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Developing simple, efficient, and inexpensive method for trace amount organophosphorus pesticides' (OPs) detection with high sensitivity and specificity is of significant importance for guaranteeing food safety. Herein, an Ag/Au bimetallic nanoparticle-based acetylcholinesterase (AChE) surface-enhanced Raman scattering (SERS) biosensor was constructed for in situ simple and sensitive detection of pesticide residues in food. The principle of this biosensor exploited 4-mercaptophenylboronic acid (4-MPBA)-modified Ag/Au bimetallic nanoprobes as SERS signal probe to improve sensitivity and stability. The combination of AChE and choline oxidase (CHO) can hydrolyze acetylcholine (ATCh) to generate H2O2. The product of H2O2 selectively oxidizes the boronate ester of 4-MPBA, decreasing the Raman intensity of the B-O symmetric stretching. In the presence of OPs, it could inhibit the production of H2O2 by destroying the AChE activity, so the reduction of the SERS signal was also alleviated. Based on the principle, an Ag/Au bimetallic nanoparticle-based AChE SERS sensor was established without any complicated pretreatments. Benefiting from the synergistic effects of Ag/Au bimetallic hybrids, a linear detection range from 5×10−9 to 5×10−4 M was achieved with a limit of detection down to 1.7×10−9 M using parathion-methyl (PM) as the representative model of OPs. Moreover, the SERS biosensor uses readily available reagents and is simple to implement. Importantly, the proposed SERS biosensor was used to quantitatively analyze OP residues in apple peels. The levels of OPs detected in real samples by this method were consistent with those obtained using gas chromatography–mass spectrometry (GC–MS), suggesting the proposed assay has great potential applications for OPs in situ detection in food safety fields. [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]

• PDADMAC/PSS/Au@Ag NRs filter paper is a kind of disposable environment-friendly flexible SERS substrate. • The PDADMAC/PSS modified filter paper showed the potential of SERS substrate for nanoparticle self-assembly. • The prepared paper-based SERS substrate had high SERS activity and good reproducibility. • PDADMAC/PSS/Au@Ag NRs filter paper realized the "paste-reading" detection of MP, TMTD and CPF on the pericarp. The goal of food safety supervision is to directly identify the pesticide residues on the surface of fruits and vegetables. This study proposed to develop a facile, non-destructive, and sensitive method based on surface-enhanced Raman scattering (SERS) to detect non-systemic pesticides on the surface of fruits and vegetables. The composite material was prepared by loading CTAB guided Au@Ag NRs with positive charge onto filter paper which was modified with PDADMAC(+) and PSS(−) using electrostatic adsorption. Au@Ag NRs with bimetallic synergies were effectively adsorbed in the fiber grid to generate 3D SERS hotspots within a few microns of depth. The results showed that the 3D composite flexible substrate had a high SERS activity, great repeatability, and sensitivity when the method was utilized to detect 4-MBA, methyl-parathion, thiram and chlorpyrifos. Three kinds of non-systemic pesticides on the peel could be detected directly and quickly owing to the arbitrary bending of the substrate, demonstrating the efficiency of the SERS "paste-reading" method. The acquired findings demonstrated that PDADMAC/PSS/Au@Ag NRs composite filter paper had the potential to provide rapid feedback for in- situ analysis of pesticide residues on the surface of fruit and vegetable. [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]

An essential aspect for the wide practical application of surface-enhanced Raman spectroscopy (SERS) lies in the further improvement of its sensitivity. In this paper, a strengthened chemical effect with a high enhancement factor (EF) of 3.9 × 107 was first triggered through simply adjusting the heterojunction structure between graphitic carbon nitride (g-C 3 N 4) flake and molybdenum disulfide (MoS 2) nanoflower. Ag nanoparticles (Ag NPs) were then photo-reduced onto the g-C 3 N 4 @MoS 2 matrix to introduce significant steric electromagnetic field under excitation, which was further reinforced by provoking a resonance coupling effect based on graphene oxide (GO) resonant cavity. Such a cavity was set between the g-C 3 N 4 @MoS 2 @Ag-polydimethylsiloxane (PDMS) matrix and the Ag nanocubes (Ag NCs)-embedded PDMS coating membrane, facilitating a robust flexible SERS chip with a promising EF attained as 1.1 × 109. Additionally, the SERS intensity was only decreased by 5% after three months, indicating the excellent stability of the as-prepared bilayer SERS chip. The on-site reclaimable monitoring for thiram (TMTD) and methyl parathion (MP) accompanied by a low limit of detection (LOD) of 10−6 mg/mL was achieved by utilizing the proposed sophisticated SERS chip, demonstrating its fascinating application feasibility. [Display omitted] • A structure-ameliorated chemical enhancement was triggered by the heterojunction of g-C 3 N 4 flake and MoS 2 nanoflower. • A remarkable electromagnetic resonant effect with a high EF of 1.1 × 109 was facilitated by nanoscale GO resonant cavity. • The versatile bilayer membrane chip demonstrated an on-site reclaimable monitoring of pesticides with a LOD of 10−6 mg/mL. [ABSTRACT FROM AUTHOR]