Study On Construction And Performances Of SERS Sensors For Methyl Parathion And Melamine

With the improvement of people's living standards,more and more attentions have been paid to the monitoring of organic pollutants in food and environment.The traditional chromatographic detection methods inevitably have the defects of high cost,complex sample processing and long time consuming.Since the discovery of Surface Enhanced Raman Spectroscopy?SERS?,it has been widely used in analytical chemistry.SERS detection technology is based on the molecular vibration spectrum of the target molecule,which produces a specific fingerprint for a given molecule,so it has strong anti-interference ability.Compared with the traditional chromatographic detection technology,the portable Raman spectrometer can also be used to detect organic pollutants quickly,so SERS detection has the advantages of portability,easy operation,low cost and fast analysis.In this study,several solid/liquid SERS sensors based on gold and silver nanostructural materials were constructed for the detection of methyl parathion?organophosphorus pesticides?and melamine?illegal food additives?in food and environment.The main works in this study are summarized as follows:?1?Four solid-state SERS sensors with quasi-three-dimensional noble metal nano-film structure were fabricated by“electrospinning-high-temperature calcination”two-step route and used for the detection of methyl parathion and melamine.Using HAuCl₄/PVP,AgNO₃/PVP and AgNO₃/Ni?NO₃?₂/PVP as precursors,nanofibers were prepared by electrospinning and calcined at high temperature to form four quasi-three-dimensional nanomembranes:AuNM,AgNM1,AgNM2 and Ag-NiO nanofiber membranes?Ag-NiO NFs?.Four kinds of SERS substrates were characterized using FT-IR and XRD.The enhancement factors of four SERS substrates were 5.6×10⁴,8.4×10⁴,1.4×10⁵ and 2.4×10⁴,respectively.The test results showed that the detection limits of AuNM and Ag-NiO NFs to methyl parathion was less than 10?M,and that of AgNM1 and AgNM2 to melamine was less than 2.5?M.The study shows that the two-step method of“electrospinning-high temperature calcination”provides a new way to fabricate high performance SERS sensors.?2?In order to reduce the fabrication cost of solid SERS substrate and improve its detection sensitivity,a hydrophobic multi-hotspot solid-state SERS sensing platform with wax/AuNPs-analyte/AuNPs?W/Au-A/Au?structure was constructed for the detection of methyl parathion and melamine in solution.Five different sizes of AuNPs were synthesized by Frens'method and characterized by UV-vis,TEM and XRD.The experimental results show that ANPs with sizes of 60 nm and 130 nm have the best SERS effect on methyl parathion and melamine,respectively.The SERS sensing platform with AuNPs-analyte/AuNP?W/Au-A/Au?structure was constructed on hydrophobic wax-coated silicon.The detection limits of methyl parathion and melamine were less than 10nM and 1nM respectively.The high sensitivity of SERS sensor with hydrophobic multi-hotspot structure is proved by experiment and simulation of the surface electric field of AuNPs using finite element method.?3?For the goal of quantitative analysis of the target in solution,silver nanostructures based SERS sensor were in-situ formed on the surface of copper foil by current substitution deposition for the detection of methyl parathion.The"dendritic"Ag nanostructure SERS substrate was synthesized by optimizing the concentration of AgNO₃.Semi-quantitative analysis of methyl parathion was obtained with practical limits of 1?M.The SERS substrate of silver nanoparticles?AgNPs?was obtained by adding appropriate template polyvinylpyrrolidone?PVP?,with the SERS enhancement factor of 3.6×10⁶.AgNPs based SERS substrate showed good quantitative detection ability towards methyl parathion in the concentration range of 1 to 100?M,with practical detection limit of 1?M.The AgNPs SERS sensor has good repeatability,and the relative standard deviation is 10.27%.The recovery of methyl parathion in lake water was 93.25-112.06%.The relative standard deviation is less than 12%.The results show that the SERS sensor has potential real application values in the quantitative detection of methyl parathion.?4?Three special shape AuNPs colloid SERS sensors were constructed to realize the quantitative detection of methyl parathion.Two kinds of urchin-like AuNPs?S-AuNPs1,S-AuNPs2?and a triangular AuNPs?T-AuNPs?were synthesized by seed growth method and characterized by TEM and XRD.The SERS enhancement factors of the three AuNPs colloids were 1.0×10⁴,1.8×10⁴ and 1.4×10⁴ respectively,which proved their good SERS effect.Three AuNPs colloidal SERS sensors have linear detection ranges of 1-100?M,0.5-100?M and 0.5-50?M,respectively,with pratical detection limits of 1,0.5 and 0.5?M respectively.The recovery rate of methyl parathion in lake water was 94.4-109.1%.The results show that the three AuNPs colloidal SERS sensors are feasible for the effective quantitative detection of target molecules in solution.?5?In order to quantitatively detect the target on the surface of real samples,a Bipyramid AuNPs?BP-AuNPs?based tape SERS sensor was constructed to detect methyl parathion on the surface of vegetables and fruits.BP-AuNPs were synthesized by seed growth method and characterized by TEM,SAED,UV-vis and XRD.The maximum theoretical SERS enhancement factor 1.54×10⁸ was calculated by the discrete dipole approximation method.The BP-AuNPs tape sensor was used to detect R6G and CV on the surface of silicon wafer?simulated real sample?.The practical detection limits were 0.22?g/cm² and 0.1?g/cm²,respectively,which proved the feasibility of the BP-AuNPs-based SERS sensor.The BP-AuNPs tape SERS sensor was used to detect methyl parathion on the surface of lake water samples,vegetables and fruits.The results showed that the detection limit of methyl parathion were 0.8?M in lake water samples and at ng/cm² level in vegetable and fruits samples,which demonstrated the BP-AuNPs tape SERS sensor's practical application value.?6?Based on gold nanorods?AuNRs?colloidal SERS sensor,a“titration-detection”method was established to quantitatively detect methyl parathion on the surface of real samples.AuNRs was synthesized by seed growing method and characterized by TEM,UV-vis and XRD.The linear range of AuNRs colloidal SERS sensor for quantitative analysis of methyl parathion in solution is 1 to 800?M,and the practical detection limit is 1?M.The“titration-detection”method has realized the quantitative detection of methyl parathion on the surface of silicon wafer?simulated solid target surface?.The detection linear range is 90 ng/cm²-10.96?g/cm²;and the detection limit is 90 ng/cm².The SERS sensor is further applied to the detection of methyl parathion contaminated samples.The detection limit in lake water was 1?M,the detection limit on the surface of fruit and plant leaves was ranged from 110 to 440ng/cm²,and the recoveries rate were 96.36-106.02%.Meanwhile,the enhancement of electromagnetic field on AuNRs surface is simulated by finite element method,and the reason of SERS effect is explained,which provides a theoretical basis for the construction of AuNRs-based SERS sensor.The research results prove the potential application of the AuNRs colloidal SERS sensor for the detection of real samples.