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[Display omitted] • A highly sensitive, specific, and low-cost detection strategy was developed. • G4-DNAzyme added Cas12a system achieved a simultaneous output of three signals. • G4-DNAzyme-based sensor realized smartphone-assisted portable detection of AFB1. • The sensor correctly identified negatives and positives from peanut samples. Aflatoxin B1 (AFB1) contamination severely threatens human and animal health, it is thus critical to construct a strategy for its rapid, accurate, and visual detection. Herein, a multimodal biosensor was proposed based on CRISPR/Cas12a cleaved G-quadruplex (G4) for AFB1 detection. Briefly, specific binding of AFB1 to the aptamer occupied the binding site of the complementary DNA (cDNA), and cDNA then activated Cas12a to cleave G4 into fragments. Meanwhile, the intact G4-DNAzyme could catalyze 3, 3′, 5, 5′-tetramethylbenzidine (TMB) to form colourimetric/SERS/fluorescent signal-enhanced TMBox, and the yellow solution produced by TMBox under acidic conditions could be integrated with a smartphone application for visual detection. The colourimetric/SERS/fluorescent biosensor yielded detection limits of 0.85, 0.79, and 1.65 pg·mL−1, respectively, and was applied for detecting AFB1 in peanut, maize, and badam samples. The method is suitable for visual detection in naturally contaminated peanut samples and has prospective applications in the food industry. [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]

[Display omitted] • 2D-image data were obtained from 1D-spectra data using GASF, GADF, MTF and RP. • 1D-CNN and 2D-CNN models were developed to distinguish PCRs of different origins. • Con-CNN and Add-CNN models were built to fuse 1D-spectra data and 2D-image data. The geographical indication of pericarpium citri reticulatae (PCR) is very important in grading the quality and price of PCRs. Therefore, terahertz time-domain spectroscopy (THz-TDS) technology combined with convolutional neural networks (CNN) was proposed to distinguish PCRs of different origins without damage in this study. The one-dimensional CNN (1D-CNN) model with an accuracy of 82.99% based on spectral data processed with SNV was established. The two-dimensional image features were transformed from unprocessed spectral data using the gramian angular field (GAF), the Markov transition field (MTF) and the recurrence plot (RP), which were used to build a two-dimensional CNN (2D-CNN) model with an accuracy of 78.33%. Further, the CNN models with different fusion methods were developed for fusing spectra data and image data. In addition, the adding spectra and images based on the CNN (Add-CNN) model with an accuracy of 86.17% performed better. Eventually, the Add-CNN model based on ten frequencies extracted using permutation importance (PI) achieved the identification of PCRs from different origins. Overall, the current study would provide a new method for identifying PCRs of different origins, which was expected to be used for the traceability of PCRs products. [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]

[Display omitted] • Raman-SIP was used to analyze the metabolic activity of a single E. coli cell. • Second derivative spectra resulted in deconvolution of broad Raman peaks. • Total cell metabolic activity varied according to the carbon source available. • The substrate-dependent change in macromolecule composition of cells was analyzed. Metabolic dynamics of bacterial cells is needed for understanding the correlation between changes in environmental conditions and cell metabolic activity. In this study, Raman spectroscopy combined with deuterium labelling was used to analyze the metabolic activity of a single Escherichia coli O157:H7 cell. The incorporation of deuterium from heavy water into cellular biomolecules resulted in the formation of carbon-deuterium (CD) peaks in the Raman spectra, indicating the cell metabolic activity. The broad vibrational peaks corresponding to CD and CH peaks encompassed different specific shifts of macromolecules such as protein, lipids, and nucleic acid. The utilization of tryptophan and oleic acid by the cell as the sole carbon source led to changes in cell lipid composition, as indicated by new peaks in the second derivative spectra. Thus, the proposed method could semi-quantitatively determine total metabolic activity, macromolecule specific identification, and lipid and protein metabolism in a single cell. [ABSTRACT FROM AUTHOR]

[Display omitted] • THz-TDS technology was used to identify rice grains infested with Sitophilus oryzae at different growth stages. • CDAE was developed to reconstruct preprocessed THz spectra for eliminating noise. • RFC model was constructed to analysis original and reconstructed THz spectra. Rice grains are often infected by Sitophilus oryzae due to improper storage, resulting in quality and quantity losses. The efficacy of terahertz time-domain spectroscopy (THz-TDS) technology in detecting Sitophilus oryzae at different stages of infestation in stored rice was employed in the current research. Terahertz (THz) spectra for rice grains infested by Sitophilus oryzae at different growth stages were acquired. Then, the convolutional denoising autoencoder (CDAE) was used to reconstruct THz spectra to reduce the noise-to-signal ratio. Finally, a random forest classification (RFC) model was developed to identify the infestation levels. Results showed that the RFC model based on the reconstructed second-order derivative spectrum with an accuracy of 84.78%, a specificity of 86.75%, a sensitivity of 86.36% and an F1-score of 85.87% performed better than the original first-order derivative THz spectrum with an accuracy of 89.13%, a specificity of 91.38%, a sensitivity of 88.18% and an F1-score of 89.16%. In addition, the convolutional layers inside the CDAE were visualized using feature maps to explain the improvement in results, illustrating that the CDAE can eliminate noise in the spectral data. Overall, THz spectra reconstructed with the CDAE provided a novel method for effective THz detection of infected grains. [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]

[Display omitted] • A novel label-free fluorescent aptasensor was designed to detect tropomyosin. • DNA-templated copper nanoclusters were synthesized as fluorescent signal. • The aptasensor could achieve high sensitivity and specificity of allergen detection. • The utility of the aptasensor was demonstrated in processed shrimp products. Tropomyosin (TM) is the main allergen in shellfish. Developing a novel, simple and accurate method to track and detect TM in food products is necessary. In this work, a label-free fluorescent aptasensor based on polythymidine (poly(T))-templated copper nanoclusters (CuNCs) was designed for sensitive detection of TM in processed shrimp products. Magnetic beads (MBs), aptamer and cDNA were used to construct an MBs-aptamer@cDNA complex as a detection probe, and with the presence of TM, the poly(T)-templated CuNCs attached at the end of the cDNA as the fluorescent signal was released from the complex to turn on the fluorescence. Under optimal conditions, the poly(T)-templated CuNCs aptasensor achieved a linear range from 0.1 to 50 μg/mL (R2 = 0.9980), a low limit of detection of 0.0489 μg/mL and an excellent recovery percentage of 105.29%-108.91% in the complex food matrix, providing a new approach for food safety assurance. [ABSTRACT FROM AUTHOR]

A cysteamine functionalized core shelled nanoparticles (Au@Ag-CysNPs) was presented for simultaneous and rapid detection of sodium thiocyanate (STC) and benzoic acid (BA) preservatives in liquid milk using surface-enhanced Raman spectroscopy (SERS) technique. A spectrum covering 350–2350 cm−1 region was selected to detect STC with concentrations ranging from 0.5 to 10 mg/L and BA with concentrations ranging from 15 to 240 mg/L in milk samples. Characterization of nanoparticles using high-resolution TEM confirmed that the successful synthesis of Au@AgNPs with core (gold) size of 28 nm and shell (silver) thickness of about 5 nm was grafted with 120 μL of 0.1 nM cysteamine hydrochloride. Results showed that Au@Ag-CysNPs could be used to detect STC up to 0.03 mg/L with a limit of quantification (LOQ) of 0.039 mg/L and a coefficient of determination (R2) of 0.9833 in the milk sample. For detecting BA, it could be screened up to 9.8 mg/L with LOQ of 10.2 mg/L and R2 of 0.9903. The proposed substrate was also highly sensitive and the employed method involved only minor sample pretreatment steps. It is thus hoped that the new substrate could be used in the screening of prohibited chemicals in complex food matrices in future studies. Unlabelled Image • SERS could simultaneously and rapidly screen adulterants in milk. • Cysteamine functionalized core shelled nanoparticles were proposed as substrates. • Benzoic acid was evaluated for the first time in liquid milk using SERS method. • Sodium thiocynate and benzoic acid of up to 0.03 and 9.8 ppm were detected • The proposed method was ecofriendly and easy to follow. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman spectroscopy based on thioglycolic acid (TGA) functionalized silver-coated gold nanoparticles (Au@Ag-TGANPs) was developed for the facile screening of thiabendazole (TBZ) and ferbam (0.025–10 ppm) in liquid milk for the first time. Results showed that silver-coated gold nanoparticles (Au@AgNPs) with a core size of 32 nm and a shell thickness of 5 nm was successfully modified with 3 nm TGA. The sensitive Au@Ag-TGANPs could enhance TBZ and ferbam signals by factors of 6.4 × 104 and 9.8 × 104, respectively, and achieved the detection of TBZ and ferbam with limits of detection of 0.12 and 0.003 ppm, R2 of 0.988 and 0.9821, percent recoveries of 88–103% and of 87.2–103.5%, and relative standard deviations of 4.1–9.2% and 3.5–8.3%, respectively. The current simple and green method could thus be used to detect other unsafe chemicals in future studies. Unlabelled Image • Thioglycolic acid-modified core-shelled NPs were developed as SERS substrate. • Thiabendazole and ferbam was first time reported in milk samples. • The employed method can detect TBZ and ferbam up to 0.12 and 0.003 ppm. • The proposed method needs minor sample pretreatment steps. [ABSTRACT FROM AUTHOR]

Existing approaches for the screening of unsafe materials in food matrices are time-consuming, tiresome and destructive in nature. Therefore, in the current study, a surface-enhanced Raman spectroscopy (SERS) method based on octanethiol-functionalized core-shell nanoparticles (Oct/Au@AgNPs) was established for rapid detection of ziram in apple and pear fruits. The morphology of substrate was evaluated using high-resolution TEM images and superimposed HAADF-STEM-EDS elemental mapping images, which confirmed that Au@AgNPs having gold (Au) core size of 28 nm in diameter and silver (Ag) shell of 5.5 nm in thickness were successfully grafted with octanethiol. The SERS method with the sensitive nanoparticles could detect ziram of up to 0.015 and 0.016 ppm in apple and pear with high coefficients of determination (R2) of 0.9987 and 0.9993, respectively. Furthermore, satisfactory recoveries (80–106%) were also accomplished for the fungicide in real samples. This work demonstrated that the functionalized silver-coated gold nanoparticles were easy to prepare and could be used as sensitive SERS platforms for monitoring of other agrochemicals in foods. Unlabelled Image • Octanethiol functionalized core-shell nanoparticles (Oct/Au@AgNPs) were developed. • Oct/Au@AgNPs were used as SERS substrate for ziram evaluation in fruit extracts. • Oct/Au@AgNPs showed rich hotspots with excellent SERS enhancement and sensitivity. • Oct/Au@AgNPs could be used for monitoring other agrochemicals in foods. [ABSTRACT FROM AUTHOR]