Search

Despite prohibition in many countries, malachite green (MG) and crystal violet (CV) are illegally used in aquaculture, endangering both human health and the environment. Therefore, it is crucial to develop a method to accurately detect MG and CV. Surface-enhanced Raman spectroscopy (SERS) technology based on noble metal materials has attracted considerable attention for detecting food contaminations. However, noble metal materials are of poor stability and have a very low affinity for organic molecules. Herein, in this study, covalent organic frameworks (COFs) modified with silver nanoparticles (Ag NPs) were used as SERS substrates for the adsorption and detection of fungicides. COFs prepared by the Schiff base reaction of 1,3,5-tris (4-aminophenyl) benzene (TAPB) and 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMTA) had a huge specific surface area and could provide sufficient adsorption sites and Ag NPs grown on the surface of COFs not only generated dense SERS "hot spots" but also improved their stability. The results showed that COF@Ag NPs exhibited a high enhancement factor (1.4 × 106), high reproducibility (RSD = 6.18%), and good stability within 50 days (RSD = 8.88%). Regression analyses in the ranges of 0.0001–10.0 mg/L and 0.0002–10.0 mg/L showed that the limits of detection (LOD) for the standard solutions of MG and CV were 3.8 × 10−5 mg/L and 1.8 × 10−5 mg/L, respectively. Furthermore, for MG and CV in fish samples, significant recoveries of 90.83–107.91% and 98.60–116.69% were achieved. Hence, it is hoped that this work could expand the application of COF materials for trace detection in SERS analyses. [ABSTRACT FROM AUTHOR]

In conclusion, this study has successfully developed a novel SERS substrate using Fe3O4@UiO-66(Zr)@Ag nanoparticles for the detection of OPs in food samples. In this work, a new SERS substrate, Fe3O4@UiO-66(Zr)@Ag nanoparticles (FUAs), was developed and applied for trace detection of organophosphorus pesticides (OPs) in food. Surface-enhanced Raman spectroscopy (SERS) has attracted much attention as a rapid, sensitive, and non-destructive method for trace analysis, especially in food and biological samples (Yun et al., 2012). [Extracted from the article]

Plasmonic Au–Ag core–shell nanorods (Au@Ag NRs) have drawn great attention and are widely used in surface-enhanced Raman scattering (SERS) due to their distinctive local surface plasmon resonance peculiarities. To optimize the thickness of the Ag shell, the electromagnetic field distribution of Au@Ag NRs was firstly simulated using the Radiofrequency module of COMSOL. Then, Au@Ag NRs with different shell thicknesses were prepared by coating different amounts of silver nitrate, and the Raman signal of the molecule of 4-mercaptobenzoic acid was measured to evaluate the SERS activity of the prepared Au@Ag NRs. The experimental results showed that the Au@Ag NRs with the shell thickness of 7.51 nm performed the best SERS effect. Finally, the optimized Au@Ag NRs were used to detect thiram solution and a low limit of detection of 0.003 mg/L was achieved, indicating that the optimized Au@Ag NRs might be a promising substrate for pesticide residues detection. [ABSTRACT FROM AUTHOR]

Malachite green (MG) abuse in aquaculture has caused food safety issues and surface‐enhanced Raman scattering (SERS) can be utilized to monitor MG residues in aquatic products. However, the sensitivity and accuracy of SERS detection are limited by food matrix interference. Therefore, in this study, SERS active MNP@Au@MIL‐100(Fe) substrates were developed by utilizing magnetic nanoparticle (MNP) as the core, which was evenly decorated with Au nanoparticles (AuNPs), and then coated with metal–organic frameworks (MOFs) shell of MIL‐100(Fe), which acted as a filter to only allow molecules with appropriate sizes to approach the inner AuNPs, thus avoiding food matrix interference and improving the identification ability to analytes. Experiments in detecting MG residues in prawns was realized with the limit of detection (LOD) of 1.32 × 10−10 M, showing great potential for its use as a reliable SERS substrate for monitoring food contaminants. [ABSTRACT FROM AUTHOR]

Frozen foods are among the most popular food products and the development of techniques for the rapid detection of their structures and quality is important for the frozen food industry. In the current review, the principles and applications of Raman spectroscopic techniques in detecting and evaluating the structure changes and quality of frozen foods are discussed and merits and drawbacks of each Raman type are presented. These techniques include dispersive, Fourier transform, spatially offset, micro Raman spectroscopies. Raman spectroscopy can assess the compositional, physicochemical, and sensory characteristics of the frozen foods without any pretreatment. It can also be applied to investigate the structural alterations of protein, lipid, water and other components. Further trends of developing the Raman spectroscopy in monitoring the frozen foods should focus on reducing overlapping signals, achieving real noninvasive detection, eliminating misclassification and quantification errors, establishing standardized Raman database, and controlling cost. [ABSTRACT FROM AUTHOR]

Modification of surface-enhanced Raman spectroscopy (SERS) substrates with thiol ligands is an emerging approach in enhancing the stability and sensitivity of metal substrates due to their good affinity with metals such as Au, Ag, and Cu. Thus, in the current study, 2-mercaptoethanol was used to modify the surface of silver-coated gold nanoparticles to develop a novel SERS substrate for the rapid assessment of fungicide residues in fruit samples. Results showed that the substrate could achieve the detection of ferbam and thiabendazole residues in apple puree with limits of detection of approximately 0.0042 and 0.0064 ppm, high coefficients of determination of 0.9946 and 0.9968, good recoveries ranging from 80 to 105 and 81 to 107% and relative standard deviations of 3.5–7.5 and 3.8–7.9 %, respectively. Therefore, the substrate developed could potentially be utilised to assess other toxic agrochemicals in future. [ABSTRACT FROM AUTHOR]

The frequent occurrence of food safety incidents has given rise to unprecedented concern about food contamination issues for both consumers and the industry. Various contaminations in food pose serious threats to food safety and human health. Many detection methods were studied to address the challenge. Recently, biosensors relying on deoxyribonucleic acid (DNA)-functionalized nanoparticles have been developed as an efficient and effective detection method. In the current review, the strategies for DNA assembly metal and metal oxide nanoparticles are elaborated, recent applications of the sensors based on DNA-functionalized nanoparticles in food contaminant detection are discussed. Pathogenic bacteria, heavy metal ions, mycotoxins, antibiotics, and pesticides are covered as food contaminants. Additionally, limitations and future trends of functionalized nanoparticles-based technology are also presented. The current review indicates that DNA-functionalized metal and metal oxide nanoparticles are a novel nanomaterial with unique biological and physical properties for developing electrochemical, fluorescent, colourimetric and surface-enhanced Raman spectroscopy (SERS) sensors, etc. Compared with conventional detection techniques, DNA-functionalized metal and metal oxide nanoparticles have considerable advantages with high accuracy, high specificity, micro-intelligence, and low cost. Nevertheless, the stability of these sensors and the limitations of real-time detection are still under discussion. Therefore, more tolerant, portable, and rapid DNA sensors should be developed to better the real-time monitoring of harmful contaminants. [ABSTRACT FROM AUTHOR]

Food safety is directly relevant to human health and has drawn the intense attention of the public. Surface-enhanced Raman scattering (SERS), as a rapid and facile technology, has been widely employed for food safety detection. SERS substrates, as an important part of this technology, greatly influence SERS performance. Currently, porous materials (PSM) nanohybridized with metal nanoparticles (MNPs) (PSM/MNPs) for serving SERS substrates have attracted great interest due to their excellent merits in the improvement of SERS sensitivity, specificity and stability, posing a great potential for rapid and in-situ detection for food contaminants in complex food matrixes. In this review, the types and synthesis methods of PSM available for the fabrication of SERS substrates, which include porous carbon (PC), porous silicon/silica (PS/PSiO 2), metal-organic frameworks (MOFs), high polymer, semiconductor, cellulose and other porous materials are introduced and their nanohybridization methods with MNPs are discussed. In addition, recent applications of PSM/MNPs for enhancing SERS detection in food safety areas such as pesticide and veterinary drug residues, illegal additives, foodborne bacteria, mycotoxin, spoilage markers and heavy metals are also presented, and future challenges and potential solutions are finally detailed in the current review. Compared to non-porous materials, porous materials with high porosity and large surface specific area prevent MNPs from aggregation and increase the adsorption of the target analyte, leading to the improvement in stability and sensitivity of SERS substrates. Moreover, adjustable pore sizes in these substrates enable the selective absorption of specific molecules, blocking interference of big molecules. On the other hand, multiple scattering from the porous structure enhances SERS intensity, leading to high sensitivity for analytes. Recent applications in detecting various food hazards show the promising prospect of PSM/MNPs for sustainable, environmentally friendly and large-scale detection for ensuring food safety. • Porous materials can be nanohybridized with metal nanoparticles as SERS substrates. • Different synthesis methods of various porous SERS substrates are summarized. • Porous SERS substrates will promote the detection of food contaminants. • Developing porous SERS substrates remains a challenge. [ABSTRACT FROM AUTHOR]

Fresh fruit are important for a healthy diet, however, their shelf-life can be shortened because of ethylene, a key phytohormone associated with the ripening process. Therefore, detecting ethylene concentration on trace level and regulating its activity by safe and effective approaches are of paramount importance in extending postharvest shelf-life and controlling maturity of fruit. In this review, ethylene detection technologies as well as ethylene regulating strategies are discussed, aiming to develop more innovative and effective approaches. Effects of ethylene on quality and shelf-life of fruit are presented. Ethylene detection and monitoring technologies available such as gas chromatography, electrochemical, optical, chemical methods, especially novel methods such as those based on colorimetric, luminescence, metal-organic frameworks, organic field effect transistors and surface enhanced Raman spectroscopy are described. In addition, shelf-life extending technologies for ethylene control, removal or inhibition such as suppressing ethylene synthesis, scavenging or oxidizing or adsorbing ethylene, and blocking ethylene receptor are summarized. Finally, future perspectives on developing strategies that can simultaneously satisfy the requirements of sensitivity, rapidness and on-line for wide utilization in ethylene monitoring of fresh products are also given. It is expected that miniature and sensitive ethylene detection techniques combined with feasible ethylene control methods should be an effective solution for fruit quality maintenance and shelf-life extension. However, each type of sensors and ethylene control strategies currently available has their own advantages and limitations. Therefore, attempts should be made to exploit more effective ethylene detection and controlling technologies. • Ethylene concentration affects postharvest shelf-life and maturity of fruit. • Detecting and regulating C 2 H 4 is important in fruit postharvest management. • Commercially available C 2 H 4 detection methods have specific application fields. • Nanotechnology should be employed to achieve in-situ and rapid C 2 H 4 detection. • Dynamic controlled atmospheres can be refined to avoid CO 2 and low O 2 injury. [ABSTRACT FROM AUTHOR]

In the current work, surface-enhanced Raman scattering (SERS) based on gold nanoparticles (AuNPs) and silver-coated gold nanoparticles (Au@AgNPs) with coffee ring effect was employed to simultaneously ascertain urea and ammonium sulfate (AmS) in milk. A small drop (2 µL) of milk with adulterants was dried on a gold-coated slide to examine concentrations ranging from 5, 10, 20, 40 and 80 mg/dL based on spectra ranging from 400 to 1500 cm.−1 A uniform distribution of analytes, with enhanced Raman signals was detected in a small region (maximum 1.9 mm) of coffee ring across the centre of coffee ring pattern. Nanoparticles with core (Au) diameter of 26 nm and shell thickness (Ag) of 6.5 nm were confirmed using transmission electron microscopy (TEM) images. A strong Raman peak at 980 cm−1 was assigned to AmS, while that at 1001 cm−1 was ascribed to urea. With AuNPs, coefficients of determination (R2) of 0.9873 and 0.9859 were achieved for urea and AmS, respectively, while for Au@AgNPs values of 0.9827 and 0.9855 were obtained for urea and AmS, respectively. This study revealed that SERS based on coffee ring effect has the potential to be further exploited for detecting other banned and hazardous adulterants in milk and milk products. [ABSTRACT FROM AUTHOR]

Abstract The residual of pesticides in fruit and vegetables is one of the major food safety concerns for consumers. There is a demand for easy and rapid analytical methods to sense pesticide residues in foods. In this study, a core-shell Au@Ag nanoparticles aggregates (Au@AgNAs) based surface-enhanced Raman scattering (SERS) method was developed to detect trace amount of difenoconazole. Results suggested that by targeting the characteristic peaks at 700 and 808 cm−1, the logarithmic SERS signal intensities and logarithmic difenoconazole concentrations in the range from 5 × 10−7 to 2.5 × 10−5 M showed linear relationship with the coefficient of determination (R 2 ) of 0.990 and 0.985, and limit of detection (LOD) values of 5.01 × 10−8 and 2.8 × 10−8 M, respectively. The Quick Easy Cheap Effective Rugged and Safe (QuEChERS) sample preparation method was used to extract difenoconazole in grapes for SERS measurements. The LOD of difenoconazole in grapes using this developed method was as low as 48 μg/kg, which was significantly lower than the maximum residue limit (MRL) values prescribed by European Union and China. This study demonstrated that the Au@AgNAs-based SERS method can be used as a simple, rapid and sensitive approach for sensing trace contaminants in food. Graphical abstract fx1 Highlights • SERS is an alternative method for rapidly detecting trace contaminants. • Au@Ag nanowire aggregates was used as SERS substrate for detecting pesticide. • The developed SERS method can detect as low as 48 μg/kg difenoconazole in grapes. • The entire analysis can be achieved within 25 min. [ABSTRACT FROM AUTHOR]

The ability to analyze food safety and quality in a quick, sensitive, and reliable manner is of high importance in food industry. Surface-enhanced Raman scattering (SERS), which is popular for its significant enhancement, excellent sensitivity, and the fingerprinting ability to identify special molecules, has shown vast potential for rapid detection of chemical constitutes, chemical contaminants, and pathogens in food sample. For SERS, the enhancement of Raman signals is related to not only the SERS-active substrates, but also the interactions between sample and substrates. In the current review, colloidal and solid surface-based substrates are briefly described, fabrication techniques for SERS substrates are presented, and applications of SERS for food matrixes, correlation between substrates and food samples are also introduced. Finally, some outlook on further developments is presented. The current review is therefore intended to provide a comprehensive overview on the nanofabrication of SERS substrates, and the potential of applying SERS as an important food analysis platform. [ABSTRACT FROM AUTHOR]

Background The irrational usage of chemical substances including pesticides and drugs in agricultural and food production is a significant food safety issue due to its residues. Therefore, the detection of harmful residues in foods is an indispensable step for guaranteeing the consumer's health. Conventional methods, such as HPLC, GC-MS and LC-MS are accurate enough, but they fail to meet the requirements of the modern industry for rapid and on-line detection. Novel reliable techniques should thus be developed as alternatives. Scope and approach In this review, fundamentals of surface-enhanced Raman spectroscopy (SERS) is introduced. Recent advances in its usage for detecting harmful chemical residues in agricultural products including pesticides, antibiotics and β 2 -adrenergic agonists are discussed by two typical ways of detection improvement, and the advantages of SERS are addressed. Finally, future trends to routine use of SERS applications in harmful residues are presented. Key findings and conclusions SERS is a promising detection technique for the detection of common harmful chemical residues with merits of simple sampling, rapid data collection and non-destructiveness. Despite rapid developments in the technology, there is much studies should be done before SERS could be used as a daily tool for the industry. [ABSTRACT FROM AUTHOR]

• A high-sensitivity, stable and uniform Au@Ag NRs-CMC SERS chip was fabricated. • CMC hydrogel was used for Au@Ag NRs stabilization, homodisperse and protection. • Negatively-charged CMC hydrogel and Au@Ag NRs repel each other to form NRs arrays. • Au@Ag NRs-CMC chip has high SERS activity, reproducibility and long-term stability. • Au@Ag NRs-CMC chip achieves sensitive detection of pesticide residue in fruits. Cellulose material holds considerable promise for effective surface-enhanced Raman scattering (SERS) substrate construction due to its extensive availability, chemically modifying capacity, ease of manufacture, high flexibility and low optical activity. A large-area, high-sensitivity, stable and uniform Au@Ag nanorods (NRs)-CMC substrate was successfully developed via electrostatic repulsion by using negatively-charged core–shell Au@Ag NRs as SERS active plasmonic nanomaterial, combined with negatively-charged carboxymethylcellulose (CMC) hydrogel for nanoparticles stabilization, homodisperse and protection. The obtained Au@Ag NRs-CMC substrate showed excellent sensitivity for the detection of thiram residues in fruits containing low and abundant pigment interferents, such as apples and blueberries, with detection limits of 58 and 78 ppb, respectively. Additionally, it retained more than 80% SERS performance after storage for 9 months under ambient conditions, demonstrating its great potential in facilitating the commercialization of cellulose-based SERS technology for cost-effective detection of food contaminants with advantages of facile preparation procedure, uniformity, reproducibility and long-term stability. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) imaging coupling with multivariate analysis in spectral region of 200 to 1800 cm −1 was developed to quantify and visualize thiophanate-methyl (TM) and its metabolite carbendazim residues in red bell pepper ( Capsicum annuum L.). Least squares support vector machines (LS-SVM) and support vector machines (SVM) models based on seven optimized characteristic peaks that showed SERS effects of TM and its metabolite carbendazim residues were employed to establish prediction models. SERS spectra with first derivative (1st) and second derivative (2nd) method were subsequently compared and the optimized model of 1st-LS-SVM acquired showed the best performance (RPD = 6.08, R 2 P = 0.986 and RMSEP = 0.473). The results demonstrated that SERS imaging with multivariate analysis had the potential for rapid determination and visualization of the trace TM and its metabolite carbendazim residues in complex food matrices. [ABSTRACT FROM AUTHOR]

Aflatoxin B1 (AFB1) is a highly toxic mycotoxin that can contaminate foods. Hence, a surface-enhanced Raman scattering (SERS) and fluorescence dual signal-on biosensor was developed for AFB1 detection. Specifically, aminated mesoporous silica nanoparticles (MSNs) were used as nanocontainers to load the Rhodamine 6G (R6G) with fluorescence and Raman effects, aptamers and polydopamine (PDA) were sequentially assembled on the surface of the MSNs as dual-gated molecules, and MXenes and Au nanorods were used as SERS substrates. After adding AFB1 under acidic conditions, the degradation of PDA and specific bringing of the aptamer with AFB1 resulted in the release of R6G. Results showed that AFB1 could be quantified by Raman and fluorescence spectroscopic with detection limits of 0.133 pg mL−1 and 0.214 pg mL−1, respectively. Moreover, the biosensor could be applied to the detection of AFB1 in real peanut, maize and badam samples, providing a possible alternative solution for the detection of other analytes. [Display omitted] • Mesoporous silica biosensors with dual-gating molecules were constructed. • MXenes and Au nanorods substrates for SERS signal amplification were synthesized. • AFB1 could be quantified by integrating Raman and fluorescence techniques. • The results of the ELISA method verified the accuracy of the sensing platform. • A highly sensitive, label-free, and low-cost detection strategy is achieved. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • MNP@Ag-PEI microspheres were developed as SERS substrates for AFB1 detection. • Fluorescent dye cy5 was used as Raman and fluorophore (FL) reporters. • The preferential apt-cy5 and AFB1 binding caused changes in SERS and FL signals. • The dual-signal aptasensor possessed unique detection sensitivity and flexibility. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mesoporous silica coating was achieved on Au@Ag core–shell nanoparticles. • Au@Ag@mSiO 2 NP showed high enhancement ability for SERS detection. • Mesoporous silica coating provides selective screening based on molecular size. • Chloramphenicol was detected with a limit of detection of 6.68 × 10−8 M. • Au@Ag@mSiO 2 NP showed stability over long period of storage. 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@mSiO 2 NP) 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@mSiO 2 NP substrate for effective SERS detection of analytes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Recyclable SERS substrate of Fe 3 O 4 @MIL-100(Fe)@Ag was successfully synthesized. • This substrate can selectively detect and eliminate cationic dyes. • The detection limit of crystal violet was estimated to be as low as 14 ng/L. • This substrate can be reused at least 5 times. • This substrate exhibits excellent SERS activity, sensitivity, uniformity and stability. Recyclable surface-enhanced Raman scattering (SERS) substrates are beneficial to cost reduction and environmental protection and have always been a research topic with great interest. Herein, a core–shell-satellite structured SERS substrate Fe 3 O 4 @MIL-100(Fe)@Ag nanoparticles (FMAs) was developed, possessing versatile functionalities of adsorption, detection, degradation and recovery. Results showed that the MIL-100(Fe) with peroxidase-like activity as shell catalyzed H 2 O 2 to generate ·OH degraded pollutants within 5 min to achieve substrate cleaning, making FMAs recyclable for at least 5 times to sequentially detect different cationic dyes with high sensitivity, having low detection limits as low as 15.24 ng/L, 387.87 ng/L and 0.71 ng/g for crystal violet in deionized water, aquaculture water and tilapia, respectively. FMAs also showed good uniformity, reproducibility and stability, with a relative standard deviation value of 5.58 % between substrates and about 78.60 % SERS activity remained after 20 d storage at 4 °C. This FMAs substrate thus has great potential for selective detection of trace cationic dyes in food or other fields. [ABSTRACT FROM AUTHOR]

[Display omitted] • SERS-SIP was employed to analyze the metabolic activity of single E. coli cells. • In situ synthesis of silver nanoparticles were used for Raman signal enhancement. • Metabolically active cells could be distinguished as early as 2 h of incubation. • The metabolic activity of E. coli in chicken carcass wash water was tested. • Raman mapping of single E. coli cell was achieved. 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. [ABSTRACT FROM AUTHOR]

• AuNP dimers and MXenes exhibited good SERS enhancement and reproducibility. • The established SERS aptasensor allowed AFB1 detection over a wide linear range. • The novel AuNP dimers/MXenes assemblies constituted an efficient SERS platform. • This method has great potential for AFB1 detection in peanuts samples. Mycotoxin B1 (AFB1) contamination in agricultural products pose a deadly danger to animal and human health and its rapid and reliable detection is thus very important. Herein, a ratiometric surface-enhanced Raman scattering (SERS) aptasensor for AFB1 detection was developed, in which 1,2-bis(4-pyridyl) ethylene (BPE) was used to trigger the assembly of Au nanoparticle dimers (AuNP dimers) and form intensive SERS "hot spots", and MXenes nanosheets could load aptamer-modified AuNP dimers due to the hydrogen bonding and the chelation between the phosphate groups of aptamers and the Ti ion of MXenes. With the presence of AFB1 preferentially binding to AFB1 aptamer, AuNP dimers were separated from MXenes nanosheets, leading to a decrease in SERS intensity. Regression analysis in the range from 0.001 to 100 ng·mL−1 showed the limit of detection (LOD) being 0.6 pg·mL−1 in standard solution, indicating that the great prospects of the AuNP dimers/MXenes SERS substrate for detecting AFB1. [ABSTRACT FROM AUTHOR]

Efficient identification of pathogenic bacteria is greatly concerned with microbial food safety and foodborne diseases diagnosis. Surface-enhanced Raman scattering (SERS) tags are among the cutting-edge tools for bioanalysis, but facing troubles in either SERS sensitivity, durability, interfering signals, or universal recognition agents for target bacteria. This work proposed a multivariate scheme enabled by polyphenolic chemistry for the green synthesis, facile stabilization (functionalization), protective encapsulation, and bio-affinitive design of metal-phenolic networks (MPNs)-encapsulated silver SERS nanotags (AgNPs@4-mercaptobenzonitrile@MPNs). With remarkable SERS properties, shelf stability, and bacterial affinity, AgNPs@4-mercaptobenzonitrile@MPNs tags enabled rapid, reproducible, and interference-free SERS detection of two representative foodborne pathogens (i.e., E. coli O157: H7 and S. aureus) in the assistance of an aptamer-labelled magnetic probe, reaching good sensitivity and selectivity. Moreover, this SERS biosensor worked well in real food samples, manifesting the potential of polyphenolic chemistry in the customization of bio-affinitive SERS nanotags for food safety detection. [Display omitted] • Polyphenolic chemistry enabled from-synthesis-to-bioaffinity scheme of SERS tags. • Metal-phenolic networks acted as bioaffinity elements for bacterial recognition. • Polyphenolic SERS tags could be reliable detection probe for bacteria quantitation. • Polyphenolic SERS biosensor could detect foodborne bacteria down to 102 CFU/mL. • The SERS biosensor could work in milk and beef samples. [ABSTRACT FROM AUTHOR]

The development of flexible and robust plasmonic substrates has become a hot research topic in simplifying and extending the application of surface-enhanced Raman scattering (SERS) technique for real-world analysis. In this work, a facile method to fabricate an Au@Ag nanoparticle array sandwiched between the adhesive acrylic polymer tape and polyethene terephthalate (PET) film (T/Au@Ag/PET) as a high-performance SERS chip was reported for nondestructive detection of thiram on fruit peels. For this SERS chip, the ordered Au@Ag nanoparticle array formed by the self-assembly method was closely-packed, which generated high‐density sub‐3‐nm gaps and could produce high reproducible and sensitive SERS enhancement effects. The measurement of crystal violet with the limit of detection of 7.24 × 10−10 M was realized by targeting Raman shift at 1177 cm−1. Moreover, the excellent flexible feature of acrylic polymer tape enabled the substrate to withstand a tensile strain value of 20% for three cycles without significantly losing its SERS activity. By covering with a PET film, the SERS chip could maintain 87% SERS activity after storage for 60 days in the air environment, and could well withstand the influence of harsh conditions such as high temperature and ultrasound treatments. As a proof of the concept, the SERS tape was directly used to detect thiram on apple, tomato, and cucumber peels via a simple sampling-and-detection procedure, and the detection limit of 5 ng/cm2 was achieved. The T/Au@Ag/PET SERS chip should hold a promising candidate for food safety analysis in the future. Image 1 • The Au@Ag nanoparticle array was sandwiched between acrylic polymer tape and PET film. • Highly dense hotspots of the array ensured good performance for SERS detection. • The SERS chip showed excellent flexibility and storage stability. • The SERS chip was used for nondestructive detection of thiram in fruit peels. [ABSTRACT FROM AUTHOR]

Detection of bioactive metabolites produced by bacteria is important for identifying biomarkers for infectious diseases. In this study, a surface-enhanced Raman spectroscopy (SERS)-based technique was developed for the detection of bioactive metabolite indole produced by Escherichia coli (E. coli) in biological media. The use of highly sensitive Au@Ag core-shell nanoparticles resulted in the detection of indole concentration as low as 0.0886 mM in standard solution. The supplementation of growth media with 5 mM of exogenous tryptophan resulted in the production of a maximum yield of indole of 3.139 mM by E. coli O157:H7 at 37 °C. The growth of bacterial cells was reduced from 47.73 × 108 to 1.033 × 106 CFU/mL when the cells were grown in 0 and 10 mM exogenous tryptophan, respectively. The amount of indole in the Luria–Bertani (LB) media had an inverse correlation with the growth of cells, which resulted in a three-log reduction in the colony-forming unit when the indole concentration in the media was 20 times higher than normal. This work demonstrates that SERS is an effective and highly sensitive method for rapid detection of bioactive metabolites in biological matrix. Graphical Abstract [ABSTRACT FROM AUTHOR]

• A novel Fe 3 O 4 @NH 2 -MIL-101(Fe)@Ag SERS nanosensor was synthesized. • Aminated-MOF grew more Ag nanoparticles with stronger affinity for analyte. • The nanosensor exhibited good SERS sensitivity, reproducibility and stability. • The substrate was effective for trace detection of organophosphorus pesticides. 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 Fe 3 O 4 @NH 2 -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. [ABSTRACT FROM AUTHOR]

As a fingerprint-type recognition technique, surface-enhanced Raman spectroscopy (SERS) possessing the superior properties of rapid, ultrasensitive, multiplexed, non-destructive and portable natures is a more optimal spectroscopy candidate for quick food safety analysis. However, the majority of target contaminants in foods are Raman inactive with small Raman scattering cross-section or slow affinity towards the localized surface plasmon resonance (LSPR) areas. Various reactions are therefore studied to achieve the sensitive and selective SERS detection of trace and Raman inactive molecules. This review presents the concepts of various special chemical reactions involving changes in molecular structure or the breaking or formation of chemical bonds such as derivatization reactions, coordination reactions, association reactions and catalytic reactions for enhancing SERS detection. In particular, recent applications of these special chemical reactions combined with SERS techniques in food safety monitoring are discussed. In addition, challenges and future work of chemical reactions combined with SERS techniques in detection are also addressed. Various reactions have been proven to enhance SERS detection effectively through changing molecular vibrational mode, SERS substrate performance and the distance from signal molecules to substrates. Thus, various special chemical reactions can significantly widen the ranges of analytes to be detected by SERS, leading to possibly more widespread SERS applications in the food industry. In addition, operation simplicity and analysis speed of SERS detection are also improved with the assistance of various reactions, contributing to the development of portable SERS detection systems. • The concepts duand enhancement principles of reaction-enhanced SERS are discussed. • Recent applications of reaction-enhanced SERS in food safety monitoring are enumerated. • Challenges and future work of reaction-enhanced SERS method are suggested to shed new lights on development. [ABSTRACT FROM AUTHOR]

• A durian-shaped core-shell SERS substrate of Fe 3 O 4 @Au@Ag@Au was synthesized. • The SERS substrate had high SERS performance and good magnetic. • A "flow magnetic detection method" was proposed for non-destructive detection. • The DFAAA could be completely collected from the food surface with the new method. • The substrate could quantitatively detect the pesticide residues on food surface. A new type of durian-shaped Fe 3 O 4 @Au@Ag@Au (DFAAA) multilayer core-shell composite was prepared as an efficient surface-enhanced Raman scattering (SERS) substrate. The optimization process and SERS enhancement mechanism of the substrate were further explained with finite-difference time-domain simulation. The dense and uniform spiny array on the DFAAA surface had abundant "hot spots", greatly improving sensitivity, uniformity and reproducibility, with a Raman enhancement factor of 3.01 × 107 and storage-life of 30 d. A "flow magnetic detection method" was proposed to realize rapid and flexible detection of pesticide residues on the surface of different foods including fish and apple. The limit of detection of malachite green and thiram on the fish and apple surfaces were 0.13 and 0.18 ng/cm2, respectively. With its high SERS performance and good magnetic, the DFAAA possessed great application prospects as a facile SERS substrate for rapid and non-destructive detection of trace pesticide residues on foods. [ABSTRACT FROM AUTHOR]

Mycotoxin contamination in agri-food products compromises human and animal health throughout the supply chains, thus the establishment of rapid and accurate methods for the detection of mycotoxins is essential for food safety assurance. Among the preferred spectral methods, surface-enhanced Raman scattering (SERS) has emerged as an attractive solution for detecting trace mycotoxins in complex food matrices due to its advantages of high sensitivity, rapidness and non-destructiveness. However, relevant developments in research in this field are scarcely reviewed. In the current review, the fundamentals of SERS and substrates for detecting mycotoxin in agri-foods are introduced, technical developments in the detection procedure including combined techniques, fingerprinting and SERS tagging and spectral optimizations such as using chemometrics are elaborated. Recent applications of SERS methods for trace level detection of mycotoxins in agri-food samples including cereal grains, fruits, dairy products, and wine are also highlighted, and limitations and future prospects for developing the SERS technology for detecting mycotoxin contamination are finally presented. SERS is a rapid and sensitive technique for detecting trace mycotoxins. However, the preparation of high-performance SERS substrates for on-site quantitative analysis of real food samples is still a challenging scientific problem. Future research should focus on designing reliable SERS substrates, establishing SERS fingerprint libraries of mycotoxins, and developing accurate chemometric methods, and choosing suitable combined techniques in order to achieve an early adoption of the SERS method as a practical tool for detecting mycotoxin contamination in the agri-food industry. • Mycotoxin contamination in foods is a considerable challenge. • SERS technique can detect AFs, OTs, ZEN, DON, FB and other mycotoxins in foods. • SERS detection of mycotoxins includes fingerprinting and SERS tagging methods. • The speed and sensitivity of the SERS technique will facilitate mycotoxin inspection. [ABSTRACT FROM AUTHOR]

Food safety issues leading to severe healthy, economic and even social problems and detection of food contaminants has been attracting remarkable attention in recent decades. Surface-enhanced Raman scattering (SERS) is one of the most promising techniques to enable detecting contaminants at trace levels. Besides, with the emergence of global resource shortages and environmental problems, there is a growing demand for environmentally friendly and renewable resources. As a sustainable and biodegradable raw material, cellulose has aroused great interest and stimulated researchers to develop cellulose-based SERS substrates with novel functions. The review focuses on the utilizing of cellulosic materials for the design and preparation of various SERS substrates, including cellulose-papers, cellulose fabrics (CFs) and membranes, cellulose nanofibrils (CNFs), bacterial cellulose (BC), nanocrystalline cellulose (NCC), and surface-modified cellulose. The applications, challenges and potential solutions of these cellulose-based substrates in food safety detection are also presented, proposed and evaluated. For the complexity and diversity of multitudinous food systems, multiple approaches have been successfully employed to manufacture cellulose-based SERS substrates. Various types of cellulose with diverse morphology and mechanical properties make them customizable and integratable with multiple technologies in certain realistic applications. The explorations of SERS detections displaying excellent performances especially for the complex system/surface analysis with the capability of extraction, swabbing, transferring and concentrating target molecules from complexing food systems. The widespread application and prominent performance demonstrating the huge potential for cellulose-based materials to realize commercially viable, sustainable, flexible and green substrates in the near future. • Cellulose material is an excellent choice for SERS substrate design and fabrication. • Cellulose-based substrate is customizable in certain food safety inspection. • Cellulose can extract, swab, transfer and concentrate analytes from complex media. • Cellulose-SERS tests display good performances in complex food systems and surface. • Cellulose-SERS can realize commercial viable, in-situ, flexible and green detection. [ABSTRACT FROM AUTHOR]

Abstract Fast sampling and multicomponent detections are important in the analysis of pesticide residues detection. In this work, surface-enhanced Raman scattering (SERS) method based on silver-coated gold nanoparticles (Au@Ag NPs) was used to simultaneously detect multi-class pesticide residues such as thiacloprid (carbamate), profenofos (organophosphate) and oxamyl (neonicotinoid) in standard solution and peach fruit. The Au@Ag NPs with 26 nm Au core size and 6 nm Ag shell thickness exhibited significant Raman enhancement, especially by the creation of hot spots through NPs aggregation induced by the connection between Au@Ag NPs and target molecules. The findings demonstrated that the characteristic wavenumber of the pesticides (thiacloprid, profenofos, and oxamyl) could be precisely identified using the SERS method. Compared with earlier studies, the current approach was rapid, inexpensive and without lengthy sample pretreatment. Moreover, the results revealed that the limit of detection (LOD) was 0.1 mg/kg for thiacloprid obtained in the peach extract with determination coefficient (R2) of 0.986. Additionally, LOD for both profenofos and oxamyl was 0.01 mg/kg with a determination coefficient (R2) of 0.985 and 0.988, respectively. Good recovery percentage (78.6–162.0%) showed the high SERS activity with better accuracy for the detection of the thiacloprid, profenofos, and oxamyl in peach. The results of this study could offer a promising SERS platform for simultaneous detection of other contaminants such as thiacloprid, profenofos and oxamyl in multifaceted food matrices. Graphical abstract fx1 Highlights • Simultaneous detection of multi-class insecticide residues in peach was presented. • Multi-class detection of thiacloprid, profenfos and oxamyl is first time reported. • Au@Ag NPs was used as SERS substrate for detecting insecticides. • Proposed method can be used to simultaneously detect multiple insecticide in fruit. [ABSTRACT FROM AUTHOR]

Abstract A detection method for 17β-estradiol (E2) using surface-enhanced Raman scattering (SERS)-based aptamer sensor was presented. Raman reporter molecule Cy3 labeled E2-aptamer and DNA functionalized gold-silver core-shell nanoparticles (Au@Ag CS NPs) offered SERS with high sensitivity and selectivity. Based on the fabricated double strand DNA-immobilized gold-silver core-shell nanoparticles (Au@Ag NPs), SERS signal intensity of Raman reporter changed with the number of Cy3-labeled aptamer attached to the core-shell nanoparticles due to the strong binding affinity between the aptamers and E2 with different concentrations. A wide linear range from 1.0 × 10–13 to 1.0 × 10−9 was obtained for the detection of E2, with a low detection limit of 2.75 fM. This proposed method showed highly sensitive and selective for detecting E2, and could be used to determine E2 in actual samples. Graphical abstract fx1 Highlights • Double strand DNA functionalized core-shell nanoparticles were synthesized. • SERS-based aptamer sensor was proposed for detection of E2. • SERS intensity related to coordination reaction was characterized. • The proposed method exhibited good recovery, precision and accuracy. [ABSTRACT FROM AUTHOR]

• A high-sensitivity Au@AgNRs/CMC/qPCR flexible film SERS substrate was fabricated. • Au@AgNRs was synergistically stabilized and protected by CMC and qPCR bilayer film. • CMC stabilized Au@AgNRs through coordination of –COO– groups with surface Ag atoms. • qPCR film act as carrier and barrier to prevent Au@AgNRs from oxidation and damage. • The substrate was used for in-situ sampling and detection of thiabendazole on fruits. In this study, a high-performance, stable and homogeneous Au@AgNRs/CMC/qPCR flexible film surface-enhanced Raman scattering (SERS) substrate was constructed by synergistically stabilizing and protecting bimetallic core–shell Au@Ag nanorods (Au@AgNRs) with carboxymethylcellulose (CMC) and fluorescent-quantitative-polymerase-chain-reaction (qPCR) film. The network structure of CMC immobilized and aligned Au@AgNRs through coordination of carboxyl groups with surface Ag atoms to provide intensive and stable 'hot spots', and the qPCR bilayer film performed as carrier and barrier to protect Au@AgNRs from oxidation, humidity and optical damage and improved the robustness and stability. The Au@AgNRs/CMC/qPCR film was used for in-situ extraction and SERS detection of thiabendazole on nectarine (0.24 ppm) and lemon (0.27 ppm) with low detection of limits. Furthermore, it retained 98.6% SERS performance after storage for 90 days under ambient conditions, revealing the great potential in promoting the commercialization of the SERS technique for sensitive contaminants sensing with simple fabrication procedures, homogeneity, reproducibility and long-term stability. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) technique is widely used in the field of food detection due to its rapidity, non-destructiveness and high sensitivity. However, non-recyclable substrates are limited in their practical detection application owing to high-cost and environmental pollution. Therefore, it is crucial to design SERS substrates that are recyclable and highly sensitive. Semiconductors with photocatalytic degradation capabilities have become attractive materials for the detection of contaminated residues in complex food matrices due to their high photocatalytic efficiency and environmental friendliness. Nevertheless, relevant research advances in this field have not been reviewed. In this review, the basic principles of SERS and semiconductor photocatalysis are introduced. The various constituent structures of semiconductors used for SERS substracts are described, including pure semiconductors, semiconductor-Ag/Au hybrid structures, and semiconductor-transition metal/semiconductor heterostructures. Then, the application of recyclable substrates for SERS detection of pesticides, dyes, antibiotics, heavy metals and other contaminants in agri-food products is then elaborated. Finally, the limitations and prospects of recyclable SERS substrates are presented. Photocatalytic semiconductors are potential candidates for the preparation of highly sensitive and recoverable SERS substrates. However, the development of recyclable SERS substrates for real sample detection remains a challenging scientific problem. Future research should focus on preparing novel photocatalytic semiconductor heterojunctions, investigating substrate interface catalytic processes and exploring the effects of complex food substrates on substrate recycling performance to improve the versatility of substrates and make them practical tools for the detection of food contaminants in the agri-food industry. • Photocatalytic semiconductors can be used to prepare recyclable SERS substrates. • Different structures of semiconductor recyclable SERS substrates are summarised. • Semiconductor SERS substrates will facilitate the detection of food contaminants. • Developing recyclable SERS substrates remains a challenge. [ABSTRACT FROM AUTHOR]

Background Surface-enhanced Raman spectroscopy (SERS) techniques are becoming increasingly widespread and accessible for accurate and specific identification of chemical or microbiological contaminants in foodstuffs. However, the consistency and repeatability of SERS-based techniques is a challenge due to complicated detection environments. This drawback can be overcome by integrating the SERS detection into a microfluidic platform, which can provide a continuous flow condition for highly reproducible SERS measurements. Furthermore, the SERS-microfluidic platform can perform elaborating sample pre-treatments, showing great potentials for on-situ analysis of food contaminants. Scope and approach This review mainly summarizes the principles and methods of SERS-microfluidic systems, as well as their applications in rapid analysis of food contaminants. Three ways of integrating SERS substrate into microfluidic channels are highlighted. Finally, the main challenges and future efforts in developing SERS-microfluidic systems for on-situ food contaminants detection are discussed. Key findings and conclusions SERS-microfluidic platform conforms to the development tendency of modern analytical technology, and has great potentials for rapid analysis of food contaminants. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new MOF-based SERS substrate of Fe 3 O 4 @UiO-66(Zr)@Ag NPs was synthesized. • Component advantages in the substrate were brought into play synergistically. • The substrate had excellent SERS detection sensitivity, uniformity and stability. • The substrate realized organophosphorus trace detection in water and apple juice. Surface-enhanced Raman spectroscopy (SERS) technology has been revived and developed with the introduction of metal–organic frameworks (MOFs), while more valuable properties of MOFs for SERS substrates remain largely unexplored. This work constructed a new SERS substrate Fe 3 O 4 @UiO-66(Zr)@Ag nanoparticles (FUAs) with excellent SERS detection sensitivity, uniformity, reproducibility and stability, exhibiting a high Raman enhancement factor (5.62 × 106), low limit of detection (LOD, 2.11 × 10-11 M) and RSD (12.41 %) for 4-NBT, and maintaining 81 % SERS activity within 60 days. The FUAs took full advantage of the strong affinity of UiO-66(Zr) for organophosphorus pesticides (OPs) to realize trace OPs detection. The LODs of phoxim, triazophos and methyl parathion in apple juice were 0.041, 0.021 and 0.0031 mg/L, respectively, with good linearities ranging from 0.02 or 0.1–50 mg/L, meeting the requirements of the food control standards, indicating that the potentials and prospects of the FUAs SERS substrate for trace detecting OPs in foods. [ABSTRACT FROM AUTHOR]

[Display omitted] • MoS 2 @TiO 2 @Au heterojunction-based recyclable SERS platform was synthesized. • MoS 2 @TiO 2 @Au exhibited high photocatalytic activity for fungicides degradation. • The in-situ monitoring photodegradation of fungicides were realized. • MoS 2 @TiO 2 @Au could serve as photocatalytic recyclable SERS substrate. 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 (MoS 2 @TiO 2 @Au) as a heterojunction-based recyclable SERS platform was fabricated for the efficient determination of fungicides. Results showed that the MoS 2 @TiO 2 @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 MoS 2 @TiO 2 @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. [ABSTRACT FROM AUTHOR]

Microbiological safety of food is closely related to the activities of foodborne microorganisms, which is among the critical issues in the food industry that require careful screening. A series of analytical techniques have been employed for microbiological food safety detection but renders either analytical defects or practical limitations. With the sensitive and fingerprint sensing ability of surface-enhanced Raman scattering (SERS) technique and the easy operations of magnetic entities (MEs), SERS-based magnetic platforms (MagSERS) emerge as a potent candidate for the analysis of microbiological foodborne hazards. The current review focuses on the fundamentals and recent applications of MagSERS in microbiological safety of food. In this review, the design and fabrication of MagSERS are introduced, which comprises the functionalized MEs plus noble-metal SERS substrates, magnetic nanocomposites plus noble-metal SERS substrates, and magnetic SERS substrates, and the detection principles of MagSERS are illustrated in detail, including the combination of magnetic capture, separation, and enrichment of targets (via recognition elements functionalized MEs) with SERS substrates, as well as the magnetism-mediated hotspot engineering of SERS substrates. In addition, the current advances in MagSERS methods for detecting foodborne bacteria, biological toxins, and viruses are summarized and future perspectives for the food industry are also given. Key findings and conclusions : As demonstrated by the publications in the field, MagSERS that merges magnetic properties and SERS spectra can facilitate the detection of foodborne biohazards for their excellent target separation and enrichment (sampling), simplified assay procedures (assaying), optimized SERS effect and signal or signalling. As such, MagSERS platforms show a promising prospect in the construction of more simple, rapid, and sensitive biosensors for food safety. • Design, fabrication, and principles of diverse types of MagSERS are presented. • Current advances and future trends of MagSERS for food bioanalysis are proposed. • MagSERS is featured with simple sampling, rapid assaying, and sensitive signalling. • MagSERS can be used for assaying foodborne bacteria, biotoxins, and viruses. [ABSTRACT FROM AUTHOR]

Food safety has attracted considerable attention in recent years. As a rapid, fingerprint-type recognition and nondestructive detection technique, surface-enhanced Raman scattering (SERS) has been among the promising techniques to meet the increasing needs for food safety analysis. Currently, emerging flexible SERS substrates as an alternative for colloidal and rigid SERS substrates have received great interest. Flexible SERS substrates possess the advantages of easy sampling by wrapping or swabbing on nonplanar surfaces, which facilitate the detection of contaminants from food surfaces and shed new lights on the nondestructive and sensitive detection of food analytes. In this review, the characteristics of different flexible materials such as cellulose, polymer film, cotton fabric, adhesive tape and bio-materials for constructing flexible SERS substrates are introduced, detection strategies including infiltration scheme, swab-sampling and in-situ detection are discussed, and recent applications of flexible SERS substrates in detecting trace pesticides in fruits and vegetables, chemical residues in animal farming including fungicides and antibiotics, illegal food additives and food-borne pathogens are highlighted. Flexible SERS substrates have been increasingly studied for detecting food contaminants. In preparing SERS substrates, different properties of the materials should be considered. For the detection strategies, compared with conventional infiltration scheme, swab-sampling is unique for flexible substrates and can collect target molecules directly from the surface, while in-situ detection is the most convenient, facile and nondestructive. Encouraging application results available show that flexible SERS substrates possess enormous potentials for food safety analysis and surveillance. • Flexible SERS substrates can provide rapid and nondestructive detection for foods. • Materials for constructing flexible SERS substrates are highlighted. • Different detection strategies using flexible SERS substrates are compared. • Recent applications of flexible SERS substrates in food safety are summarized. • Challenges and development of flexible SERS substrates are discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • A 3D gold nanoparticles spherical liquid array was constructed for SERS analysis. • Chloroform produced an inherent characteristic peak to correct signal fluctuation. • The prepared SERS substrate is capable of measuring diverse polarities. • This assay provides a rapid and sensitive way of detecting triazophos in apples. High-performance plasmonic substrates have recently attracted much research attention. Herein, a three-dimensional gold nanoparticles (AuNPs) spherical liquid array (SLA) with high "hot spots" and tunable nanometer gap by optimizing the proportion of AuNPs colloids over chloroform was synthesized based on a water–oil interfacial self-assembly strategy. The substrate demonstrated excellent surface-enhanced Raman scattering (SERS) performance using tetrathiafulvalene and rhodamine 6G (R6G) as probe molecules. With a simple extraction and soaking pretreatment process, the SLA exhibited high sensitivity for analysing triazophos on apple peels, with a limit of detection (LOD) of 0.005 µg/mL and recovery ranging from 96 to 110 %. Particularly, the chloroform produced an inherent characteristic peak at 665 cm−1, which was used as the internal standard to correct SERS signal fluctuation, leading to an improvement of the corresponding coefficient R2 from 0.97 to 0.99, thus improving the reproducibility. Therefore the SLA substrate possesses the potential for quantitative analysis of food contaminants. [ABSTRACT FROM AUTHOR]