Research On Fast Detection Of Glyphosate Residues Based On Molecular Imprinting-surface Enhanced Raman Scattering

Glyphosate is a non-selective,biocidal herbicide.The deposition of glyphosate and its derivatives in raw waters causes widespread pollution.Long-term exposure to glyphosate can cause a variety of human health hazards.Due to its strong polarity,easy ionization in water,easy formation of complexes with metal ions,and the absence of chromophores and fluorophores in its chemical structure,glyphosate residue extraction and quantitative analysis in the complex matrix are restricted.Surface-enhanced Raman spectroscopy(SERS)detection technology has the advantages of ultra-high sensitivity,fast spectrum acquisition,together with real-time and on-site detection.It has gradually applied to the detection of various pesticide residues;however,using SERS for glyphosate determination,the existing detection methods are few in amount and bearing some drawbacks.The matrix interference effect severely restricts the application of SERS in pesticide residues.Using molecular imprinting technology to identify targets specially,the combination of molecular imprinting and SERS technology(MIP-SERS)can achieve specificity identification and high-sensitivity detection for targets in complex matrices.This article aims to develop the MIP-SERS detection system for specific,sensitive,convenient,and efficient detection of glyphosate pesticide residues in complex matrices.The main research contents and results of this article are as follows:(1)Glyphosate can inhibit tyrosinase activity,use SERS technology to detect content of levodopa,which is the substrate of tyrosinase in the glyphosate-added system,and use levodopa as the signal probe to quantify glyphosate.The effects of nano-gold SERS substrates with different ascorbic acid reducing agent dosages and different types of coagulants on the detection signal of levodopa SERS were screened.By optimizing the detection system buffer conditions,enzyme and substrate concentration,incubation temperature and time,and other conditions,the most suitable glyphosate detection conditions were obtained.Under the best detection experimental conditions,the linear range of the detection method for glyphosate is between 100?g L^-1 and 10 mg L^-1(R²=0.988),and the LOD and LOQ of the detection method are 50?g L^-1 and 100?g L^-1,respectively.The advanced detection method has good interference ability to the structural analogs of glyphosate.The recovery rate of the three additional levels is between86.2%and 110.7%,and the RSD is between 6.7 and 11.8%.The obtained results are consistent with those of the LC-MS/MS methods,and can successfully applied to the detection of glyphosate in tap water.The SERS detection method can complete the detection of glyphosate content in water samples within 10minutes.(2)A glyphosate SERS detection method was developed based on binding nanozyme inhibitors.Glyphosate and Cu²⁺can be combined with cysteine to partially alleviate the inhibitory effect of cysteine on the catalytic performance of Au-Pt nanozymes.Chain-shaped Au-Ag composite nanomaterials were prepared to detect the SERS signal of ox TMB,the product of TMB catalyzed by Au-Pt nanozymes.The SERS signal of ox TMB can be used to quantify content of glyphosate.Conditions in the detection system,including the concentration of cysteine and Cu²⁺,the buffer conditions required by the reaction system,and the incubation conditions,have been optimized.Under optimal conditions,the linear range of the detection method for glyphosate is between 10?g L^-1 and 1000 mg L^-1(R²=0.995),and the LOD and LOQ of the detection method are 5?g L^-1 and 10?g L^-1,respectively.The advanced detection method has excellent anti-interference ability against selected metal cations,structural analogs,pesticides,and amino acids.The recovery rate of this method applied to tap water samples is between 92.8%and 106.3%,and the RSD is between 1.9 and 3.3%.(3)To precisely extract glyphosate from a complex matrix,the glyphosate molecularly imprinted polymer was prepared by a sol-gel method,and the types of monomers and the ratio of monomers,templates,and crosslinkers in the polymer preparation process have been optimized.The prepared glyphosate molecularly imprinted polymer materials have high binding efficiency with the target glyphosate and can reach the adsorption equilibrium within 5 minutes.Its maximum adsorption capacity is 39.5?g mg^-1.The kinetic adsorption process of the glyphosate sol-gel molecularly imprinted polymers conforms to the quasi-second-order reaction kinetic model,and its static adsorption process conform to the Langmuir monolayer adsorption characteristics.According to the Scatchard equation analysis,there are two kinds of binding sites with different affinities distributed on the glyphosate sol-gel molecular imprinted polymers.The prepared glyphosate sol-gel molecularly imprinted polymer packed into a sub-imprinted solid-phase extraction column,and its loading,drip washing,and elution conditions were optimized.In tandem with the developed SERS detection method to detect glyphosate in tea,the recovery rate of the three additional levels is between 77.2%and 82.3%,and the RSD is between 5.7 and 10.3%.The results are well consistent with those obtained by LC-MS/MS.The developed MIP-SERS detection system can meet the high specificity and high sensitivity detection requirements of glyphosate in complex matrices.