Surface-enhanced Raman scattering (SERS) greatly increases the detection sensitivity of Raman scattering. However, its real applications are often degraded due to the unrepeatable preparation of SERS substrates. Herein presented is a very facile and cost-effective method to reproducibly produce a novel type of SERS substrate, a monolayer photonic crystal (PC). With a building block of laboratory-prepared monodisperse SiO2particles deposited with space-tunable silver nanobulges (SiO2@nAg), a PC substrate was first assembled at the air–water interface through needle tip flowing, then transferred onto a silicon slide by a pulling technique. The transferred monolayer PCs were characterized by SEM and AFM to have a hexagonal close-packed lattice. They could increase Raman scattering intensity by up to 2.2 × 107-fold, as tested with p-aminothiophenol. The relative standard deviations were all below 5% among different substrates or among different locations on the same substrate. The excellent reproducibility was ascribed to the highly ordered structure of PCs, while the very high sensitivity was attributed to the strong hotspot effect caused by the appropriately high density of nanobulges deposited on SiO2particles and by a closed lattice. The PC substrates were validated to be applicable to the SERS assay of trace thiol pesticides. Thiram pesticide is an example determined in apple juice samples at a concentration 102-fold lower than the food safety standard of China. This method is extendable to the analysis of other Raman-active thiol chemicals in different samples, and the substrate preparation approach can be modified for the fabrication of more PC substrates from other metallic nanobulge-deposited particles rather than silica only.Keywords:monolayer photonic crystal;silica particles;silver nanobulge deposition;SERS assay;pesticide determination
Ruidong Zhou,Xinyuan Zhang,Yupeng Wen,Wendi Huo,Yingchun Mu,Huan Liu,Chaoying Zhang,Jincheng Li
Multi-walled carbon nanotubes (MWCNTs) are known for their excellent purification properties in QuEChERS-based pesticide analysis, but their potential release and non-recyclability pose environmental and economic challenges. In this study, a novel strategy is proposed to immobilize MWCNTs with chitosan, forming the MWCNTs@chitosan composite, which enables the recyclability of MWCNTs. This composite was employed in a one-step pressure filtration purification method to simultaneously purify extracts of 49 pesticides from aquatic products. Coupled with HPLC-MS/MS, an optimized QuEChERS method was successfully validated for the determination of 49 pesticides. The MWCNTs@chitosan composite demonstrated excellent clean-up capability, effectively removing interfering substances from crude extracts while maintaining recoveries of 71.2–119.4 % and relative standard deviations (RSDs) below 20.0 %. These results demonstrate the composite’s suitability as a QuEChERS cleanup material, with potential applications in other complex matrices.
A simple homogeneous photoelectrochemical (PEC) sensing platform based on an alkaline phosphatase (ALP)–mediated pesticide assay was established for the sensitive detection of omethoate (OM). The Bi 2 S 3 @Bi 2 Sn 2 O 7 heterojunction was used as a photoactive material to provide stable background photocurrent signals. The inhibition of OM on ALP and PEC determination was carried out in the homogeneous system. In the absence of OM, dephosphorylation of L-ascorbic acid 2-phosphate trisodium salt (AAP) was catalyzed by ALP to produce the enzyme-catalyzed product (L-ascorbic acid, AA). AA, as an electron donor, could capture photogenerated holes on the Bi 2 S 3 @Bi 2 Sn 2 O 7 heterojunction, thus inhibiting the recombination of electron holes to achieve an increase of the photocurrent signal. When the OM was introduced, the enzyme activity of ALP was reduced due to the organophosphorus pesticides (OPs)–based enzyme inhibition, and the AA produced by catalytic hydrolysis was also reduced, thus reducing the photocurrent signal. Compared with the traditional PEC sensor for OPs, this homogeneous PEC sensor avoided immobilization procedures, covalent labeling, separation, and the steric hindrance effect caused by immobilized biomolecules, which achieved high recognition efficiency and caused a reduction in analysis time. Additionally, an ALP-mediated pesticide assay for the determination of OPs with a simplified experimental process further improved the stability and reproducibility of the PEC sensor. The PEC sensor showed high sensitivity to the target OM within a dynamic range of 0.05 ~ 500 ng mL −1 , and the detection limit was 0.0146 ng mL −1 . Additionally, the PEC biosensing system showed good selectivity and anti-interference ability, and exhibited a satisfactory result in spinach and mustard samples. Graphical abstract A homogeneous PEC biosensor based on ALP inhibition strategy was constructed for OM detection in vegetable samples via Bi 2 S 3 @Bi 2 Sn 2 O 7 heterojunction as the photoactive substrate material
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