Controllable Preparation Of Silver Colloid SERS Substrate And Application In Pesticide Residue Detection

Pesticides are important to protect crops and reduce yield loss.However,the overuse of pesticides leads to excessive pesticide residues in agricultural products,which will threaten human health and cause environmental pollution.Therefore,the rapid,accurate and low-cost detection of pesticide residues is of great significance.The commonly used chromatographic method detection result is reliable,but it has disadvantages of high cost,tedious pretreatment process and long detection time.Surface-enhanced Raman spectroscopy(SERS)developed rapidly in pesticide residue detection due to its high sensitivity and rapid non-destructive testing.In this paper,in order to realize the reliable qualitative and quantitative analysis of dithiocarbomates(DTCs)pesticides,amobam,metiram and mancozeb belong to ethylene-bis-dithiocarbamates(EBDCs)type of DTCs were selected as the analyte.The silver colloid SERS substrate with quasi-spherical,controllable particle size and good repeatability was synthesized and successfully applied to detect the three pesticides.The main research contents and conclusions are as follows:(1)The nano-silver colloid was prepared by the one-pot method using sodium citrate and ascorbic acid(AA)as reducing agents.The silver nanoparticles(Ag NPs)are quasi-spherical with uniform particle size.The silver colloid has good SERS enhancement effect and can be used as a substrate.(2)The controllable preparation of average particle size in the range of 49-113 nm was achieved by adjusting reductant concentration,reaction temperature,reaction time and AA addition rate.The enhancement effect of SERS is obviously affected by the particle size.The best SERS signal was obtained from the Ag NPs with a particle size of 70.65 nm for amobam,metiram and mancozeb.The silver colloid with this reaction condition was used as SERS substrates for subsequent detection.(3)The relative standard deviation(RSD)of peak intensity was used to estimate the reproducibility of SERS signal.The RSD of silver colloid prepared by this method is less than 5% for the same batch,and less than 10% for the different batches.The average particle size of different batches is 72.16±4 nm.The repeatability is much better than that of silver colloid obtained by traditional Lee-Meisel method.The effects of adding order of pesticides,regulator types and detection time on the SERS signals of amobam,metiram and mancozeb standard aqueous solution were studied.The RSD of SERS signals of three pesticides is less than 5%,which meets the requirements of quantitative analysis.(4)The SERS spectra of metiram and mancozeb are similar.Soft independent modeling of class analogy method(SIMCA)is used to realize qualitative discrimination of the two pesticides.By adjusting the volume ratio of silver sol to pesticide,the limit of detection(LOD)of amobam,metiram and mancozeb is 0.01 ppm,0.02 ppm and 0.01 ppm,respectively.All of them are lower than the maximum residue limit(MRL)required in the national standard GB 2763-2019.The SERS detection of amobam and metiram was studied for the first time,and the LOD of mancozeb is lower than the reported at present.Without complex sample processing and data processing,the quantitative analysis of amobam,metiram and mancozeb pesticide residues is realized in a wide concentration range.The linear range of amobam is 0.01-0.3 ppm and 0.3-50 ppm,metiram is 0.03-50 ppm,mancozeb is 0.1-10 ppm.The recovery is between 75% and 110%.The limit of quantitation(LOQ)of amobam,metiram and mancozeb in grape juice is 1 ppm,0.5 ppm and 0.5 ppm,respectively.All of them are lower than the MRL of grape required in the national standard GB2763-2019(5 mg/kg).These results indicate that the substrate has good application potential.