separation of nanoparticles in a density gradient: FeCo@ C and gold nanocrystals, Angew. Chem., Int. Ed., 2009, 48(5), 939,  DOI:10.1002/anie.200805047.
74. S. H. Lee, B. K. Salunke and B. S. Kim, Sucrose density gradient centrifugation separation of gold and silver nanoparticles synthesized using Magnolia kobus plant leaf extracts, Biotechnol. Bioprocess Eng., 2014, 19, 169–174,  DOI:10.1007/s12257-013-0561-4.
75. Y. Gokce, B. Cengiz, N. Yildiz, A. Calimli and Z. Aktas, Ultrasonication of chitosan nanoparticle suspension: Influence on particle size, Colloids Surf., A, 2014, 462, 75–81,  DOI:10.1016/j.colsurfa.2014.08.028.
76. T. Salafi, K. K. Zeming and Y. Zhang, Advancements in microfluidics for nanoparticle separation, Lab Chip, 2017, 17(1), 11–33,  10.1039/C6LC01045H.
77. S. Gimondi, H. Ferreira, R. L. Reis and N. M. Neves, Microfluidic devices: a tool for nanoparticle synthesis and performance evaluation, ACS Nano, 2023, 17(15), 14205–14228,  DOI:10.1021/acsnano.3c01117.
78. J. D. Judy, J. M. Unrine and P. M. Bertsch, Evidence for biomagnification of gold nanoparticles within a terrestrial food chain, Environ. Sci. Technol., 2011, 45(2), 776–781,  DOI:10.1021/es103031a.
79. S. H. Kim, S. Bae, Y. W. Sung and Y. S. Hwang, Effects of particle size on toxicity, bioaccumulation, and translocation of zinc oxide nanoparticles to bok choy (Brassica chinensis L.) in garden soil, Ecotoxicol. Environ. Saf., 2024, 280, 116519,  DOI:10.1016/j.ecoenv.2024.116519.
80. E. Yusefi-Tanha, S. Fallah, L. R. Pokhrel and A. Rostamnejadi, Role of particle size-dependent copper bioaccumulation-mediated oxidative stress on Glycine max (L.) yield parameters with soil-applied copper oxide nanoparticles, Environ. Sci. Pollut. Res., 2024, 31(20), 28905–28921,  DOI:10.1007/s11356-024-33070-x.
81. Z. Zhang, X. He, H. Zhang, Y. Ma, P. Zhang, Y. Ding and Y. Zhao, Uptake and distribution of ceria nanoparticles in cucumber plants, Metallomics, 2011, 3(8), 816–822,  10.1039/c1mt00049g.
82. X. Ma, J. Geiser-Lee, Y. Deng and A. Kolmakov, Interactions between engineered nanoparticles (ENPs) and plants: phytotoxicity, uptake and accumulation, Sci. Total Environ., 2010, 408(16), 3053–3061,  DOI:10.1016/j.scitotenv.2010.03.031.
83. C. Larue, G. Veronesi, A. M. Flank, S. Surble, N. Herlin-Boime and M. Carrière, Comparative uptake and impact of TiO2 nanoparticles in wheat and rapeseed, J. Toxicol. Environ. Health, 2012, 75(13-15), 722–734.
84. Y. Wang, W. Hui, D. Zhang, X. Chen, R. Wang, Y. Xu and G. He, Absorption and transport of different ZnO nanoparticles sizes in Agrostis stolonifera: Impacts on physiological, biochemical responses, root exudation, and microbial community structure, Plant Physiol. Biochem., 2025, 219, 109369,  DOI:10.1016/j.plaphy.2024.109369.
85. Z. Li, W. Yan, Y. Li, Y. Xiao, Y. Shi, X. Zhang and G. Jiang, Particle size determines the phytotoxicity of ZnO nanoparticles in rice (Oryza sativa L.) revealed by spatial imaging techniques, Environ. Sci. Technol., 2023, 57(36), 13356–13365,  DOI:10.1021/acs.est.3c03821.
86. W. Theerak, P. Ditthakit, T. Puttamuk and P. Chuawong, Effects of size and dose of titanium dioxide on the early development of rice exposed to nanoparticle suspensions, J. Biosyst. Eng., 2023, 48(4), 412–427,  DOI:10.1007/s42853-023-00201-0.
87. N. Al-Amri, H. Tombuloglu, Y. Slimani, S. Akhtar, M. Barghouthi, M. Almessiere and S. Ozcelik, Size effect of iron (III) oxide nanomaterials on the growth, and their uptake and translocation in common wheat (Triticum aestivum L.), Ecotoxicol. Environ. Saf., 2020, 194, 110377,  DOI:10.1016/j.ecoenv.2020.110377.
88. T. N. Prasad, S. Adam, P. Visweswara Rao, B. Ravindra Reddy and T. Giridhara Krishna, Size dependent effects of antifungal phytogenic silver nanoparticles on germination, growth and biochemical parameters of rice (Oryza sativa L), maize (Zea mays L) and peanut (Arachis hypogaea L), IET Nanobiotechnol., 2017, 11(3), 277–285,  DOI:10.1049/iet-nbt.2015.0122.
89. K. M. Singh, A. B. Jha, R. S. Dubey and P. Sharma, Nanoparticle-mediated mitigation of salt stress-induced oxidative damage in plants: insights into signaling, gene expression, and antioxidant mechanisms, Environ. Sci.: Nano, 2025, 12, 2983–3017,  10.1039/D5EN00174A.
90. M. T. El-Saadony, A. M. Saad, S. M. Soliman, H. M. Salem, E. S. M. Desoky, A. O. Babalghith and S. F. AbuQamar, Role of nanoparticles in enhancing crop tolerance to abiotic stress: A comprehensive review, Front. Plant Sci., 2022, 13, 946717,  DOI:10.3389/fpls.2022.946717.
91. F. Gao, X. Zhang, J. Zhang, J. Li, T. Niu, C. Tang and J. Xie, Zinc oxide nanoparticles improve lettuce (Lactuca sativa L.) plant tolerance to cadmium by stimulating antioxidant defense, enhancing lignin content and reducing the metal accumulation and translocation, Front. Plant Sci., 2022, 13, 1015745,  DOI:10.3389/fpls.2022.1015745.
92. R. E. Abdelhameed, H. Abdalla, H. S. Hegazy and M. H. Adarosy, Interpreting the potential of biogenic TiO2 nanoparticles on enhancing soybean resilience to salinity via maintaining ion homeostasis and minimizing malondialdehyde, Sci. Rep., 2025, 15(1), 12904,  DOI:10.1038/s41598-025-94421-3.
93. C. H. Foyer, Reactive oxygen species, oxidative signaling and the regulation of photosynthesis, Environ. Exp. Bot., 2018, 154, 134–142,  DOI:10.1016/j.envexpbot.2018.05.003.
94. A. Nessim and R. El-Shenody, Mitigation of lead stress in Triticum aestivum by seed priming in aqueous extracts of the macroalgae Halimeda opuntia and Codium fragile, Egypt. J. Bot., 2018, 58(2), 263–274.
95. M. H. Siddiqui, S. Alamri, M. Y. Al-Khaishany, M. N. Khan, A. Al-Amri, H. M. Ali and A. A. Alsahli, Exogenous melatonin counteracts NaCl-induced damage by regulating the antioxidant system, proline and carbohydrates metabolism in tomato seedlings, Int. J. Mol. Sci., 2019, 20(2), 353,  DOI:10.3390/ijms20020353.
96. M. Hasanuzzaman, M. B. Bhuyan, F. Zulfiqar, A. Raza, S. M. Mohsin, J. A. Mahmud and V. Fotopoulos, Reactive oxygen species and antioxidant defense in plants under abiotic stress: Revisiting the crucial role of a universal defense regulator, Antioxidants, 2020, 9(8), 681,  DOI:10.3390/antiox9080681.
97. Y. Y. Syu, J. H. Hung, J. C. Chen and H. W. Chuang, Impacts of size and shape of silver nanoparticles on Arabidopsis plant growth and gene expression, Plant Physiol. Biochem., 2014, 83, 57–64,  DOI:10.1016/j.plaphy.2014.07.010.
98. M. Kang, X. Bai, Y. Liu, Y. Weng, H. Wang and Z. Ye, Driving role of zinc oxide nanoparticles with different sizes and hydrophobicity in metabolic response and eco-corona formation in sprouts (Vigna radiata), Environ. Sci. Technol., 2024, 58(22), 9875–9886,  DOI:10.1021/acs.est.4c01731.
99. (a) J. Miliauskienė, A. Brazaitytė, R. Sutulienė, M. Urbutis and S. Tučkutė, ZnO nanoparticle size-dependent effects on swiss chard growth and nutritional quality, Agriculture, 2022, 12(11), 1905,  DOI:10.3390/agriculture12111905.
100. Y. Guo, H. Li, Y. Hao, H. Shang, W. Jia, A. Liang and C. Ma, Size effects of copper oxide nanoparticles on boosting soybean growth via differentially modulating nitrogen assimilation, Nanomaterials, 2024, 14(9), 746,  DOI:10.3390/nano14090746.
101. L. Zhao, Y. Sun, J. A. Hernandez-Viezcas, A. D. Servin, J. Hong, G. Niu and J. L. Gardea-Torresdey, Influence of CeO2 and ZnO nanoparticles on cucumber physiological markers and bioaccumulation of Ce and Zn: a life cycle study, J. Agric. Food Chem., 2013, 61(49), 11945–11951,  DOI:10.1021/jf404328e.
102. X. Luo and Y. He, Experiencing winter for spring flowering: A molecular epigenetic perspective on vernalization, J. Integr. Plant Biol., 2020, 62(1), 104–117,  DOI:10.1111/jipb.12896.
103. B. Gupta and B. Huang, Mechanism of salinity tolerance in plants: physiological, biochemical, and molecular characterization, Int. J. Genomics, 2014, 701596,  DOI:10.1155/2014/701596.
104. A. H. Abeed, A. A. Al-Huqail, S. Albalawi, S. A. Alghamdi, B. Ali, S. M. Alghanem and M. T. El-Mahdy, Calcium nanoparticles mitigate severe salt stress in Solanum lycopersicon by instigating the antioxidant defense system and renovating the protein profile, S. Afr. J. Bot., 2023, 161, 36–52,  DOI:10.1016/j.sajb.2023.08.005.
105. G. Mustafa, K. Sakata and S. Komatsu, Proteomic analysis of soybean root exposed to varying sizes of silver nanoparticles under flooding stress, J. Proteomics, 2016, 148, 113–125,  DOI:10.1016/j.jprot.2016.07.027.
106. G. Mustafa and S. Komatsu, Insights into the response of soybean mitochondrial proteins to various sizes of aluminum oxide nanoparticles under flooding stress, J. Proteome Res., 2016, 15(12), 4464–4475,  DOI:10.1021/acs.jproteome.6b00572.
107. S. W. Przemieniecki, K. Ruraż, O. Kosewska, M. Oćwieja and A. Gorczyca, The impact of various forms of silver nanoparticles on the rhizosphere of wheat (Triticum aestivum L.)-Shifts in microbiome structure and predicted microbial metabolic functions, Sci. Total Environ., 2024, 914, 169824,  DOI:10.1016/j.scitotenv.2023.169824.
108. L. F. Leopold, C. Coman, D. Clapa, I. Oprea, A. Toma, Ş. D. Iancu and V. Coman, The effect of 100-200 nm ZnO and TiO2 nanoparticles on the in vitro-grown soybean plants, Colloids Surf., B, 2022, 216, 112536,  DOI:10.1016/j.colsurfb.2022.112536tomb.
109. J. Geisler-Lee, Q. Wang, Y. Yao, W. Zhang, M. Geisler, K. Li and X. Ma, Phytotoxicity, accumulation and transport of silver nanoparticles by Arabidopsis thaliana, Nanotoxicology, 2013, 7(3), 323–337,  DOI:10.3109/17435390.2012.658094.
110. X. Li, L. Peng, Y. Cai, F. He, Q. Zhou and D. Shi, Potential Threat of Lead Oxide Nanoparticles for food crops: Comprehensive understanding of the impacts of different nanosized PbO x (x= 1, 2) on maize (Zea mays L.) seedlings in vivo, J. Agric. Food Chem., 2023, 71(10), 4235–4248,  DOI:10.1021/acs.jafc.2c06843.
111. M. M. Sarkar, P. Saha, B. Karmakar, P. Toppo, P. Paul, T. K. Dua and S. Roy, Sugar-coating on the surface of silica nanoparticles attenuates the dose-and size-dependent toxicity of the nanoparticles for plant-based applications, Plant Physiol. Biochem., 2025, 223, 109778,  DOI:10.1016/j.plaphy.2025.109778.
112. S. A. Atanda, R. O. Shaibu and F. O. Agunbiade, Nanoparticles in agriculture: balancing food security and environmental sustainability, Discov. Agric., 2025, 3(1), 26,  DOI:10.1007/s44279-025-00159-x.
113. S. Islam, Toxicity and transport of nanoparticles in agriculture: effects of size, coating, and aging, Front. Nanotechnol., 2025, 7, 1622228,  DOI:10.3389/fnano.2025.1622228.
114. K. Basar, K. Doruk, N. Akli, S. Lida and A. Mibang, Nanotechnology in agriculture: Promises, risks and challenges, Int. J. Chem. Stud., 2024, 12(1), 26–28.
115. M. Hosseinifard, N. Jurga, J. C. Brandmeier, Z. Farka, A. Hlaváček, H. H. Gorris and A. Ekner-Grzyb, Influence of surface modification and size of lanthanide-doped upconverting nanoparticles on wheat seedlings, Chemosphere, 2024, 347, 140629,  DOI:10.1016/j.chemosphere.2023.140629.
116. D. Choudhary, S. Deshmukh, G. Maheswari, A. Kumari and V. Ghormade, Silica and mesoporous silica nanoparticles display effective insecticidal effect and augment plant defense responses, Pestic. Biochem. Physiol., 2025, 210, 106389,  DOI:10.1016/j.pestbp.2025.106389.
117. F. Cai, X. Wu, H. Zhang, X. Shen, M. Zhang, W. Chen and X. Wang, Impact of TiO2 nanoparticles on lead uptake and bioaccumulation in rice (Oryza sativa L.), NanoImpact, 2017, 5, 101–108,  DOI:10.1016/j.impact.2017.01.006.

---

Footnote

† Sunil Soni and Km Madhuri Singh contributed equally to this manuscript.

---