Polymer multilayers enabled stable and flexible Au@Ag nanoparticle array for nondestructive SERS detection of pesticide residues

A multiplex fluorescent microsphere immunochromatography assay for simultaneous detection of phorate, fenthion, and profenofos

The mass production and use of organophosphorus pesticides (OPs) have led to a threat to human health. Therefore, establishing a sensitive, rapid, and high-throughput detection method is of great importance. In this study, computer-aided molecular design was firstly applied to design the specific haptens of phorate (PHO), fenthion (FEN), and profenofos (PRO), and high-performance monoclonal antibodies against PHO, FEN, and PRO were prepared. On this basis, a multiplex fluorescent microsphere immunochromatographic assay (FM-ICA) was developed for simultaneous detection of three OPs in cowpea and orange samples. The quantitative detection ranges of PHO, FEN, and PRO were 9.039-140.129, 6.686-108.613, and 5.215-71.479 μg/kg, respectively, in cowpeas; and 7.120-121.566, 3.592-92.185, and 3.579-60.081 μg/kg, respectively, in oranges. The results of recovery and real sample testing showed that the multiplex FM-ICA was rapid and accurate, making it suitable for the on-site testing of a large number of samples.

SERS-based simplified analysis of paraquat in poisoning cases: Bypassing complicated pretreatment with antioxidant sensor

Applying antioxidant coating materials to prepare surface-enhanced Raman spectroscopy (SERS) sensing substrates can effectively enhance the sensitivity and stability for the analysis of molecules. In this study, we have leveraged SERS to develop an innovative sensor for the swift identification of Paraquat (PQ), enabling on-site detection of this herbicide. The newly devised sensor distinguishes itself through its exceptional oxidation resistance. This resistance is attributed to the physical properties of the nanoparticles, specifically the silver shell coating and loading on the molybdenum disulfide (MoS2). By the creation of "hot spots" of the composite nanoparticles (Ag@AuBPs on flower-like MoS2), the kit achieves a remarkably low detection limit as low as 1.0 × 10-10 M for Paraquat in lake water, soil, and clothing samples, allowing for rapid and direct identification of PQ in complex environments.

Fabrication of Silicon Surface Microstructures via Vortex Femtosecond Laser Irradiation for Reusable Substrates in SERS Applications

Surface-enhanced Raman spectroscopy (SERS) is a key technique in analytical chemistry because of its exceptional sensitivity and specificity for detecting a broad spectrum of substances. Herein, a silicon (Si) substrate fabricated using vortex femtosecond laser beams in ambient air is proposed as an innovative, highly sensitive, and reusable platform for advanced SERS applications. The substrate has composite nanostructures adorned with bush-like formations on top of the elongated structures, which is a direct consequence of the orbital angular momentum of the vortex beam. Simulations conducted using COMSOL provide valuable insights into the distribution of hot spots and electromagnetic field across the substrate surface after gold nanoparticles deposition, underscoring the superior SERS detection capabilities of the fabricated substrate using vortex beams as compared to those processed by Gaussian beams. The vortex-fabricated substrate possesses remarkable reusability, stability, and time-resistance. It exhibited outstanding detection performance for malachite green and microcystin-LR, achieving limits of detection values of 3.91 pM and 2.69 pg·mL-1, respectively. Therefore, the Si substrates fabricated using a vortex femtosecond laser beam is an ideal candidate for advancing SERS sensors to new heights.

Flexible label-free SERS substrate with alginate-chitosan@silver nanocube for in situ nondestructive detection of thiram on apples

The rapid in situ detection of pesticide residues in real samples based on surface-enhanced Raman spectroscopy (SERS) remains a challenge, necessitating an urgent need for a feasible solution that addresses issues such as sample complexity, reproducibility, and SERS substrate stability. This paper proposes a flexible SERS substrate, which consists of a composite gel made of sodium alginate-chitosan loaded with silver nanocubes (SA-CTS@AgNCs). The flexible nature of the SERS substrate enables the analysis of irregular surfaces of apples, dispensing with laborious pretreatment and promoting an effective contact with target molecules. By utilizing the SA-CTS@AgNCs substrate in conjunction with a portable Raman instrument, an exceptional sensitivity was achieved with a detection limit of 0.055 mg/L for thiram in apples. In addition, the stability, homogeneity, and batch-to-batch reproducibility of the substrates were evaluated. The experimental results showed that after 45 days of storage, the substrate still maintained more than 84.40 % SERS activity, demonstrating long-term stability. Within a single substrate, the point-to-point relative standard deviation (RSD) was only 4.2 %, while among different batches of substrates, the RSD was as low as 6.8 %, displaying better homogeneity and reproducibility. Hence, this flexible SERS substrate provides a reliable and convenient platform for rapid detection and on-site monitoring of food safety.

Selective and sensitive detection of dimethyl phthalate in water using ferromagnetic nanomaterial-based molecularly imprinted polymers and SERS

To overcome the complicated pretreatment, low selectivity and low sensitivity detection associated with the detection of dimethyl phthalate (DMP), this study synthesized ferromagnetic nanomaterials that coupled with surface enhanced Raman scattering (SERS) and molecular imprinting polymers (MIPs). The pretreatment process can be simplified by ferromagnetic nanomaterials, then Fe3O4@SiO2@Ag@MIPs selectively adsorbing DMP can be achieved, and SERS can be applied for DMP detection with high sensitivity. As a control, the non-imprinted polymers (NIPs) Fe3O4@SiO2@Ag@NIPs were synthesized. Adsorption experiments results showed that the saturation adsorption amounts of Fe3O4@SiO2@Ag@MIPs is 36.74 mg/g with 40 mg/L DMP and Fe3O4@SiO2@Ag@NIPs is 17.45 mg/g. For DMP, Fe3O4@SiO2@Ag@MIPs have a greater affinity. In addition, after seven adsorption-desorption cycles the Fe3O4@SiO2@Ag@MIPs are reusable with approximately a 9.8 % loss in adsorption capacity. With an 8.7 × 10-9 M detection limit, DMP detection was performed by SERS, which revealed that the Raman intensities of the associated characteristic peak were linearly proportional to the DMP concentrations. As a result, the recovery rate of the testing artificial water varied from 87.9 % to 117 %. These outcomes show that the suggested technique for finding DMP in actual water samples is practical.

Elevating electron transfer of recyclable SERS sensor using AuNPs/TiO2/Ti3C2 heterostructures for detection of malachite green in sunfish

Malachite green (MG)-contaminated aquatic products pose a serious threat to animal and human health. Hence, a novel recyclable surface-enhanced Raman scattering (SERS) substrate based on AuNPs/TiO2/Ti3C2 heterostructures was developed for the detection and degradation of MG in aquatic products. Specifically, AuNPs/TiO2/Ti3C2 heterostructures were synthesized by in situ oxidation and electrostatic adsorption based on Ti3C2 nanosheets. The excellent photocatalytic and SERS performance of the AuNPs/TiO2/Ti3C2 was demonstrated by Density functional theory (DFT) calculations and experimental results, which was attributed to the enhancement of charge transfer (CT) after the formation of heterostructures. The results demonstrate that AuNPs/TiO2/Ti3C2 is highly sensitive and recyclable. The detection limit of the sensor for MG is 8.91 × 10-5 mg/L. The sensor can be recycled for five times under the condition of light, and shows satisfactory self-cleaning performance in the food matrix, providing a possible alternative solution for the recyclable detection of MG.

Leveraging generative neural networks for accurate, diverse, and robust nanoparticle design

Tandem neural networks for inverse design can only make single predictions, which limits the diversity of predicted structures. Here, we use conditional variational autoencoder (cVAE) for the inverse design of core-shell nanoparticles. cVAE is a type of generative neural network that generates multiple valid solutions for the same input condition. We generate a dataset from Mie theory simulations, including ten commonly used materials in plasmonic core-shell nanoparticle synthesis. We compare the performance of cVAE with that of the tandem model. Our cVAE model shows higher accuracy with a lower mean absolute error (MAE) of 0.013 compared to 0.046 for the tandem model. Robustness analysis with 100 test spectra confirms the improved reliability and diversity of cVAE. To validate the effectiveness of the cVAE model, we synthesize Au@Ag core-shell nanoparticles. cVAE model offers high accuracy in predicting material composition and spectral features. Our study shows the potential of cVAEs as generative neural networks in producing accurate, diverse, and robust nanoparticle designs.

Facile fabrication of Au-Ag alloy nanoparticles/Ag nanowires SERS substrates with bimetallic synergistic effect for ultra-sensitive detection of crystal violet and alkali blue 6B

The bimetallic nanostructure of Au and Ag can integrate two distinct properties into a novel substrate compared to single metal nanostructures. This work presents a rapid and sensitive surface-enhanced Raman scattering (SERS) substrate for detecting illegal food additives and dyes of crystal violet (CV) and alkali blue 6B (AB 6B). Au-Ag alloy nanoparticles/Ag nanowires (Au-Ag ANPs/Ag NWs) were prepared by solid-state ionics method and vacuum thermal evaporation method at 5μA direct current electric field (DCEF), the molar ratio of Au to Ag was 1:18.34. Many 40 nm-140 nm nanoparticles regularly existed on the surface of Ag NWs with the diameters from 80 nm to 150 nm. The fractal dimension of Au-Ag ANPs/Ag NWs is 1.69 due to macroscopic dendritic structures. Compared with single Ag NWs, the prepared Au-Ag ANPs/Ag NWs substrates show superior SERS performance because of higher surface roughness, the SERS active of Ag NWs and bimetallic synergistic effect caused by Au-Ag ANPs, so the limit of detections (LOD) of Au-Ag ANPs/Ag NWs SERS substrates toward detection of CV and AB 6B were as low as 10-16mol/L and 10-9mol/L, respectively. These results indicate that Au-Ag ANPs/Ag NWs substrates can be used for rapid and sensitive detection of CV and AB 6B and have great development potential for detection of illegal food additives and hazardous substances in the fields of environmental monitoring and food safety.

Non-invasive detection of systemic lupus erythematosus using SERS serum detection technology and deep learning algorithms

Systemic lupus erythematosus (SLE) is an autoimmune disease with multiple symptoms, and its rapid screening is the research focus of surface-enhanced Raman scattering (SERS) technology. In this study, gold@silver-porous silicon (Au@Ag-PSi) composite substrates were synthesized by electrochemical etching and in-situ reduction methods, which showed excellent sensitivity and accuracy in the detection of rhodamine 6G (R6G) and serum from SLE patients. SERS technology was combined with deep learning algorithms to model serum features using selected CNN, AlexNet, and RF models. 92 % accuracy was achieved in classifying SLE patients by CNN models, and the reliability of these models in accurately identifying sera was verified by ROC curve analysis. This study highlights the great potential of Au@Ag-PSi substrate in SERS detection and introduces a novel deep learning approach for SERS for accurate screening of SLE. The proposed method and composite substrate provide significant value for rapid, accurate, and noninvasive SLE screening and provide insights into SERS-based diagnostic techniques.

Surface-enhanced Raman scattering based on noble metal nanoassemblies for detecting harmful substances in food

Residues of harmful substances in food can severely damage human health. The content of these substances in food is generally low, making detection difficult. Surface-enhanced Raman scattering (SERS), based on noble metal nanomaterials, mainly gold (Au) and silver (Ag), has exhibited excellent capabilities for trace detection of various substances. Noble metal nanoassemblies, in particular, have extraordinary flexibility and tunable optical properties, which cannot be offered by single nanoparticles (NPs). These nanoassemblies, with their various morphologies synthesized using NPs through artificially induced self-assembly or template-driven preparation, can significantly enhance the local electric field and create "hot spots" due to the gaps between adjacent NPs. Consequently, the SERS properties of NPs become more prominent, leading to improved performance in the trace detection of various substances and detection limits that are considerably lower than the current relevant standards. Noble metal nanoassemblies show promising potential in ensuring food safety. This review discusses the synthesis methods and SERS properties of noble metal nanoassemblies and then concentrates on their application in detecting biotoxins, drug residues, illegal additives, and heavy metals. The study provides valuable references for further research into the application of nanoassemblies in food safety detection.

Mo-doped Co LDHs as Raman enhanced substrate for detection of roxarsine

BACKGROUND

Roxarsone (ROX) is widely used as a feed additive, which is indigestible after ingestion by poultry, and most of it can only be excreted into the natural environment and degraded into highly toxic and carcinogenic inorganic arsenic compounds, which pose a hazard to the ecosystem and human health. However, for roxarsone, traditional detection methods require complex and time-consuming procedures, so it is urgent to find a new fast detection method for detection of ROX.

RESULTS

In this work, we developed a novel Raman enhancement material and utilized the Surface-enhanced Raman scattering (SERS) technique to achieve rapid and sensitive detection of roxarsone. Specifically, Mo-doped cobalt layered double hydroxides (Co-LDHs) semiconductor material (abbreviated as CMM-100) was prepared by a simple method of using ion-assisted MOF etching. Under laser excitation at a wavelength of 532 nm, the CMM-100 showed excellent SERS property to various organic dye molecules such as methylene blue (MB), Toluidine Blue(TB), and Crystal Violet (CV). Especially, an enhancement factor (EF) of 1.4 × 106 was achieved for MB. Compared with the traditional method, this work utilized the fast and non-destructive SERS technology, which achieved a rapid detection of ROX. The detection limit was as low as 9.73 × 10-10 M, and the detection range was from 10-9 M to 10-3 M.

SIGNIFICANCE

In this work, SERS technology was adopted for the rapid and sensitive detection of ROX. This study provides a Raman-enhanced substrate named CMMs for detection of food additives, pesticides, biomolecules, etc., which also broadens the application areas of SERS materials.

A self-calibrating flexible SERS substrate incorporating PB@Au assemblies for reliable and reproducible detection

The precise quantitative analysis using surface-enhanced Raman spectroscopy (SERS) in an uncontrollable environment still faces a significant obstacle due to the poor reproducibility of Raman signals. Herein, we propose a facile method to fabricate a self-calibrating substrate based on a flexible polyvinyl alcohol (PVA) film comprising assemblies of Prussian blue (PB) and Au NPs (PB@Au) for reliable detection. PB cores were coated with an Au shell through simple electrostatic interaction, forming core-shell nanostructure PB@Au assemblies within the PVA film. The outer Au layer provided identical trends in enhancement for both the PB core and neighboring targets while PB cores served as an internal standard (IS) to correct signal fluctuations. The prevention of competitive adsorption on the metal surface between targets and ISs was achieved. The proposed PVA/PB@Au film exhibited enhanced stability of Raman signals after IS correction, resulting in improved spot-to-spot and batch-to-batch reproducibility with significantly reduced standard deviation (RSD) values from 11.42% and 25.02% to 4.43% and 9.39%, respectively. Simultaneously, a higher accuracy in the quantitative analysis of 4-mercaptobenzoic acid (4-MBA) and malachite green (MG) was achieved with fitting coefficient (R2) values improving from 0.9675 and 0.9418 to 0.9974 and 0.9832, respectively. Moreover, the PVA/PB@Au film was successfully applied to detect residual MG in real fish samples. This work opens up an avenue to improve the reproducibility of Raman signals for flexible SERS substrates in the detection of residues under various complex conditions.

Developing a magnetic SERS nanosensor utilizing aminated Fe-Based MOF for ultrasensitive trace detection of organophosphorus pesticides in apple juice

The unreasonable use of organophosphorus pesticides leads to excessive pesticide residues in food, seriously threatening public health, and the potential of surface-enhanced Raman spectroscopy (SERS) technology, incorporating a metal-organic framework, is substantial for the rapid detection of trace pesticide residues. Here, a novel Fe3O4@NH2-MIL-101(Fe)@Ag (FNMA) SERS nanosensor was developed. Results indicated that the FNMA had a high enhancement factor of 1.53 × 108, a low limit of detection (LOD) of 4.55 × 10-12 M, and a relative standard deviation of 7.73 % for 4-nitrothiophenol, demonstrating its good SERS sensitivity and uniformity, and also possessed good storage stability for one month. In quantifying fenthion and methyl parathion in standard solutions and apple juice in the range of 0.05/0.02-20 mg/L, it showed LODs of 3.02 × 10-3 mg/L and 1.43 × 10-3 mg/L, and 0.0407 and 0.0075 mg/L, respectively, demonstrating potentials in ultrasensitive trace detection of pesticides in food.

Recent developments and applications of surface enhanced Raman scattering spectroscopy in safety detection of fruits and vegetables

This article reviewed the latest research progress of Surface-enhanced Raman Spectroscopy (SERS) in the security detection of fruits and vegetables in recent years, especially in three aspects: pesticide residues, microbial toxin contamination and harmful microorganism infection. The binding mechanism and application potential of SERS detection materials (including universal type and special type) and carrier materials (namely rigid and flexible materials) were discussed. Finally, the application prospect of SERS in fruit and vegetable safety detection was explored, and the problems to be solved and development trends were put forward. The poor stability and reproducibility of SERS substrates make it difficult for practical applications. It is necessary to continuously optimize SERS substrates and develop small and portable Raman spectroscopy analyzers. In the future, SERS technology is expected to play an important role in human health, food safety and economy.

Research Status in the Use of Surface-Enhanced Raman Scattering (SERS) to Detect Pesticide Residues in Foods and Plant-Derived Chinese Herbal Medicines

Surface-enhanced Raman scattering (SERS) technology has unique advantages in the rapid detection of pesticides in plant-derived foods, leading to reduced detection limits and increased accuracy. Plant-derived Chinese herbal medicines have similar sources to plant-derived foods; however, due to the rough surfaces and complex compositions of herbal medicines, the detection of pesticide residues in this context continues to rely heavily on traditional methods, which are time consuming and laborious and are unable to meet market demands for portability. The application of flexible nanomaterials and SERS technology in this realm would allow rapid and accurate detection in a portable format. Therefore, in this review, we summarize the underlying principles and characteristics of SERS technology, with particular focus on applications of SERS for the analysis of pesticide residues in agricultural products. This paper summarizes recent research progress in the field from three main directions: sample pretreatment, SERS substrates, and data processing. The prospects and limitations of SERS technology are also discussed, in order to provide theoretical support for rapid detection of pesticide residues in Chinese herbal medicines.

Developments in food neonicotinoids detection: novel recognition strategies, advanced chemical sensing techniques, and recent applications

Neonicotinoid insecticides (NEOs) are a new class of neurotoxic pesticides primarily used for pest control on fruits and vegetables, cereals, and other crops after organophosphorus pesticides (OPPs), carbamate pesticides (CBPs), and pyrethroid pesticides. However, chronic abuse and illegal use have led to the contamination of food and water sources as well as damage to ecological and environmental systems. Long-term exposure to NEOs may pose potential risks to animals (especially bees) and even human health. Consequently, it is necessary to develop effective, robust, and rapid methods for NEOs detection. Specific recognition-based chemical sensing has been regarded as one of the most promising detection tools for NEOs due to their excellent selectivity, sensitivity, and robust interference resistance. In this review, we introduce the novel recognition strategies-enabled chemical sensing in food neonicotinoids detection in the past years (2017-2023). The properties and advantages of molecular imprinting recognition (MIR), host-guest recognition (HGR), electron-catalyzed recognition (ECR), immune recognition (IR), aptamer recognition (AR), and enzyme inhibition recognition (EIR) in the development of NEOs sensing platforms are discussed in detail. Recent applications of chemical sensing platforms in various food products, including fruits and vegetables, cereals, teas, honey, aquatic products, and others are highlighted. In addition, the future trends of applying chemical sensing with specific recognition strategies for NEOs analysis are discussed.

Ag microlabyrinth/nanoparticles coated large-area thin PDMS films as flexible and transparent SERS substrates for in situ detection

Flexible and transparent surface-enhanced Raman scattering (SERS) substrates haveattractedmuchattention as a fast, sensitive and in situ detection platform for practical applications. However, the large-area fabrication of flexible and transparent SERS substrates with high performance is still challenging. Here, a flexible and transparent SERS substrate based on large-area thin PDMS film decorated with Ag microlabyrinth/nanoparticles hierarchical structures (denoted as ALNHS@PDMS) is fabricated by using the floating-on-water method and magnetron sputtering technology. By optimizing the sputtering time, the ALNHS with multiple hot spots are uniformly distributed on the PDMS surface. Based on characterizing the rhodamine 6G (R6G) with a portable Raman spectrometer, the optimal ALNHS@PDMS film exhibits a high enhancement factor (5.2 × 106), excellent uniformity and reproducibility, as well as superior mechanical stability. In addition, thanks to the good sticky feature and bi-directional activation property of the thin ALNHS@PDMS film, the prepared flexible and transparent SERS substrate can achieve in situ detection of malachite green residues (10-6 M) on apple and tomato skins. This large-area, thin, mechanically robust, flexible and transparent ALNHS@PDMS film, integrated with a portable Raman spectrometer, shows great potential for point-of-care testing (POCT)in practical applications.

SERS immunoassay analysis of Escherichia coli and Staphylococcus aureus based on sandwich-structured complex probe and target-induced strand displacement

A direct and ultra-sensitive surface-enhanced Raman scattering (SERS) immunoassay method is introduced for the detection of Escherichia coli and Staphylococcus aureus. This methodology is based on a sandwich-structured complex probe (SCP) mechanism, combined with target-induced strand displacement. Moreover, by leveraging the amplified SERS signal from gold nanoparticles (AuNPs) corresponding to an increase in bacterial count, we achieve quantitative determination. The SCP demonstrates remarkable specificity, sensitivity, and anti-interference capability in bacterial detection. The detection limits for both bacterial strains are as low as 10 CFU/mL. In our selectivity tests, all peak intensities had standard deviations (n = 3) below 6%. Recoveries in normal human serum were 101-110% for E. coli and 96-101% for S. aureus. In milk, the recoveries were 102-105% for E. coli and 100-105% for S. aureus, respectively, demonstrating a high level of accuracy and resistance to interference. In addition, the SCP offers a dual-detection capability, enabling simultaneous diagnosis of multiple targets, which greatly simplifies the testing procedure. The findings underscore that this immunoassay platform fulfills the demand for rapid and precise pathogenic bacterial diagnosis, holding substantial potential for practical applications.

Self-assembly flexible SERS imprinted membrane based on Ag nanocubes for selective detection of microcystin-LR

Silver nanocubes monolayer-modified polydimethylsiloxane (Ag NC/PDMS) flexible SERS substrates have been prepared by a three-phase interface self-assembly procedure. The combination of this method with membrane technology brings nanoparticles in close proximity, densely, and regularly arranged in monolayers over a large area, leading to excellent SERS properties. Considering the complexity of practical detection, molecular imprinted polymers (MIPs) were anchored on the surface of SERS substrate and applied to selective detection of microcystin-LR (MC-LR). It is worth mentioning that the SERS imprinted membranes (AP-MIMs) were still clearly detected at a concentration of 0.1 µg·L-1 of MC-LR in drinking water, and the detection limit was as low as 0.0067 µg·L-1. The substrate exhibited excellent uniformity with a relative standard deviation (RSD) of 6.1%. In the presence of interference molecules, AP-MIMs exhibited excellent selectivity for MC-LR. Furthermore, in the spiking and recovery tests of practical lake water samples, the method showed excellent recoveries ranging from 96.47 to 105.31%. It has been demonstrated that the prepared AP-MIMs can be applied to sensitive and specific detection of trace amounts of MC-LR in drinking water.

Modified paper-based substrates fabricated via electrostatic attraction of gold nanospheres for non-destructive detection of pesticides based on surface-enhanced Raman spectroscopy

BACKGROUND

Flexible surface-enhanced Raman spectroscopy (SERS) substrates such as paper-based substrates show great potential for rapid detection of residual chemicals on food surfaces. However, controlling the density and distribution of metallic nanoparticles adsorbed on the paper is still challenging.

RESULTS

The amount of gold (Au) nanospheres (51 ± 4 nm) attached on the filter paper modified with 3-aminopropyltriethoxysilane (APTES) was tunable, increasing as the level of APTES (2.5-15.0 g kg-1 ) applied for paper modification increased. Moreover, the Au nanospheres were relative evenly distributed on the filter paper modified with 2.5-10.0 g kg-1 of APTES, which resulted in excellent intra- and inter-reproducibility of SERS signals for pesticides including thiram, diquat dibromide, and paraquat dichloride (relative standard deviation = 2.2-10.1%). The modified paper-based substrate could be used to detect as low as 0.05-0.2 mg L-1 of pesticides in standard solutions, and as low as 5-20 ng cm-2 of residual pesticides on apple skins with minimum sample pretreatment.

CONCLUSION

This paper-based substrate with tunable feature for the density and distribution of nanoparticles is applicable for rapid SERS detection of residual pesticides in fruits and vegetables. © 2023 Society of Chemical Industry.

A SERS Composite Hydrogel Device for Point-of-Care Analysis of Neurotransmitter in Whole Blood

Point-of-care analysis of neurotransmitters in body fluids plays a significant role in healthcare improvement. Conventional approaches are limited by time-consuming procedures and usually require laboratory instruments for sample preparation. Herein, we developed a surface enhanced Raman spectroscopy (SERS) composite hydrogel device for the rapid analysis of neurotransmitters in whole blood samples. The PEGDA/SA composite hydrogel enabled fast separation of small molecules from the complex blood matrix, while the plasmonic SERS substrate allowed for the sensitive detection of target molecules. 3D printing was employed to integrate the hydrogel membrane and the SERS substrate into a systematic device. The sensor achieved highly sensitive detection of dopamine in whole blood samples with a limit of detection down to 1 nM. The whole detection process from sample preparation to SERS readout can be finished within 5 min. Due to the simple operation and rapid response, the device shows great potential in point-of-care diagnosis and the monitoring of neurological and cardiovascular diseases and disorders.

Preparation of size-controlled LiCoPO4 particles by membrane emulsification using anodic porous alumina and their application as cathode active materials for Li-ion secondary batteries

Membrane emulsification using anodic porous alumina is an effective method for preparing monodisperse droplets with controlled sizes. In this study, membrane emulsification using anodic porous alumina was applied to the preparation of size-controlled particles composed of composite metal oxides. To obtain size-controlled composite metal oxide particles, membrane emulsification was performed using an aqueous solution containing a water-soluble monomer and metal salts as a dispersed phase. After the membrane emulsification, composite metal oxide particles were obtained by solidifying the droplets in a continuous phase and subsequent heat treatment. Here, as a demonstration of this process, the fabrication of size-controlled LiCoPO4 particles, which are considered high-potential cathode active materials for Li-ion secondary batteries (LIBs), was investigated. The application of the obtained LiCoPO4 particles as cathode active materials for LIBs was also investigated. The results of this study showed that LiCoPO4 particles with controlled sizes could be fabricated on the basis of this process and that their cathode properties could be improved by optimizing the heat treatment conditions and particle sizes. According to this process, size-controlled particles composed of various metal oxides can be fabricated by changing the metal salt in the dispersed phase, and the resulting size-controlled particles are expected to be applied not only as cathode active materials for LIBs but also as components of various functional devices.

Deep eutectic solvent-based adhesive tape extraction combined with enzyme inhibition assay for the determination and distinction of dithiocarbamate pesticides in food samples

A simple, green extraction method of dithiocarbamate (DTC) pesticides in food samples was developed using adhesive tapes and a green deep eutectic solvent (DES). A rapid and convenient determination and distinction method of DTC pesticides was established using tyrosinase inhibition assay. First, DTC pesticides were extracted by pasting and peeling off the adhesive tape, then eluted by the DES synthesized from xylitol and ethylene glycol. Second, determination of DTC pesticides was conducted by inhibiting the activity of tyrosinase which can catalyze the oxidation of catechol. Less colored products were generated in the reaction system (tyrosinase, catechol, and 4-aminoantipyrine), leading to weak absorbance. In addition, different DTC pesticides (ziram, propineb, zineb, mancozeb, thiram, metiram, and ferbam) were successfully distinguished by sensor arrays (tyrosinase, phenolic compounds, and 4-aminoantipyrine) through principal component analysis. The limit of detection was found to be 0.2 μg kg^-1, and the limit of quantification was 0.6 μg kg^-1. The recoveries ranging from 89.4% to 103.8% were obtained in vegetable, fruit, and cereal, with a relative standard deviation of less than 4.2%. The method is simple, rapid, and convenient and shows good application prospects in the determination of pesticides in a variety of food samples.

Raman spectroscopy in crop quality assessment: focusing on sensing secondary metabolites: a review

As a crop quality sensor, Raman spectroscopy has been consistently proposed as one of the most promising and non-destructive methods for qualitative and quantitative analysis of plant substances, because it can measure molecular structures in a short time without requiring pretreatment along with simple usage. The sensitivity of the Raman spectrum to target chemicals depends largely on the wavelength, intensity of the laser power, and exposure time. Especially for plant samples, it is very likely that the peak of the target material is covered by strong fluorescence effects. Therefore, methods using lasers with low energy causing less fluorescence, such as 785 nm or near-infrared, are vigorously discussed. Furthermore, advanced techniques for obtaining more sensitive and clear spectra, like surface-enhanced Raman spectroscopy, time-gated Raman spectroscopy or combination with thin-layer chromatography, are being investigated. Numerous interpretations of plant quality can be represented not only by the measurement conditions but also by the spectral analysis methods. Up to date, there have been attempted to optimize and generalize analysis methods. This review summarizes the state of the art of micro-Raman spectroscopy in crop quality assessment focusing on secondary metabolites, from in vitro to in vivo and even in situ, and suggests future research to achieve universal application.

Two-Dimensional Printed AgNPs@Paper Swab for SERS Screening of Pesticide Residues on Apples and Pears

In recent years, growing food safety and quality concerns have emerged and created an urgent need for the development of rapid and reliable food control technologies. This study proposes a novel surface-enhanced Raman spectroscopy (SERS) substrate printing technology that utilizes commercial filter paper functionalized by silver nanoparticles. We modified the Automatic TLC Sampler using a two-dimensional (2D) printer. The modification allows for various sampling modes which can be applied to 2D printing. The shape and size of nano silver on the substrate were determined, and the substrate sensitivity, uniformity, and stability were evaluated. As demonstrated by the experimental outcomes, the proposed technology is highly sensitive and reproducible, that is, the limit of quantitation was 10^-5 mg/kg, and the spot-to-spot and block-to-block Raman intensity variations were below 4.2%. We also successfully applied the technology to pears and apples for thiram recognition, yielding outstanding detectability down to 2.5 × 10^-6 and 3.9 × 10^-7 mg/mL (equal to 2.5 × 10^-3 and 3.9 × 10^-4 mg/kg), respectively. These were well below the maximum residue limit (7 mg/kg). More importantly, the linear relationships between thiram levels and the SERS intensity allow for sensitive monitoring of minute variations in agricultural insecticide residues. This proposed detection method can realize in situ detection with a strong signal fingerprint.

Label-free MIP-SERS biosensor for sensitive detection of colorectal cancer biomarker

Early diagnosis of colorectal cancer can significantly improve the overall survival rate of patients, thus selective and sensitive detection of biomarkers in serum samples is vital for early detection and dynamic monitoring of cancer. Nucleoside diphosphate kinase NM23-H2 (NDKB) is an important biomarker and therapeutic target for the diagnosis of colorectal cancer (CRC). Here, a label-free and ultrasensitive biosensor for NDKB protein markers is presented for the first time, combining the characteristic capture selectivity of molecularly imprinted polymers (MIPs) and the ultrasensitivity of surface-enhanced Raman Spectroscopy (SERS) technique. The imprinted cavity serves as the only channel for Raman reporter to approach the SERS substrate, providing highly complementary non-covalent binding sites that selectively capture the target protein based on ionic, hydrogen bonding or hydrophobic interactions. Specific recognition of the NDKB protein will perfectly fill the imprinted cavity, which makes it difficult for the Raman reporter to get close to the SERS substrate, and the Raman signal decreases significantly, while the proteins of other structural sizes can not match the imprinted cavity. Through the change of the Raman signal, the proposed biosensor can realize the ultra-sensitive detection of NDKB, and the limit of detection (LOD) is 0.82 pg/mL. Compared with the traditional immunoassay technology, this combined approach with the advantages of low cost, fast response, high sensitivity and selectivity, provides clinical application potential for the early diagnosis of CRC.

Advances in surface-enhanced Raman spectroscopy technology for detection of foodborne pathogens

Rapid control and prevention of diseases caused by foodborne pathogens is one of the existing food safety regulatory issues faced by various countries and has received wide attention from all sectors of society. The development of rapid and reliable detection methods for foodborne pathogens remains a hot research area for food safety and public health because of the limitations of complex steps, time-consuming, low sensitivity, or poor selectivity of commonly used methods. Surface-enhanced Raman spectroscopy (SERS), as a novel spectroscopic technique, has the advantages of high sensitivity, selectivity, rapid and nondestructive detection and has exhibited broad application prospects in the determination of pathogenic bacteria. In this study, the enhancement mechanisms of SERS are briefly introduced, then the characteristics and properties of liquid-phase, rigid solid-phase, and flexible solid-phase are categorized. Furthermore, a comprehensive review of the advances in label-free or label-based SERS strategies and SERS-compatible techniques for the detection of foodborne pathogens is provided, and the advantages and disadvantages of these methods are reviewed. Finally, the current challenges of SERS technology applied in practical applications are listed, and the possible development trends of SERS in the field of foodborne pathogens detection in the future are discussed.

Nondestructive testing methods for pesticide residue in food commodities: A review

Pesticides play an important role in increasing the overall yield and productivity of agricultural foods by controlling pests, insects, and numerous plant-related diseases. However, the overuse of pesticides has resulted in pesticide contamination of food products and water bodies, as well as disruption of ecological and environmental systems. Global health authorities have set limits for pesticide residues in individual food products to ensure the availability of safe foods in the supply system and to assist farmers in developing the best agronomic practices for crop production. Therefore, the use of nondestructive testing (NDT) methods for pesticide residue detection is gaining interest in the food supply chain. The NDT techniques have several advantages, such as simultaneous measurement of chemical and physical characteristics of food without destroying the product. Although numerous studies have been conducted on NDT for pesticide residue in agro-food products, there are still challenges in real-time implementation. Further study on NDT methods is needed to establish their potential for supplementing existing methods, identifying mixed pesticides, and performing volumetric quantification (not surface accumulation alone).

Discrimination of Pericarpium Citri Reticulatae in different years using Terahertz Time-Domain spectroscopy combined with convolutional neural network

Pericarpium Citri Reticulatae (PCR) in longer storage years possess higher medicinal values, but their differentiation is difficult due to similar morphological characteristics. Therefore, this study investigated the feasibility of using terahertz time-domain spectroscopy (THz-TDS) combined with a convolutional neural network (CNN) to identify PCR samples stored from 1 to 20 years. The absorption coefficient and refractive index spectra in the range of 0.2-1.5 THz were acquired. Partial least squares discriminant analysis, random forest, least squares support vector machines, and CNN were used to establish discriminant models, showing better performance of the CNN model than the others. In addition, the output data points of the CNN intermediate layer were visualized, illustrating gradual changes in these points from overlapping to clear separation. Overall, THz-TDS combined with CNN models could realize rapid identification of different year PCRs, thus providing an efficient alternative method for PCR quality inspection.

A SERS-Fluorescence dual-signal aptasensor for sensitive and robust determination of AFB1 in nut samples based on Apt-Cy5 and MNP@Ag-PEI

Food aflatoxin B1 (AFB1) contamination greatly threatens human health and its sensitive determination is imperative. In this study, a surface-enhanced Raman scattering (SERS) and fluorescence dual-signal aptasensor was constructed for sensitive AFB1 detection in peanuts, walnuts, and almonds samples. Fluorescent dye cy5 was used as fluorophore and Raman reporter, while polyethyleneimine modified Ag coating magnetic nanoparticles (MNP@Ag-PEI) were utilized to absorb the cy5 modified aptamer (apt-cy5). Results indicated that linear ranges of 0.001-1000 ng/mL and 0.2-20,000 ng/mL with detection limits of 0.45 pg/mL and 0.135 ng/mL for the SERS and fluorescence methods were obtained, respectively, and AFB1 detection in the nut samples using the aptasensor achieved satisfactory recoveries of 95.2%-108.6% for SERS and 94.7%-109.7% for fluorescence. Compared with other mono signal detection, the established aptasensor facilely fused the merits of the two signals and improved the detection accuracy and flexibility.

Functional Micro-/Nanostructures in Agrofood Science: Precise Inspection, Hazard Elimination, and Potential Health Risks

Nanotechnology, biotechniques, and chemical engineering have arisen as new trends with significant impacts on agrofood science development. Advanced analytical techniques with high sensitivity, specificity, and automation based on micro-/nanomaterials for food hazard elimination have become leading research hotspots in agrofood science. Research progress in micro-/nanomaterials has provided a solid theoretical basis and technical support to solve problems in the industry. However, the rapid development of micro-/nanostructures has also raised concerns regarding potential risks to human health. This review presents the latest advances in the precise inspection and elimination of food hazards from micro-/nanomaterials and discusses the potential threats to human health posed by nanomaterials. The theoretical reference was provided for the application trend of micro-/nanomaterials in the field of agrofood science in the future.

Analysis and detection using novel terahertz spectroscopy technique in dietary carbohydrate-related research: Principles and application advances

As one of the main functional substances, carbohydrates account for a large proportion of the human diet. Conventional analysis and detection methods of dietary carbohydrates and related products are destructive, time-consuming, and labor-intensive. In order to improve the efficiency of measurement and ensure food nutrition and consumer health, rapid and nondestructive quality evaluation techniques are needed. In recent years, terahertz (THz) spectroscopy, as a novel detection technology with dual characteristics of microwave and infrared, has shown great potential in dietary carbohydrate analysis. The current review aims to provide an up-to-date overview of research advances in using the THz spectroscopy technique in analysis and detection applications related to dietary carbohydrates. In the review, the principles of the THz spectroscopy technique are introduced. Advances in THz spectroscopy for quantitative and qualitative analysis and detection in dietary carbohydrate-related research studies from 2013 to 2022 are discussed, which include analysis of carbohydrate concentrations in liquid and powdery foods, detection of foreign body and chemical residues in carbohydrate food products, authentication of natural carbohydrate produce, monitoring of the fermentation process in carbohydrate food production and examination of crystallinity in carbohydrate polymers. In addition, applications in dietary carbohydrate-related detection research using other spectroscopic techniques are also briefed for comparison, and future development trends of THz spectroscopy in this field are finally highlighted.

SERS detection of thiram using polyacrylamide hydrogel-enclosed gold nanoparticle aggregates

The development of sensitive and long-term signal-stable plasmonic substrates is vital to the in-field application of the surface-enhanced Raman spectroscopy (SERS) technique. The colloidal gold nanoparticles (AuNPs) system is commonly used in SERS detection, but it shows less signal stability and reproducibility due to the uncontrollable aggregation of nanoparticles by adding aggregating agents in SERS detection. In this study, we developed a new SERS detection platform based on polyacrylamide hydrogel-enclosed plasmonic gold nanoparticle aggregates (PAH-AuANs). In the system, the formation of PAH can rapidly stabilize the gold nanoparticle aggregates, avoiding the over-aggregation or precipitation of AuNPs. With the PAH concentration in the range of 6-10 % and AuNPs at the concentration of 0.2 nM, the resulting PAH-AuNAs platform exhibited both sensitive SERS activity and excellent SERS signal stability. The relative standard deviation of the 4-MBA probe SERS signal collected from the PAH-AuNAs platform was lower than 3 %. The limit of detection for the pesticide thiram was down to 0.38 μg/L with a handheld Raman spectrometer. Moreover, the procedure for preparing the PAH-AuNAs platform was easy to handle, offering a new strategy for in-field detection of environmental contaminants with a handheld Raman spectrometer in the future.

Synthesis of recyclable SERS platform based on MoS2@TiO2@Au heterojunction for photodegradation and identification of fungicides

Surface-enhanced Raman spectroscopy (SERS) substrates based on metal/semiconductors have attracted much attention due to their excellent photocatalytic activity and SERS performance. However, they generally exhibit low light utilization and photocatalytic efficiencies. Herein, molybdenum disulfide coated titanium dioxide modified with gold nanoparticles (MoS₂@TiO₂@Au) as a heterojunction-based recyclable SERS platform was fabricated for the efficient determination of fungicides. Results showed that the MoS₂@TiO₂@Au platform could rapidly degrade 90.7% crystal violet in 120 min under solar light irradiation and enable reproducible and sensitive SERS analysis of three fungicides (methylene blue, malachite green, and crystal violet) and in-situ monitor of the photodegradation process. The platform could also be reused five times due to the unique integrated merits of the MoS₂@TiO₂@Au heterojunction. Meanwhile, experiments in determining methylene blue in prawn protein solution achieved a limit of detection of 1.509 μg/L. Therefore, it is hoped that this work could expand detection applications of photocatalytic materials.

A portable architectonics of Al/carbon nitride/metal-organic frameworks anchored Ag nanoparticles for SERS detection and photocatalytic degradation of fungicide

In recent years, it is urgent to develop bi-functional materials for highly sensitive SERS detection and photocatalytic degradation of contaminants in water of fish pond. Herein, using 5-mercapto-1-methyltetrazole as the ligand, the tree-trunk like zeolitic imidazolate framework (ZIF-8) is induced and in-situ grown on the surface of aluminum/flower carbon nitride (Al/f-C₃N₄). Then, AgNPs are tightly anchored in ZIF-8 of Al/f-C₃N₄/ZIF-8 by strong Ag-N and Ag-S bonds, and a portable architecture of Al/f-C₃N₄/ZIF-8/Ag is successfully prepared. Results indicate that the Al/f-C₃N₄/ZIF-8/Ag architecture exhibits excellent SERS activity and the detection limit can as low as 2.15 × 10^-11 mol⋅L^-1 for crystal violet (CV, a typical fungicide). Also, the Al/f-C₃N₄/ZIF-8/Ag substrate presents good photocatalytic activity for CV molecule, and the degradation efficiency reaches 98.58% after illumination for 90 min. This is mainly due to the good adsorption capacity of ZIF-8 which can enrich more CV molecules and pull them to "hot spots" generated by Ag in Al/f-C₃N₄/ZIF-8/Ag, and thus SERS response are enhanced significantly. Besides, the strong synergistic effect of f-C₃N₄, ZIF-8 and AgNPs is also important which facilitates the separation of photogenerated electrons and holes. Thus, the designed portable and bi-functional substrate could be used as a potential material for the detection and removal of CV in practical application.

Mesoporous silica coated core-shell nanoparticles substrate for size-selective SERS detection of chloramphenicol

With the growing popularity of the non-destructive technique, surface-enhanced Raman spectroscopy (SERS) demands a highly sensitive and reproducible plasmonic nanoparticles substrate. In this study, a novel bimetallic core-shell nanoparticles (Au@Ag@mSiO₂NP) substrate consisting of a gold core, silver shell, and a mesoporous silica coating was synthesized. The mesoporous coating structure was created by employing template molecules such as surfactant and their subsequent removal allowing selective screening based on the size of analyte molecules. Results showed that the plasmonic substrate could selectively enhance small molecules by preventing large macromolecules to reach the exciting zone of the substrate core, achieving the detection of chloramphenicol in milk samples with a detection limit of 6.68 × 10^-8 M. Moreover, the mesoporous coating provided additional stability to the Au@Ag nanoparticles, leading to the reusability of the substrate. Thus, this work offered a simple and smart Au@Ag@mSiO₂NP substrate for effective SERS detection of analytes.

Diffusive Formation of Au/Ag Alloy Nanoparticles of Governed Composition in Glass

For the first time we show that the introduction of silver ions in the glass containing gold nanoparticles (NPs) and additional heat treatment of the glass in the air lead to the formation of Au/Ag alloy NPs. The proposed approach makes it possible to position localized surface plasmon resonance of the NPs by selecting the heat treatment temperature, which determines the silver proportion in the alloy NPs. This allows for expanding customizability of NPs for applications in surface-enhanced Raman scattering spectroscopy, catalysis and biochemistry. Developed technique benefits from the presence of silver in the glass in ionic form, which prevents the oxidation of silver and provides stable preparation of Au/Ag alloy NPs.

Ultra-trace and quantitative SERS detection of polycyclic aromatic hydrocarbons based on Au nanoscale convex polyhedrons with embedded probe molecules

Surface-enhanced Raman scattering (SERS) has great potential for the detection of marine pollutants, but it is still restricted in ultra-trace and quantitative analysis. Here, a strategy for the detection of polycyclic aromatic hydrocarbons (PAHs) was proposed based on Au nanoscale convex polyhedrons (Au NCPs) coated with high-energy facets and embedded with 4-ATP as a probe molecule. Au NCPs acted as SERS substrates and led to limits of detection (LODs) for six common PAHs that reached 0.01 nM. Using internal calibration, the relative standard deviations (RSD) of the spectral stability and reproducibility were as low as 3.36% and 5.11%, respectively. The maximum mean relative errors (AREs) of the predicted and true values were 6.28%. The results indicate that the resulting Au NCPs improved the ultra-trace and quantitative detection of SERS, thus suggesting that the Au NCPs have practical application value in SERS.

Quantitative Analysis of Acetone in Transformer Oil Based on ZnO NPs@Ag NWs SERS Substrates Combined with a Stoichiometric Model

Acetone is an essential indicator for determining the aging of transformer insulation. Rapid, sensitive, and accurate quantification of acetone in transformer oil is highly significant in assessing the aging of oil-paper insulation systems. In this study, silver nanowires modified with small zinc oxide nanoparticles (ZnO NPs@Ag NWs) were excellent surface-enhanced Raman scattering (SERS) substrates and efficiently and sensitively detected acetone in transformer oil. Stoichiometric models such as multiple linear regression (MLR) models and partial least square regressions (PLS) were investigated to quantify acetone in transformer oil and compared with commonly used univariate linear regressions (ULR). PLS combined with a preprocessing algorithm provided the best prediction model, with a correlation coefficient of 0.998251 for the calibration set, 0.997678 for the predictive set, a root mean square error in the calibration set (RMSECV = 0.12596 mg/g), and a prediction set (RMSEP = 0.11408 mg/g). For an acetone solution of 0.003 mg/g, the mean absolute percentage error (MAPE) was the lowest among the three quantitative models. For a concentration of 7.29 mg/g, the MAPE was 1.60%. This method achieved limits of quantification and detections of 0.003 mg/g and 1 μg/g, respectively. In general, these results suggested that ZnO NPs@Ag NWs as SERS substrates coupled with PLS simply and accurately quantified trace acetone concentrations in transformer oil.

Surface-enhanced Raman spectroscopy combined with stable isotope probing to assess the metabolic activity of Escherichia coli cells in chicken carcass wash water

Rapid evaluation of the metabolic activity of microorganisms is crucial in the assessment of the disinfection ability of various antimicrobial agents in the food industry. In this study, surface-enhanced Raman spectroscopy combined with isotope probing was employed for the analysis of the disinfection of single bacterial cells in the chicken carcass wash water. The Raman signals from single Escherichia coli O157:H7 cells were enhanced by in situ synthesis of silver nanoparticles. The ΔCD of the cells grown in presence of 0.5% hydrogen peroxide and 50 ppm chlorine was 5.86 ± 1.86% and 5.1 ± 2.3%, respectively, which showed significant reduction compared with cells grown in the absence of disinfecting agents (19.86 ± 2.51%) after 2 h of incubation. The study proved that the proposed method had the potential to assess the metabolic activity of microorganisms in other food products and optimize the disinfection process.

LSPR Tunable Ag@PDMS SERS Substrate for High Sensitivity and Uniformity Detection of Dye Molecules

At present, the use of efficient and cost-effective methods to construct plasmonic surface-enhanced Raman scattering (SERS) substrates of high sensitivity, uniformity and reproducibility is still crucial to satisfy the practical application of SERS technology. In this paper, a localized surface plasmonic resonance (LSPR) tunable flexible Ag@PDMS substrate was successfully constructed by the low-cost bio-template-stripping method and magnetron sputtering technology. The theory proves that the local electromagnetic field enhancement and "hot spot" distribution is adjustable by modifying the size of the optical cavity unit in the periodicity nanocavity array structure. Experimentally, using rhodamine 6G (R6G) as the target analyte, the SERS performance of optimal Ag@PDMS substrate (Ag film thickness for 315 nm) was researched in detail, which the minimum detection limit was 10^-11 M and the enhancement factor was calculated as 8.03 × 10⁸, indicating its high sensitivity. The relative standard deviation (RSD) was calculated as 10.38%, showing that the prepared substrate had excellent electromagnetic field enhancement uniformity. At last, the trace detection of Crystal violet (CV, LOD = 10^-9 M) and the simultaneous detection of three common dyes (R6G, CV and Methylene blue (MB) mixture) were also realized. This result suggests that the SERS substrate has a good application prospect in the quantitative and qualitative detection of dye molecules.

Rapid Immobilization of Silver Nanoparticles via Amino-quinone Coatings Enables Surface-Enhanced Raman Scattering Detection

Immobilization of metal nanoparticles (NPs) on flexible substrates for surface-enhanced Raman scattering (SERS) has received great attention. Anchoring NPs on substrates generally involves the process of surface modification, thanks to its simple, universal, and nondestructive features. 2-Hydroxy-1,4-naphthoquinone (HNQ), a plant-derived compound used to dye hairs and nails, may interact with polyamine or metal ions to form a surface coating. Here, we report the formation of amino-quinone coatings via the co-deposition of HNQ and polyethyleneimine, which provides a functionalized platform to rapidly immobilize Ag NPs on substrates such as a poly(dimethylsiloxane) (PDMS) film to fabricate Ag-PDMS substrates for SERS detection. The detection concentrations are down to 10^-8 M for rhodamine 6G. This work expands the system of surface co-deposition and further provides a facile route to prepare a highly efficient SERS substrate.

Optical sensing techniques for rapid detection of agrochemicals: Strategies, challenges, and perspectives

In recent years, the irrational use of agrochemicals has caused great harm to the environment and public health. Along with the rapid development of optical technology and nanotechnology, the research of optical sensing methods in agrochemical detection has been developed rapidly owing to its advantages of simplicity, fast response, and cost-effectiveness. In this review, the strategies of employing optical systems based on colorimetric sensor, fluorescence, chemiluminescence, terahertz spectroscopy, surface plasmon resonance, and surface-enhanced Raman spectroscopy for sensing agrochemicals were summarized. In addition, the challenges in the practical application of optical sensing technologies for agrochemical detection were discussed in-depth, and potential future trends and prospects of these techniques were addressed. A variety of nanomaterials have been developed for enhancing the sensitivity of optical sensing systems. The optical properties of nanomaterials are governed by their size, shape, and chemical structure. Although each optical sensing system holds its advantages, there are still many challenges that need to be overcome in practical applications. With the continuous developments in novel functional nanomaterials, sample preparation methods, and spectral processing algorithms, optical sensors are expected to have powerful potential for rapid testing of agrochemicals in the environment and foods.

Flexible surface-enhanced Raman scatting substrates: recent advances in their principles, design strategies, diversified material selections and applications

Surface-enhanced Raman scattering (SERS) is widely used as a powerful analytical technology in cutting-edge areas such as food safety, biology, chemistry, and medical diagnosis, providing ultra-fast, ultra-sensitive, nondestructive characterization and achieving ultra-high detection sensitivity even down to the single-molecule level. Development of Raman spectroscopy is strongly dependent on high-performance SERS substrates, which have long evolved from the early days of rough metal electrodes to periodic nanopatterned arrays building on solid supporting substrates. For rigid SERS substrates, however, their applications are restricted by sophisticated pretreatments for detecting solid samples with non-planar surfaces. It is therefore essential to reassert the principles in constructing flexible SERS substrates. Herein, we comprehensively review the state-of-the-art in understanding, preparing and using flexible SERS. The basic mechanisms behind the flexible SERS are briefly outlined, typical design strategies are highlighted and diversified selection of materials in preparing flexible SERS substrates are reviewed. Then the recent achievements of various interdisciplinary applications based on flexible SERS substrates are summarized. Finally, the challenges and perspectives for future evolution of flexible SERS and their applications are demonstrated. We propose new research directions focused on stimulating the real potential of SERS as an advanced analytical technique for commercialization.