Analyses Of Flusilazole And Malachite Green In Food By Surface-enhanced Raman Spectroscopy Coupled With Two Silver Composite Substrates

Surface-enhanced Raman spectroscopy technology is an emerging analytical technology,which has been widely used in biomedical,chemical and other fields in recent years due to its high sensitivity to sample analysis,short detection time and small sample size.At the same time,the preparation of SERS substrate has become a hot pot in this area.Two kinds of silver composite substrates were synthesized in this study,the effect of sample pretreatment on the detection of flusilazole in pear was investigated,and SERS technology coupled with stoichiometry was used to explore the qualitative and quantitative possibility for the analyses of flusilazole in pear and malachite green residues in tilapia.Firstly,Au seed and copper nanowires were synthesized by reducing hydrogen chloroauric acid with trisodium citrate and hydrothermal reduction method,respectively.In this paper,two kinds of silver composite materials were prepared by seed growth method:gold-silver core-shell particles?Au@Ag?and silver-coated copper nanowires?Cu-Ag?.The optical characteristics of gold colloids and three different Au@Ag NPs were performed on ultraviolet-visible?UV-Vis?absorbance spectroscopy.The sizes and shapes of the Au@Ag NPs were characterized with a transmission electron microscopy?TEM?.The results indicated that the sizes of Au@Ag NPs were decreased with the increase of Au seed amount and that the average diameters of the three substrates were 98±6,90±7 and 65±4 nm.Secondly,three different diameters of Au@Ag NPs were mixed with the concentration of 1 mg/L and 0.1 mg/L flusilazole standard solutions to select the best SERS substrate for analyzing flusilazole.The results showed that when the amount of Au seeds is 0.5 mL and silver nitrate is 2.7 mL?the Au@Ag NPs size is 90±7 nm?showed the highest enhancement effect and the minimum detectable concentration was 0.1 mg/L.The experimental results indicated a good linear relationship between the Raman intensities of chief peaks and the concentrations of flusilazole solutions?R²=0.924-0.962?.The component of the pear is very complex,so flusilazole can not be detected without pretreatment,which is a necessary step.The pretreatment method of flusilazole was optimized and adjusted according to the national standard method and the QuEChERS method.Adsorbent was added to remove some non-targeted compounds and to reduce the the matrix interference,so the addition of adsorbents was the most important step to remove non-targeted components.Good SERS enhancement would not be obtained when the amount of adsorbent was too little or much.The amount of each absorber dosage was determined(0.6 g MgSO₄,0.2 g C₁₈and 0.2 g PSA)according to several experiments'results.Flusilazole in pear could be identified at as low as 0.1?g/g.The linear relationship between the intensity of prominent peaks and the concentration of pears extracts was not good as flusilazole standard solutions?R²=0.708-0.922?due to the interference of pear matrix.The good linear relationship was acquired at the peak of 632,829,1103 cm^-1?R²>0.9?.The experiment showed that SERS has high sensitivity in pesticide residue analysis and could be used for pesticide safety supervision.Next,two kinds of silver composite materials were applied for detecting the malachite green.A series of Au@Ag and Cu-Ag were synthesized by adjusting the amount of Au seed,copper nanowire and silver nitrate.Two kinds of silver composite substrate were mixed with malachite green standard solution?10?g/L?to find the best SERS substrate for analyzing malachite green.And the result showed that the best conditions for the synthesis of Au@Ag and Cu-Ag reaction conditions were:3 mL Au seeds with 0.9 mL silver nitrate and 0.5 mL copper nanowire with 2.7 mL silver nitrate,respectively.Both these two kinds of silver composite substrate showed the highest enhancement effect on malachite green and the minimum detectable concentration was 0.1 ng/mL and 0.5 ng/mL,respectively.The PLS models were built to evaluate the performance of the quantitative ability of SERS?the R² of PLS models were 0.97 and 0.95,respectively?.The PLS model result indicated that both Au@Ag and Cu-Ag have great potential to detect malachite green standard solution.Cu-Ag substrate,which could be used to detect malachite green extracts from Tilapia at at 1ng/g,is more suitable for malachite green detection and analysis.The PLS model showed great predictability?R²=0.95,RPD=6.171,RMSE=0.595 ng/g?,which indicated that SERS has great potential to be applied in determination of toxic residues in food.This paper provides a kind of efficient and convenient sample pre-treatment methods for pesticide,establishes a SERS quantitative model of flusilazole or malachite green,and also provides great practical potential for simple,rapid and efficient detection of other harmful materials in food.