Spectroscopy Intensity Research Articles

Suspended-core photonic crystal fibers for SERS detection of biomolecules

Abstract Photonic crystal fiber (PCF) can be used as a microfluidic platform for surface-enhanced Raman spectroscopy (SERS)-based measurement of different samples. PCF can provide a long area of interaction for light, metal nanoparticles, and analytes incorporated into its holes. This paper provides a COMSOL simulation model for suspended-core PCF used to evaluate the SERS intensity depending on the fiber's geometry and nanoparticles' coverage density. The simulation is applied to compare three PCFs with varying sizes and lengths. SERS measurements of adenine and DNA validate the simulation outcomes and demonstrate the potential of PCFs for SERS-based detection of diverse samples.

Serum metabolic fingerprinting on Ag@AuNWs for traumatic brain injury diagnosis.

Accurate and rapid diagnosis of traumatic brain injury (TBI) is essential for high-quality medical services. Nonetheless, the current diagnostic platform still has challenges in rapidly and accurately analysing clinical samples. Here, we prepared a highly stable, repeatable and sensitive gold-plated silver core-shell nanowire (Ag@AuNWs) for surface-enhanced Raman spectroscopy (SERS) metabolic fingerprint diagnosis of TBI. The core-shell structure significantly enhanced SERS intensity and enables the direct detection of 10 μL serum within seconds. The principal component analysis-linear discriminant analysis (PCA-LDA) and partial least squaresdiscriminant analysis (PLS-DA) are used to evaluate the classification effect of this technology on TBI, respectively. The diagnosis accuracy rate of PCA-LDA and PLS-DA is 73.3% and 86.7% for diagnosing TBI, respectively. Consequently, the PLS-DA model is the optimal selection for distinguishing between the TBI and sham groups. This research will facilitate the application-oriented creation of novel materials with tailored structural designs and the formulation of innovative precision medical protocols in the imminent future.&#xD.

An aptamer sensor based on AgNPs@MOF for surface-enhanced Raman spectroscopy detection of sulfadimethoxine in food.

Ahighly sensitive aptamer sensor (aptasensor) is proposedbased on metal-organic frameworks-silver nanoparticles (AgNPs@MOF) to detect sulfadimethoxine (SDM) by surface-enhanced Raman spectroscopy (SERS). AgNPs@MOF with SERS activity was successfully fabricated by synthesizing AgNPs in situ on the surface of MIL-101(Fe), and SDM aptamer and Raman reporter 4-aminophenthiophenol (4-ATP) were selected as specific recognition elements and signal probes, respectively. When SDM was absent, the SDM aptamers were effectively adsorbed on the surface of AgNPs@MOF, thus keeping AgNPs@MOF in a dispersed state, resulting in a weakened SERS signal of 4-ATP. In the presence of SDM, the combination of SDM and aptamer formed a rigid hairpin SDM-aptamer complex, which bound less to AgNPs@MOF. Therefore, fewer aptamers were adsorbed on AgNPs@MOF, which exposed more hot spots, resulting in an enhanced SERS signal of 4-ATP. The aptasensor had good selectivity and sensitivity towards SDM and a good linear relationship between SERS intensity and SDM concentration in the range 6.00-150.00 ng/mL, with the limit of detection as low as 2.73 ng/mL. Further application to honey and chicken samples spiked with SDM resulted in satisfactory recoveries, and the aptasensor showed good stability and reproducibility in real samples. The aptasensor based on AgNPs@MOF was proposed for the first time to detect trace SDM by SERS, which provided a favorable way to develop various sensing platforms for antibiotic detection in food safety.

Polydopamine Inspired Silver Nanoflower SERS Substrate for Highly Sensitive Detection of Nivalenol in Food Samples: Unveiling Biocompatibility in Mammalian Cells

Surface-enhanced Raman spectroscopy (SERS) is a reliable analytical technique for mycotoxins' swift and precise determination. However, thus far, there has been no exploration of SERS for the quantitative detection of nivalenol (NIV). In this study, we engineered polydopamine-coated silver nanoflower (PDA-AgNFs) SERS substrates with potent "hot spots" to enhance Raman signals of NIV. These substrates exhibited exceptional SERS enhancement capabilities in detecting and quantifying the target analyte, demonstrating uniformity (with a relative standard deviation of SERS signals, RSD = 4.1% for substrate-to-substrate test and 3.24% for spot-to-spot test), an enhancement factor of 2.87 × 10^6 for rhodamine 6B (R6G), and detection sensitivity as low as 1 femtomolar (10^-15 M) for R6G probe molecule. Furthermore, we successfully employed the PDA-AgNFs SERS substrates for the first time to detect NIV in corn, horse beans, and mushroom samples. The calibration curve exhibited a satisfactory linear fit based on SERS intensities at different NIV concentrations, with a detection limit (LOD) of 0.22 nM (S/N = 3) for the proposed approach. Intriguingly, the MTT assay experiment demonstrated the biocompatibility of PDA-AgNFs, showing no toxicity against mammalian NIH-3T3 cells. These biocompatible substrates, endowed with intense plasmonic effects and binding sites, showcased remarkable Raman enhancement, offering an efficient, label-free, and rapid SERS-based analysis of NIV in real samples. Keywords: Polydopamine-inspired, silver nanoflowers, mycotoxins, nivalenol, biocompatibility. Figure 1

SERS calibration substrate with a silent region internal standard for reliable simultaneous detection of multiple antibiotics in water

As the extensive use of antibiotics has led to the rapid spread of antibiotic resistance, there is an urgent need for quantitative assessment of antibiotic residues in the environment. Surface-enhanced Raman spectroscopy (SERS) has emerged as a rapid and cost-effective detection method, but it suffers from the high variability in signal intensities, its quantitative detection remains challenging. Herein, we have developed a SERS calibration substrate with a silent region internal standard, enabling simultaneous and reliable quantitative detection of three commonly antibiotics of penicillin potassium (PP), tetracycline hydrochloride (TCH) and levofloxacin (LEV). The calibration substrate is made by assembling Au @ 4-mercaptobenzonitrile (4-MBN) @ SiO2 on silicon wafer. The chemically-inert silica shell allows the substrate to remain SERS active for more than 24 weeks in the air. The vC ≡ N of 4-MBN in the silent region of 1800–2800 cm−1 provides an effective reference for correcting Raman signal fluctuations. The relative SERS intensity by normalizing to the internal standard (IS) of vC ≡ N shows a linear response against to the logarithmic concentration with a correlation coefficient of 0.997, 0.976, 0.998 and a limit of detection (LOD) of 26.9, 28.2, 2.4 nM for PP, TCH and LEV, respectively. Furthermore, simultaneous detection and principal component analysis (PCA) of these antibiotics in lake water with a concentration range of 1–100 mg/L can achieve a sensitivity and specificity of 100 %. This novel quantitative technique of using this SERS calibration substrate shows promises as a high-throughput platform for multiple trace antibiotics analysis.

Effect of surface charge on laser-produced silver nanoparticles for dye reduction and surface-enhanced Raman spectroscopy

Silver nanoparticles (Ag NPs) are widely used in biological, chemical, and physical fields due to their distinct properties. However, the effect of surfactants with different polarities on the catalytic and surface-enhanced Raman spectroscopy (SERS) performance of Ag NPs has not been thoroughly studied. Here, we tailor the surface charge of laser-synthesized Ag NP without changing their morphology and investigate their catalytic and SERS capabilities. The surfactant-free silver nanoparticles (NPBare), synthesized via pulsed laser ablation in liquid (PLAL), are subsequently coated with ionic surfactants sodium dodecyl sulfate (NPSDS) and cetyltrimethylammonium bromide (NPCTAB). The synthesis and morphology of Ag NPs are confirmed using UV–Vis absorption spectroscopy and scanning electron microscopy. The surface charge of fabricated NPs is determined using zeta potential (ZP) measurements. The ZP values of NPBare, NPSDS, and NPCTAB are determined to be −17 mV, 28.7 mV, and 5.58 mV, respectively. The catalytic activity of bare and coated Ag NPs was tested against the cationic and anionic dyes, Methylene blue (MB) and Methyl orange (MO) respectively. The reduction rate of both dyes was highest when using NPBare. However, in the case of coated nanoparticles, the rate of MB and MO reduction depends on the difference between the ZP of the dye and nanoparticles: the rate of reduction increases with the difference between the zeta potentials of the dye and coated nanoparticles increases. The SERS capability of bare and coated NPs was evaluated for anionic (MO) and cationic (MB, Rhodamine B, and Crystal Violet) dyes. The SERS intensity of dyes strongly enhanced with the increase in ZP difference between the dye molecules and NPs. Surface charge modified NPs shown excellent SERS sensitivity with detection limit up to nanomolar for dye molecules as well as the homogeneity of NPs demonstrated in Raman mapping results with relative standard deviation of 17 %. The results suggest that the electrostatic interaction between the nanoparticles and dye molecules plays a dominant role in SERS enhancement. These findings highlight the significance of surface charge in improving the catalytic and sensing properties of noble metal nanoparticles.

Multiwavelength Surface-Enhanced Raman Scattering Fingerprints of Human Urine for Cancer Diagnosis.

Label-free surface-enhanced Raman spectroscopy (SERS) is capable of capturing rich compositional information from complex biosamples by providing vibrational spectra that are crucial for biosample identification. However, increasing complexity and subtle variations in biological media can diminish the discrimination accuracy of traditional SERS excited by a single laser wavelength. Herein, we introduce a multiwavelength SERS approach combined with machine learning (ML)-based classification to improve the discrimination accuracy of human urine specimens for bladder cancer (BCa) diagnosis. This strategy leverages the excitation-wavelength-dependent SERS spectral profiles of complex matrices, which are mainly attributed to wavelength-related vibrational changes in individual analytes and differences in the variation ratios of SERS intensity across different wavelengths among various analytes. By capturing SERS fingerprints under multiple excitation wavelengths, we can acquire more comprehensive and unique chemical information on complex samples. Further experimental examinations with clinical urine specimens, supported by ML algorithms, demonstrate the effectiveness of this multiwavelength strategy and improve the diagnostic accuracy of BCa and staging of its invasion with SERS spectra from increasing numbers of wavelengths. The multiwavelength SERS holds promise as a convenient, cost-effective, and broadly applicable technique for the precise identification of complex matrices and diagnosis of diseases based on body fluids.

Multiplexed SERS Detection of Serum Cardiac Markers Using Plasmonic Metasurfaces.

Surface-enhanced Raman spectroscopy (SERS) possesses exquisite molecular-specific properties with single-molecule sensitivity. Yet, translation of SERS into a quantitative analysis technique remains elusive owing to considerable fluctuation of the SERS intensity, which can be ascribed to the SERS uncertainty principle, a tradeoff between "reproducibility" and "enhancement". To provide a potential solution, herein, an integrated multiplexed SERS biosensing strategy is proposed, which features two distinct advantages. First, a subwavelength-structured plasmonic metasurface consisting of alternately stacked metal-dielectric pyramidal meta-atoms is fabricated and could provide simultaneously enhanced electric and magnetic fields to enable spatially extended and weakly wavelength-dependent SERS. Second, nanomechanical perturbations are harnessed to transduce signals in the form of SERS frequency shifts, which are not directly affected by the SERS uncertainty principle. By also employing 3D printing methods, a proof-of-concept study of multiplexed detection of a panel of serum cardiac biomarkers for acute myocardial infarction is provided. Success in the development of both the electric and magnetic fields-active plasmonic metasurfaces could transform future designs of SERS substrates with newly endowed functionalities, and frequency shift-based SERS multiplexing could open new opportunities to develop innovative quantitative optical techniques for applications in chemistry, biology, and medicine.

Charge Transfer‐Induced SERS Enhancement of MoS2/Dopants Dependent on their Interaction Difference

Abstract2D transition metal dichalcogenide materials have attracted increasing attention as active surface‐enhanced Raman spectroscopy (SERS) platforms. In this study, the influence of n‐ and p‐type doping of exfoliated MoS2 (exMoS2) hybrids on the SERS performance is investigated, employing Rhodamine 6G (R6G) as a probe molecule. It is demonstrated that n‐doped exMoS2 hybrids (exMoS2 mixed with C60, graphene, and sodium dodecyl sulfate) exhibit enhanced SERS intensities, while p‐doping (exMoS2 mixed with TCNQ) resulted in inhibited SERS enhancement. A key discovery is the linear relationship between Raman enhancement of MoS2/dopant hybrids and the difference in their LUMO energy levels, which dictate the degree and direction of charge transfer. Interestingly, MC60‐4, a C60‐doped hybrid, deviates from the linear relationship, displaying remarkable SERS enhancement owing to its chemical interaction and unique Raman scattering activity. The findings provide critical insights into the SERS enhancement behavior of doped MoS2, facilitating precise tuning of SERS intensities by manipulating the MoS2 doping state.

Pushing the Limits of Lateral Flow Immunoassay by Digital SERS for the Ultralow Detection of SARS‐CoV‐2 Virus

Lateral flow immunoassays (LFIAs) are easy‐to‐use antigen tests that provide different signal readouts, with colorimetric readouts being the most commonly used. However, these analytical devices have relatively low sensitivity and produce semiquantitative results, limiting their diagnostic applications. Herein, we address these challenges by implementing a digital surface‐enhanced Raman spectroscopy (SERS)‐based LFIA for the accurate and ultrasensitive quantitative detection of SARS‐CoV‐2 nucleocapsid (N) protein. Compared with average SERS intensity measurements, the digital approach allowed to overcome fluctuations in Raman scattering signals, thereby increasing the analytical sensitivity of the assay. Our method exhibited a quantification range of the viral protein in nasal swabs from 0.001 to 10 pg mL−1, and a limit of detection down to 1.9 aM (0.9 fg mL−1), improving colorimetric LFIAs and conventional‐SERS‐based LFIAs by several orders of magnitude. Importantly, this approach shows an analytical sensitivity of 0.03 TCID50 mL−1, which is greater than that reported by other immunoassays. In conclusion, we successfully demonstrate the robust detection and quantification of SARS‐CoV‐2N protein in nasal swabs at ultralow concentrations. The improvement in the sensitivity of LFIA by digital SERS may pave the way to translate this technology into the diagnostic arena for the ultrasensitive detection of microbes and disease biomarkers.

A SERS-based point-of-care testing approach for efficient determination of diquat and paraquat residues using a flexible silver flower-coated melamine sponge

Diquat (DQ) and paraquat (PQ) residues in food are potential hazards to consumers' health. Point-of-care testing (POCT) of them remains challenging. Based on surface-enhanced Raman spectroscopy (SERS) technology, we developed a POCT strategy for DQ and PQ on apple surface and in apple juice. A point-of-use composite was fabricated using a piece of porous melamine sponge (MS) modified with silver nanoflowers (AgNFs), combining the specificity of the SERS fingerprint and the excellent adsorption capacity of MS. Using this dual-functional AgNFs@MS, the on-site determination of the DQ and PQ residues was completed within 3 min without pretreatment. Clear trends were observed between SERS intensity and logarithmic concentrations, with r values from 0.962 to 0.984. The limit of detection of DQ and PQ were 0.14–0.70 ppb in apple juice and on apple surface. This study provides a new point-of-use alternative for rapidly detecting DQ and PQ residues in nonlaboratory settings.

Potential powered EC-SERS for sensitive detection of acetamiprid

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for rapid and sensitive detection of pesticide residues in food, and the applied potential regulated SERS technique can be endowed with a higher sensitivity. In this work, we developed an electrochemical-surface enhanced Raman spectroscopy (EC-SERS) sensor for the rapid detection of acetamiprid (AAP) in vegetables. AuNPs/ITO were prepared via in-situ electrodeposition of gold nanoparticles (AuNPs) on an indium tin oxide (ITO) both as a SERS substrate and working electrode. By adding AAP into an in-situ Raman electrolytic cell with an applied electrochemical potential (+0.3 V), the SERS intensity was enhanced by 4-fold and the characteristic signal was linearly related to the concentration of AAP. Under the optimal conditions, the EC-SERS method exhibited a linear detection range from 0.05 to 50 μM, with a limit of detection (LOD, 3S/M) of 0.02 μM. Simultaneously, based on density functional theory (DFT), the adsorption characteristics of AAP on AuNPs/ITO were studied in the presence of electric field. The method was finally confirmed by HPLC-MS for the detection of real samples, revealing its potential application in food safety.

Surface-enhanced Raman spectroscopy (SERS) substrate based on gold nanostars–silver nanostars for imidacloprid detection

Surface-enhanced Raman spectroscopy (SERS) is a powerful molecular spectroscopy technique that combines Raman spectroscopy with nanostructured metallic surfaces to amplify the Raman signals of target molecules by more than 103. The high sensitivity of SERS poses a significant opportunity for pesticide detection in complex matrices at ultralow concentrations. In this study, we improved the SERS sensitivity for imidacloprid (IMD) by employing silver nanostars (AgNs) coated with gold nanostars (AuNs) as the SERS-active substrate. The SERS response towards IMD detection increased based on the combination of AuNs and AgNs on the substrate surface. The intensity of the SERS signal of IMD using the AuNs/AgNs substrate increased compared to using individual metal nanoparticle substrates. The excellent reproducibility of SERS intensity using the AuNs/AgNs substrate was achieved with a low relative standard derivative (RSD) of 4.87% for 20 different spots on the same sample and 5.19% for 20 different samples. This detection system can be used for multiple tests, which is crucial for the advancement of handheld sensors designed for field use, where minimal or no high-level technical support is accessible.

An economical, high-throughput protein-protein interaction modulator drug screening technique based on surface-enhanced Raman scattering

Increasing identification of protein-protein interaction (PPI) targets creates opportunities for drug discovery. However, the current drug screening strategies are costly and reagent-consuming, which hinders the progress in PPI modulator drug discovery. The primary obstacle lies in the inability to achieve molecular fishing with existing technology. Herein, we present a novel high-throughput, homogeneous-phase screening assay for PPI modulator discovery called “SERScreen”, based on a magnetic field-amplified surface-enhanced Raman spectroscopy (SERS). Two high-affinity proteins are fixed respectively on the magnetic beads (MBs) and the SERS tags, and the cross-linking of two nanoprobes induced by PPI enables strong SERS signals. Candidate modulators interfere with the PPI according to higher affinity toward one protein, resulting in a significant reduction in SERS intensity above the MBs. We established a potential drug screening platform for PD-1/PD-L1, and demonstrated its feasiblility not only with known inhibitors (Durvalumab and BMS-202), but also with a small-molecule combinatorial library, successfully identifying two new candidate inhibitors via the molecular fishing of SERScreen. Furthermore, the anticancer mechanism of two candidates was discussed. As an ultrasensitive, low reagent consumption (2 µL sample solution), high-throughput screening technique in the PPI modulator discovery, SERScreen offers an effective solution for molecular fishing from complex samples and displays high compatibility with automatic measurement equipment.

Adaptive Gap-Tunable Surface-Enhanced Raman Spectroscopy.

Gap plasmon (GP) resonance in static surface-enhanced Raman spectroscopy (SERS) structures is generally too narrow and not tunable. Here, we present an adaptive gap-tunable SERS device to selectively enhance and modulate different vibrational modes via active flexible Au nanogaps, with adaptive optical control. The tunability of GP resonance is up to ∼1200 cm-1 by engineering gap width, facilitated by mechanical bending of a polyethylene terephthalate substrate. We confirm that the tuned GP resonance selectively enhances different Raman spectral regions of the molecules. Additionally, we dynamically control the SERS intensity through the wavefront shaping of excitation beams. Furthermore, we demonstrate simulation results, exhibiting the mechanical and optical properties of a one-dimensional flexible nanogap and their advantage in high-speed biomedical sensing. Our work provides a unique approach for observing and controlling the enhanced chemical responses with dynamic tunability.

Quantitative detecting low concentration polystyrene nanoplastics in aquatic environments via an Ag/Nb2CTx (MXene) SERS substrate

In this study, the plasmonic Ag nanoparticles (Ag NPs) were uniformly anchored on the high conductivity Nb2CTx (MXene) nanosheets to construct an Ag/Nb2CTx substrate for surface-enhanced Raman spectroscopy (SERS) detection of polystyrene (PS) nanoplastics. The KI addition (0.15 mol/L), the volume ratio between substrate colloid and nanoplastic suspension (2:1), and the mass ratio of Nb2CTx in substrate (14%) on SERS performance were optimized. The EM hot spots of Ag/Nb2CTx are significantly enlarged and enhanced, elucidated by FDFD simulation. Then, the linear relationship between the PS nanoplastics concentration with three different sizes (50, 300, and 500 nm) and the SERS intensity was obtained (R2 > 0.976), wherein, the detection limit was as low as 10−4 mg/mL for PS nanoplastic. Owing to the fingerprint feature, the Ag/Nb2CTx-14% substrate successfully discerns the mixtures from two-component nanoplastics. Meanwhile, it exhibits excellent stability of PS nanoplastics on different detection sites. The recovery rates of PS nanoplastics with different sizes in lake water ranged from 94.74% to 107.29%, with the relative standard deviation (RSD) ranging from 2.88% to 8.30%. Based on this method, the expanded polystyrene (EPS) decomposition behavior was evaluated, and the PS concentrations in four water environments were analyzed. This work will pave the way for the accurate quantitative detection of low concentration of nanoplastics in aquatic environments.

Development of a SERS aptasensor for the determination of L-theanine using a noble metal nanoparticle-magnetic nanospheres composite.

An ultrasensitive surface-enhanced Raman spectroscopy (SERS) aptamer sensor (aptasensor) using a noble metal nanoparticle-magnetic nanospheres composite was developed for L-theanine detection. It makes use of Fe3O4@Au MNPs and Au@Ag NPs embedded with the Raman reporter 4-mercaptobenzoic acid (4MBA). Au@4MBA@Ag NPs modified by aptamer and Fe3O4@Au MNPs modified by cDNA created the aptasensor with the strongest Raman signal of 4MBA through the specific binding of the aptamer. With the preferred binding of L-theanine aptamer to L-theanine, Au@4MBA@Ag NPs were released from Fe3O4@Au MNPs, causing a linear decrease in SERS intensity to achieve the SERS detection of the L-theanine. The SERS peak of 4MBA at 1078cm-1 was used for quantitative determination. SERS intensity showed a good log-linear relationship within the range 10-10 to 10-6Mof L-theanine. Theaptasensor has a high selectivityfor L-theanine compared with other twelve testedanalytes. Hence, thisaptasensor is a promising analytical tool for L-theanine detection. The developedmethod was appliedto the analysis of real samples, demonstrating excellent performance. The comparison with the standard liquid chromatography mass spectrometry methodshowed an error within 20%.

Determination of Aminophylline in Human Serum Using Hydrogel Microspheres for Coupled Surface-Enhanced Raman Spectroscopy (SERS) and Solid-Phase Extraction.

Aminophylline (AMP) is a bronchodilator. The therapeutic and toxic doses are very close. Therefore, therapeutic drug monitoring (TDM) of AMP is essential in clinical practice. Microgels were synthesized by free radical precipitation polymerization. Silver@poly(N-isopropyl acrylamide) (Ag@PNIPAM) hybrid microgels were obtained by loading silver (Ag) nanoparticles into the three-dimensional network of the microgels by in situ reduction. The microgel is a three-dimensional reticular structure with tunable pore size, large specific surface area, and good biocompatibility, which can be used as a sorbent for solid-phase extraction (SPE) of target molecules in complex matrices and as a surface-enhanced Raman spectroscopy (SERS) substrate. We optimized the conditions affecting SERS enhancement, such as silver nitrate (AgNO3) concentration and SPE time, according to the SERS strategy of Ag@PNIPAM hybrid microgels to achieve label-free TDM for trace AMP in human serum. The results showed good linearity between the logarithmic concentration of AMP and its SERS intensity in the range of 1-1.1 × 102 µg/mL, with a correlation coefficient (R2) of 0.9947 and a low detection limit of 0.61 µg/mL. The assay accuracy was demonstrated by spiking experiments, with recoveries ranging from 93.0 to 101.8%. The method is rapid, sensitive, reproducible, requires simple sample pretreatment, and has good potential for use in clinical treatment drug monitoring.

Facile synthesis of gold nanostars for the duplex detection of pesticide residues in grapes using SERS.

In recent years, concerns have been raised regarding the contamination of grapes with pesticide residues. As consumer demand for safer food products grows, regular monitoring of pesticide residues in food has become essential. This study sought to develop a rapid and sensitive technique for detecting two specific pesticides (phosmet and paraquat) present on the grape surface using the surface-enhanced Raman spectroscopy (SERS) method. Gold nanostars (AuNS) particles were synthesized, featuring spiky tips that act as hot spots for localized surface plasmon resonance, thereby enhancing Raman signals. Additionally, the roughened surface of AuNS increases the surface area, resulting in improved interactions between the substrate and analyte molecules. Prominent Raman peaks of mixed contaminants were acquired and used to characterize and quantify the pesticides. It was observed that the SERS intensity of the Raman peaks changed in proportion to the concentration ratio of phosmet and paraquat. Moreover, AuNS exhibited superior SERS enhancement compared to gold nanoparticles. The results demonstrate that the lowest detectable concentration for both pesticides on grape surfaces is 0.5mg/kg. These findings suggest that SERS coupled with AuNS constitutes a practical and promising approach for detecting and quantifying trace contaminants in food. PRACTICAL APPLICATION: This research established a novel surface-enhanced Raman spectroscopy (SERS) method coupled with a simplified extraction protocol and gold nanostar substrates to detect trace levels of pesticides in fresh produce. The detection limits meet the maximum residue limits set by the EPA. This substrate has great potential for rapid measurements of chemical contaminants in foods.

Fabrication of polydopamine functionalized AgNF SERS substrate: Applications for sensitive detection of nivalenol in food samples and cell biocompatibility

Surface-enhanced Raman spectroscopy (SERS) is a robust analytical tool applicable for the quick and accurate determination of mycotoxins. However, there hasn't been any attempt to use SERS for the quantitative detection of nivalenol (NIV) thus far. To improve the Raman signals of NIV, we fabricated a polydopamine-coated silver nanoflower (PDA-AgNFs) SERS substrate with strong “hot-spots”. The PDA-AgNFs substrates showed superior SERS enhancement activities in the target analyte detection and quantification. It produced good substrate uniformity (relative standard deviation of SERS signals, RSD = 4.1% for substrate-to-substrate test, and 3.24% for spot-to-spot test), an enhancement factor of 2.87 × 106 towards rhodamine 6B (R6G), and detection sensitivity as low as 1 femtomolar (10−15 M) against R6G probe molecule. Moreover, the PDA-AgNFs SERS substrates were successfully used, for the first time, to detect NIV in corn, horse beans, and mushroom samples. The calibration curve showed a satisfactory linear fit based on the SERS intensities of different NIV concentrations. The detection limit (LOD) for the suggested approach was 0.22 nM (S/N = 3). Interestingly, the MTT assay experiment demonstrated that PDA-AgNFs had no toxicity against mammalian NIH-3T3 cells. The biocompatible PDA-AgNFs substrates with intense plasmonic effects and binding sites demonstrated impressive Raman enhancement, and could serve as an effective, label-free, and fast SERS-based analysis of NIV in real samples.