Quan-Doan Mai*a,
Dang Thi Hanh Tranga,
Ta Ngoc Bachb,
Vo Thi Le Nac,
Anh-Tuan Phamc and
Anh-Tuan Le
*ac
aPhenikaa University Nano Institute (PHENA), Phenikaa University, Hanoi 12116, Vietnam. E-mail: doan.maiquan@phenikaa-uni.edu.vn; tuan.leanh@phenikaa-uni.edu.vn
bInstitute of Materials Science (IMS), Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi 10000, Vietnam
cFaculty of Materials Science and Engineering (MSE), Phenikaa University, Hanoi 12116, Vietnam
First published on 7th February 2025
Surface-enhanced Raman spectroscopy (SERS) is a renowned analytical technique for non-invasive molecular identification. Advancements in SERS technology pivot on designing nano-structured substrates to enhance sensitivity and reliability. A key emerging trend involves integrating pre-treatment and post-treatment techniques on these substrates, leveraging advanced nanostructures to bring unique features, such as ultrasensitivity or reusability, to bridge the gap between laboratory and real-world applications of the SERS technique. Despite these advances, the synergistic application of pre- and post-treatment techniques on a single SERS substrate to fully exploit unique physicochemical effects remains underexplored. To address this, we introduce photo-induced-photo-catalytic SERS (PI-PC SERS), a novel technique that synergistically combines photo-induced enhanced Raman scattering (PIERS) and photocatalysis using a single Ag/TiO2 nanocomposite structure. This method aims to deliver ultrasensitive sensing capabilities and reusability. The PI-PC SERS technique involves pre-irradiating the SERS substrate with UV light to amplify the Raman signal and post-irradiating to remove fouled analytes. Pre-irradiation enhances the SERS signal by several orders of magnitude compared to normal SERS, attributed to the PIERS effect. Consequently, the detection sensitivity for methylene blue (MB) using PI-PC SERS reaches 1.02 × 10−14 M, significantly better than the 3.04 × 10−11 M achieved with normal SERS. Similar enhancements are observed for thiram, with a limit of detection (LOD) of 1.02 × 10−11 M for PI-PC SERS compared to 2.19 × 10−9 M for normal SERS. Additionally, post-irradiation facilitates the removal of analyte molecules via photocatalysis, restoring the substrate to its pristine state, as the byproducts – water and CO2 gas – are easily managed. Our findings demonstrate that PI-PC SERS creates ultrasensitive sensors and ensures substrate cleanliness and longevity. This method shows great promise for ultrasensitive, sustainable, and cost-effective applications in chemical sensing and molecular diagnostics.
Several advanced techniques leveraging external physical interactions with SERS substrates have been introduced, demonstrating exceptional efficiency. These include heat-induced surface-enhanced Raman scattering (HI-SERS), electric-field-induced surface-enhanced Raman scattering (E-SERS), and the more recent photo-induced enhanced Raman scattering (PIERS). Additionally, photocatalytic activity has been effectively incorporated into SERS substrate engineering to develop reusable substrates aimed at sustainability. Huang et al. introduced the HI-SERS technique, which significantly enhances the SERS signal of glutathione, a biological molecule, by heating silver colloid substrates before measurements.20 This method achieved a LOD value of 50 nM for glutathione, compared to 1 μM with normal SERS techniques, showcasing a substantial improvement in sensing efficiency. Almohammed et al. demonstrated the E-SERS technique by applying an electric field (10–25 V mm−1) to aligned semiconducting peptide nanotube–graphene oxide composite structures during SERS measurements.21 This approach enabled nanomolar detection sensitivity for glucose and nucleobases, with up to a tenfold signal enhancement compared to metal-based substrates. The PIERS technique, as demonstrated by Ben-Jaber et al., showed significantly enhanced sensing efficiency over normal SERS.22 By irradiating metal/semiconductor-structured SERS substrates with UV light before conducting SERS measurements, they observed a substantial increase in the SERS signal of analytes compared to non-irradiated substrates. Wu et al. introduced a reusable SERS substrate based on the photocatalytic activity of Au@Cu2O–Ag nanocomposites.23 After SERS measurements of the analyte malachite green (MG), the Au@Cu2O–Ag substrates were irradiated with UV light, effectively decomposing MG molecules via photocatalysis. This process rejuvenated the SERS substrates, making them ready for subsequent measurements. This innovation addresses the issue of waste associated with single-use SERS substrates due to residual analytes, providing economic and environmental benefits, and aligning with sustainability goals. These advancements underscore the potential of integrating external physical interactions and photocatalytic activity in SERS substrate design, paving the way for ultra-sensitive, reliable, and sustainable sensing technologies.
The effectiveness of the developed techniques surrounding SERS has been convincingly demonstrated. However, each technique has its limitations. For example, HI-SERS requires substrates to sustain high temperatures during pre-treatment, which limits the use of SERS materials and also restricts its applications due to the effect of temperature on heat-sensitive analytes. The E-SERS technique necessitates the application of a continuous electric field during measurements, as the electric field effect disappears immediately after the voltage is removed. This requirement for complex substrate fabrication poses scalability challenges. The PIERS technique can eliminate the need for continuous irradiation during measurement, significantly simplifying experimental procedures. However, it does not address the issue of substrate reusability, as residual analytes remain on the substrate. SERS substrates based on photocatalytically active materials can provide reusability for the substrate; however, this feature alone does not fully exploit the potential of the strong SERS enhancement. Combining these techniques into a single experimental protocol promises to create a SERS substrate with even greater advantages. Among the aforementioned techniques, PIERS and photocatalysis share many similarities and exhibit high potential for synergistic integration within a SERS measurement protocol. Mechanistically, a SERS substrate utilizing the PIERS effect is based on a metal/semiconductor nanocomposite structure.22,24,25 When the semiconductor material is pre-irradiated with UV light, oxygen vacancies can occur on the surface, creating a temporary defect energy level at the metal–semiconductor interface.22 This leads to an increased charge transfer between the metal and the semiconductor, resulting in a significantly enhanced Raman scattering intensity compared to non-irradiated (i.e., normal SERS) scenarios. Meanwhile, the photocatalytic activity of metal/semiconductor nanocomposite materials is highly regarded and well-documented in numerous studies.26–28 This structure significantly increases the number of electrons available to participate in reactions, forming hydroxyl radicals (˙OH) that decompose organic molecules into water and CO2 gas.27,28 Subsequently, the water can be evaporated, and the CO2 gas diffused into the air, restoring the SERS substrate to a pristine state. Based on this foundation, fabricating a SERS substrate using a metal/semiconductor structure and simultaneously applying both pre- and post-irradiation techniques to combine the synergistic effects of PIERS and photocatalysis in a single SERS protocol can result in several key benefits: (i) high sensitivity due to superior signal enhancement, (ii) substrate reusability contributing to cost-effectiveness and sustainability, and (iii) simplified, scalable experimental procedures suitable for diverse sensing applications. By integrating these mechanisms into a single SERS protocol, this technique not only enhances the overall SERS signal but also offers a practical solution for sustainable and reusable SERS substrates, outperforming conventional techniques in terms of sensitivity, simplicity, and long-term practicality.
Herein, inspired by the PIERS and photocatalysis effects of the metal/semiconductor structure, we introduce a novel technique that combines these two effects on a SERS substrate based on Ag (metal)/TiO2 (semiconductor) nanocomposite material, termed photo-induced-photo-catalytic SERS (hereafter abbreviated as PI-PC SERS). This approach yields a SERS substrate with simultaneous ultra-sensitive sensing capabilities achieved by pre-irradiating the Ag/TiO2 substrate with UV light (365 nm) before conducting SERS measurements (PIERS effect), and reusability facilitated by post-irradiation with UV light (365 nm) after SERS measurements (photocatalysis effect). Methylene blue (MB), an organic dye, and thiram, a plant protection agent, were selected as analytes to evaluate the effectiveness of the proposed PI-PC SERS technique. The results demonstrate superior sensor performance of PI-PC SERS compared to normal SERS, with LOD for MB and thiram under PI-PC SERS conditions measured at 1.02 × 10−14 M and 1.02 × 10−11 M, respectively, whereas normal SERS achieves 3.04 × 10−11 M and 2.19 × 10−9 M, respectively. Moreover, the photocatalysis effect was effectively applied to the used Ag/TiO2 SERS substrate to remove fouled analyte molecules (MB or thiram) from its surface. The decomposition of MB and thiram on the Ag/TiO2 substrate was evaluated by monitoring the SERS intensity of these molecules over increasing durations of UV irradiation at 365 nm. The results show complete degradation of MB and thiram residues on the Ag/TiO2 substrate within 60 to 70 minutes of UV irradiation, evidenced by the disappearance of their Raman scattering peaks in the SERS spectra. This process results in a completely refreshed Ag/TiO2 substrate ready for subsequent PI-PC SERS experiments. Clearly, the PI-PC SERS technique not only improves detection sensitivity and substrate longevity but also offers a sustainable and cost-effective solution for high-performance chemical and bio-analytical sensing applications. This advancement represents a significant step forward in enhancing both the practicality and efficiency of SERS technologies.
![]() | ||
Scheme 1 Pre-irradiation procedure of Ag/TiO2 SERS substrate in the PI-PC SERS technique for enhancing the SERS signal via the PIERS effect. |
![]() | ||
Scheme 2 Post-irradiation process of the Ag/TiO2 SERS substrate following SERS measurements to utilize photocatalytic effect for obtaining a renewable Ag/TiO2 substrate. |
Fig. 1 illustrates the results of MB detection under normal SERS conditions (i.e., without pre-irradiation) on the Ag/TiO2 substrate. SERS spectra of MB were acquired across concentrations ranging from 10−4 M to 10−11 M (Fig. 1a). Characteristic peaks of MB are detailed in Table S1 and Fig. S1a (ESI†). The signal intensities of these characteristic peaks are notably pronounced at concentrations of 10−4, 10−5, and 10−6 M, displaying a diminishing trend with decreasing concentration. These peaks are faintly discernible at a concentration of 10−10 M and are absent at 10−11 M (cannot be clearly distinguished with noise signals). Based on the relationship between the SERS intensities at each concentration, the LOD values were calculated for the peaks at 460, 1120, 1410, and 1615 cm−1. The linear correlation between the logarithm of the MB concentration and the SERS intensity of the selected peaks is illustrated in Fig. 1b and S1b–d.† The highest linearity was observed at the 460 cm−1 peak with an R2 value of 0.97 over the concentration range of 10−7 to 10−11 M, while the other peaks exhibited R2 values < 0.9. SERS spectra of MB at different concentrations in the range of 10−7 to 10−11 M were also collected to enhance the accuracy of the linear calibration curve (Fig. S2†). The linear calibration curve, established based on 9 data points (Fig. 1b), yields the equation y = 7.71 + 0.58x. Using this linear equation and the calculation method detailed in the ESI,† the LOD in this case was determined to be 2.89 × 10−11 M. The practical application of the Ag/TiO2 substrate was also evaluated over a 60 day storage period and exhibited high long-term stability when stored away from direct exposure to moisture and light (as detailed in Fig. S3 and the ESI†).
Applying the PIERS effect in the PI-PC SERS technique is anticipated to significantly enhance the efficiency of MB detection. The experiment involved pre-irradiating the Ag/TiO2 substrate with 365 nm UV light for 30 minutes prior to depositing the MB analyte and conducting SERS measurements. The results are depicted in Fig. 2 and 3. The SERS peaks at 460, 508, 890, 1120, 1410, and 1615 cm−1 remain distinctly visible without any notable shifts, indicating that the pre-irradiation process did not affect the molecular vibrations of MB. Notably, the SERS intensity in the PI-PC SERS approach exhibits significant enhancement compared to normal SERS experiment. Fig. 3a and b compare the SERS signals obtained from PI-PC SERS and normal SERS at MB concentrations of 10−6 M and 10−10 M, respectively. At the higher concentration of 10−6 M, the application of the PIERS technique results in approximately a twofold enhancement in SERS intensity compared to normal SERS, while at the lower concentration of 10−10 M, PI-PC SERS demonstrates an impressive 8.8-fold enhancement in SERS signal intensity over normal SERS (comparison of enhancement across the 10−4 to 10−10 M concentration range at the best linear peak, 460 cm−1, is detailed in Table S2†). This notable enhancement enables the Ag/TiO2 substrate with PIERS application to detect clear SERS signals from MB molecules even at an ultra-low concentration of 10−13 M (see Fig. S4†). Sensitivity metrics were calculated, revealing a linear range from 10−9 to 10−14 M with a linear equation of y = 8.70 + 0.55x (Fig. 2b), based on 9 data points collected from SERS spectra of closely spaced concentrations to ensure greater accuracy in the linearity within this range (Fig. S5†). The LOD value was determined to be 1.02 × 10−14 M, which represents an improvement of three orders of magnitude over normal SERS. Furthermore, the reliability of the experiment was assessed through parameters of repeatability and reproducibility. Repeatability was evaluated by measuring five different points on a single Ag/TiO2 substrate after irradiation and subsequent analyte addition (Fig. S6a†). Reproducibility was assessed by performing five separate irradiation and SERS signal collection processes on different Ag/TiO2 substrates (Fig. S6b†). The results demonstrate high experimental reliability, indicated by very low relative standard deviations (RSD) of 5.97% and 6.62% for repeatability and reproducibility, respectively (detailed RSD calculation method in the ESI†). The detection efficiency of MB using the PI-PC SERS technique on the Ag/TiO2 substrate is significantly superior to the normal SERS technique reported on other SERS substrates. Table 1 compares the MB detection efficiency of normal SERS and PI-PC SERS techniques, highlighting significant improvements in sensitivity, with PI-PC SERS achieving a sensitivity of up to 1.02 × 10−14 M.
Substrate | Technique | LOD | Reproducibility | Ref. |
---|---|---|---|---|
Ag–rGO nanocomposite | SERS | 1.00 × 10−8 M | — | 30 |
Ni(OH)2/Ag nanocomposites | SERS | 1.00 × 10−8 M | — | 31 |
Fe3O4/GO/Ag nanocomposite | SERS | 1.00 × 10−9 M | — | 32 |
Au/Cu2O nanocomposite | SERS | 3.40 × 10−12 M | <10% | 33 |
Ag/TiO2 nanocomposite | SERS | 2.89 × 10−11 M | — | This work |
Ag/TiO2 nanocomposite | PI-PC SERS | 1.02 × 10−14 M | 6.62% | This work |
The superior enhancement of SERS signals in the PI-PC SERS technique arises from intricate photo-electro interactions within the Ag/TiO2 transition structure. Fig. 3c and d elucidate the mechanisms in both conventional SERS and PI-PC SERS cases. During SERS measurements, the localized surface plasmon resonance (LSPR) effect in Ag nanoparticles induces charge excitation. These charges are either directly transferred to nearby MB molecules, thereby generating SERS signals, or they interact indirectly via TiO2 intermediates before reaching MB. In normal SERS, excited charges from Ag migrate to the conduction band of TiO2, which lacks electrons. Subsequently, these charges transition to the lowest unoccupied molecular orbital (LUMO) of MB. Charges returning from the LUMO level to the highest occupied molecular orbital (HOMO) of MB amplify Raman scattering signals. The charge transfer and interactions among light, Ag/TiO2 nanocomposites, and MB molecules significantly enhance SERS signals, enabling detection of MB at near-picogram levels (10−11 M). Pre-irradiation of the Ag/TiO2 structure with 365 nm UV light causes surface oxygen atoms on TiO2 to eject, forming oxygen vacancies, as previously demonstrated.22,24,34 Using experimental methods combined with scanning tunneling microscopy, Mezhenny et al. provided evidence of defect formation in TiO2, attributed to the collective removal of oxygen induced by UV light.35 This process generates a transient intermediate energy state (V0 in Fig. 3d) within the TiO2 electronic structure. Henrich et al. identified that this V0 state generates energy levels located approximately 0.7 eV below the minimum conduction band edge of TiO2.36 This temporary state facilitates charge transfer from Ag to TiO2, thereby enhancing the probability and number of charges transferred to surrounding MB molecules near the Ag/TiO2 nanostructure.22,37,38 Consequently, this enhancement results in significantly boosted SERS signals compared to normal SERS techniques. However, the ability to maintain the PIERS effect after ceasing the irradiation source needs to be assessed, as oxygen vacancies may be filled by oxygen molecules from the air. This phenomenon of surface healing has been demonstrated by the ability of the TiO2 surface to adsorb O2 or H2O molecules from the air, thereby filling the oxygen vacancies.39 An experiment evaluating the stability of the PIERS effect on the Ag/TiO2 substrate was performed by collecting SERS spectra at various time intervals following the pre-irradiation process to further confirm this surface healing phenomenon on the TiO2 surface. The results are presented in Fig. S7† and the analysis provided in the ESI† shows that the SERS signal gradually decreased over time as the SERS was exposed to air, which indirectly supports the formation of oxygen vacancies on TiO2.
In practical terms, once SERS signals have been collected, the SERS substrates are typically rendered unusable due to the accumulation of analyte molecules on their surfaces. Removing these analytes through conventional methods such as washing or thermal decomposition is nearly impractical due to their molecular-level adhesion, which directly affects the substrate's quality. Therefore, reusing SERS substrates to achieve goals such as cost reduction and sustainability poses significant challenges. Apart from successfully exploiting the PIERS effect in Ag/TiO2 nanostructures as demonstrated earlier, the photocatalytic activity of this structure can be further utilized to provide additional advantages for SERS substrates based on Ag/TiO2. If applying pre-UV irradiation at 365 nm has already shown effective improvements in the sensing performance for detecting MB, subsequent UV irradiation at 365 nm could enable self-regeneration of Ag/TiO2 substrates through photocatalytic activity (details described in the Methods section). The Ag/TiO2 SERS substrate, after SERS signal collection, is moistened with water and then subjected to UV irradiation at 365 nm (UV region capable of activating TiO2 photocatalytic effects). SERS signals from this irradiated substrate are continuously recorded at different time intervals during the post-irradiation period, as shown in Fig. 4a. At time point 0 minutes, the SERS signal of MB at a concentration of 10−5 M before irradiation is depicted. Subsequent time points (5, 10, 20 minutes, etc.) show the SERS results of MB after irradiation. It is evident that the intensity of MB's characteristic peaks decreases gradually over the irradiation period, indicating molecular degradation of MB and consequent weakening of molecular bonds. After just 70 minutes of irradiation, MB's characteristic peaks have completely disappeared (as further observed in Fig. S8†), indicating that MB has been degraded to a level where it no longer interferes with the SERS signal on the Ag/TiO2 substrate. Fig. 4b succinctly describes the photocatalytic mechanism of MB degradation on Ag/TiO2 following UV irradiation at 365 nm. Electrons excited by the appropriate wavelength in TiO2 nanomaterial generate electron–hole pairs, which can react with water and environmental oxygen to produce hydroxyl radicals (˙OH).40 These radicals possess the capability to directly oxidize MB molecules, breaking them down into the primary products of water and CO2.40,41 This explains why the SERS spectra obtained during photocatalysis do not exhibit additional scattering peaks, as CO2 can readily diffuse away from the substrate surface, and water molecules do not contribute to Raman signals. Although the MB molecule contains nitrogen (N), sulfur (S), and chlorine (Cl), the degradation products may include these elements, but they are present as monatomic or simple molecular forms. This also does not interfere with the overall SERS spectrum. The presence of Ag nanoparticles enhances the photocatalytic efficiency for MB degradation by facilitating electron transfer between TiO2 and Ag, thereby minimizing electron–hole recombination and maximizing the number of active electron–hole pairs involved in the reaction. These synergistic interactions within the Ag/TiO2 composite accelerate MB degradation on the SERS substrate, achieving significant decomposition within a mere 70 minutes of irradiation. Ultimately, this process yields a fully regenerated Ag/TiO2 SERS substrate, preserving the original characteristics necessary for subsequent SERS experiments. We term this advantage as renewable ability.
After surface cleaning via the photocatalytic effect, the renewable ability of the Ag/TiO2 substrate was evaluated through its cyclability using the PI-PC SERS technique. This was tested by detecting MB at a concentration of 10−6 M over five cycles, following the PI-PC SERS protocol detailed in section 2.5. The byproducts of the photocatalytic process, such as water and CO2, could potentially interfere with the reusability of the Ag/TiO2 substrate. Therefore, after the photocatalytic degradation of MB, the Ag/TiO2 substrate was treated at a temperature of 40 °C for 2 hours to evaporate water and CO2 generated during the self-cleaning process. The results are presented in Fig. S9.† The data show that the SERS signals obtained from MB across the different cycles are consistent and comparable to those from the initial use (Fig. S9a and b†). This demonstrates that the PI-PC SERS protocol exhibits excellent cyclability, with no significant decline in sensing performance over multiple cycles.
The efficacy of normal SERS sensing on the renewable Ag/TiO2 substrate has been demonstrated to persist for thiram. A critical inquiry arises regarding the sustained efficacy of the PI-PC SERS technique on this substrate. The PI-PC SERS experiment commenced with pre-irradiating the Ag/TiO2 substrate using 365 nm UV light for 30 minutes, followed by the introduction of the thiram onto the substrate and immediate collection of SERS signals thereafter. The efficacy of thiram detection using PI-PC SERS is illustrated in Fig. 6. The distinctive peaks of thiram are vividly resolved and sharply defined. Notably, the SERS signal intensity obtained surpasses that of normal SERS. At a concentration of 10−6 M (Fig. 7a), the SERS signal from PI-PC SERS is 1.75 times higher than that from normal SERS, rising to 8.68 times at 10−9 M (Fig. 7b). While the characteristic SERS peaks vanish completely at 10−9 M concentration for normal SERS, those at 450, 570, and 1386 cm−1 persist at 10−10 M concentration for PI-PC SERS. The 450 cm−1 peak exhibits an excellent linear correlation between concentration and SERS intensity with an R2 value of 0.99 (Fig. 6b and S12†). The linear range spans from 10−8 M to 10−11 M with a linear equation of y = 7.42 + 0.59x, and the calculated LOD is 1.24 × 10−11 M, two orders of magnitude superior to that of normal SERS. The reliability of the PI-PC SERS experiment on the Ag/TiO2 substrate for thiram analysis is further evaluated through parameters of repeatability and reproducibility (Fig. S13a and b†). The results demonstrate high reliability with RSD values for repeatability and reproducibility of 5.68% and 7.58%, respectively.
Table 2 compares the detection efficiency of thiram on various SERS substrates using normal SERS and PI-PC SERS techniques, showing a significant improvement in sensitivity with PI-PC SERS, achieving a LOD of 10−11 M. The mechanism underlying the amplified SERS signal of the PI-PC SERS technique relative to normal SERS is elucidated in Fig. 7c and d. The occurrence of oxygen vacancies on the TiO2 surface induced by UV irradiation generates an intermediate energy level between the valence and conduction bands of TiO2, thereby enhancing the probability and number of charge transfer from Ag to TiO2, subsequently to thiram. This cascade effect culminates in higher SERS signals from the PI-PC SERS technique.
Substrate | Technique | LOD | Reproducibility | Ref. |
---|---|---|---|---|
Ag@ZIF-67 nanocomposite | SERS | 1.00 × 10−8 M | — | 42 |
Fe3O4@Au nanocomposites | SERS | 7.69 × 10−9 M | — | 43 |
MXene/AgNs nanocomposite | SERS | 1.00 × 10−8 M | 2.22% | 44 |
MoS2-NS@Ag-NP nanocomposite | SERS | 4.20 × 10−8 M | 45 | |
Ag/TiO2 nanocomposite | SERS | 2.06 × 10−9 M | — | This work |
Ag/TiO2 nanocomposite | PI-PC SERS | 1.24 × 10−11 M | 7.58% | This work |
The renewable and reusable capabilities of the Ag/TiO2 SERS substrate were further assessed following sensor signal acquisition with thiram. The photocatalytic outcomes under 365 nm UV irradiation in the presence of water are presented in Fig. 8. It is apparent that the SERS signal from thiram gradually diminishes over the duration of post-irradiation. After 60 minutes of irradiation and photocatalytic activity, the Ag/TiO2 SERS substrate demonstrates cleanliness as the thiram SERS signal completely vanishes, revealing only the scattering peaks of the Ag/TiO2 substrate material (Fig. 8a). The photocatalytic degradation mechanism for thiram is elucidated in Fig. 8b, akin to the degradation pathway observed for MB, driven by the formation of ˙OH radicals proficient in decomposing adjacent organic molecules. The resultant products, water and CO2 gas, facilitate vaporization, thereby facilitating the regeneration of a pristine Ag/TiO2 substrate, primed for reuse in subsequent applications. Thus, the PI-PC SERS technique has been rigorously appraised and has exhibited consistent efficacy in thiram analysis, showcasing both amplified SERS performance via the PIERS effect and rejuvenation capacity through photocatalytic mechanisms. The demonstrated feasibility and efficacy across multiple usage cycles underscore the PI-PC SERS technique introduced in this study as highly promising for practical applications.
Footnote |
† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra07718k |
This journal is © The Royal Society of Chemistry 2025 |