Study On The Detection Of Pesticide And Veterinary Drug Residues By Surface-enhanced Raman Scattering Based On Different Active Substrates

Ciprofloxacin,oxytetracycline and amitraz are three commonly used veterinary drugs which have a broad-spectrum of antibacterial properties,and were widely used in animal disease prevention and treatment in livestock and aquaculture.However,the excessive use of them easily leads to residues,that brings about serious poisonous effect on animal and human health.So it is of great significance to establish a convenient,rapid and sensitive method for the analysis and detection of veterinary drugs residues in order to ensure the safety of food quality and human health in China.Surface-enhanced Raman scattering(SERS)is a new spectral analysis technique based on Raman spectroscopy and the specially optical phenomenon of metal nanoparticals which can give us the fingerprint spectrum of molecular.SERS is being applied extensively in the determination of antibiotics and other veterinary drugs for the advantages of high sensitivity,quick analysis and easy operation.The main purpose of this study was to develop a rapid and efficient method for the detection of ciprofloxacin,oxytetracycline and amitraz by using SERS technology and synthesis of Nano-active Substrates.The content manily involves:Au naoparticles?Ag naoparticles?Ag colloid films and Au@Ag core-shell bimetallic nanoparticles with high SERS activity were prepared by chemical reduction and self-assembly method.The structure and morphology were characterized by UV-Vis?EDX?TEM and SEM.The best three-dimensional molecular configurations of three veterinary drugs were simulated and their theoretical Raman spectra were calculated by density functional theory(DFT).The theoretical Raman spectra were compared with the normal Raman spectra(NRS)of them,and the vibration assignments of main peaks were identified.Ag nanoparticles were used as SERS active substrate to enhance the Raman signals of ciprofloxacin.The results showed that the SERS signal response had excellent performance when the volume ratio of ciprofloxacin to Ag colloid was 20:10,the concentration of sodium chloride was 80 mmol/L and the mixing time for 30 min.Under the optimum conditions,a good linear relationship between the SERS intensity and the concentration of ciprofloxacin in the range of 0.1~4 ?g/mL was obtatined and the detection limit was calculated as 0.083 ?g/mL.At last,the ciprofloxacin concentration in water samples was also analyzed and the recoveries were in the range of 82.0~100.4% with the relative standard deviation(RSD)?6.12%.Oxytetracycline often displays low SERS signal on the Ag nanoparticles,so Ag colloid films were prepared and to be as SERS active substrate and were used to increase the Raman signals of oxytetracycline.The optimum SERS enhancement effect of Ag colloid film was presented when the Ag colloid pH was 6 and the self-assembly time was 6 h.Under the optimum conditions a good linear relationship was obtained between the SERS intensity and the concentration of oxytetracycline in the range of 0.08~2 ?g/mL and the detection limit was calculated as 0.068 ?g/mL.At last,the concentration of oxytetracycline in water samples was also analyzed and the recoveries were in the range of 79.5~94.9% with the RSD of 3.60~5.75%.Finally,the core-shell structure of Au@Ag bimetallic nanoparticles were used as SERS active to study amitraz.The thickness of the coated Ag shell is regulated by changing the Ag/Au molar ratios in the preparation solution,which lead to the changing of the SERS activity of Au@Ag nanoparticles.The results showed that the optimum SERS activity appeared when the Ag/Au molar ratio is 6:5 and the thickness of Ag shell is 6 nm.Moreover,the SERS effect of Au@Ag nanoparticles was obviously stronger than that of pure Au or Ag nanoparticles.The factors influencing the SERS intensity of amitraz were further investigated and the results showed that the SERS signal response had excellent performance when the ethanol was served as solvent,volume ratio of Au@Ag nanoparticles to amitrazto was 20:10 and the concentration of sodium chloride was 25 mmol/L.Under the optimum conditions,the concentration of amitraz presented a good linearship with the SERS intensity in range of 0.977~29.3 ?g/mL,and the detection limit was 0.66 ?g/mL.At last,the recoveries of amitraz in milk were detected between 81.7% and 100.5% with the RSD of 2.61~5.51%.The results were satisfactory and provided a new analytical method for the detection of amitraz.