| The emergence of organic pesticides has contributed to the rapid development of contemporary agriculture,but their irrational use has led to an increase in pesticide residues in agricultural products and the environment.Pesticide residues are hard to degrade,bio-concentrate and their migration and transformation in the environment with the food chain and food web eventually pose a threat to human health and ecosystem safety.Traditional monitoring techniques for pesticide residue are complex and time-consuming,therefore it is urgent to develop a rapid detection approach.Surface-enhanced Raman spectroscopy with advantages of high sensitivity and accurate"fingerprint"spectral characteristics has made a series of progresses as a promising technique for pesticide residue detection in recent years.In this study,a composite Ag/Ti O2 surface-enhanced Raman substrates with high sensitivity and photocatalytic properties for pesticide residue detection have been prepared,and the intrinsic correlation between their morphological structure and microscopic properties and Surface-enhanced Raman scattering(SERS)was explored,furthermore the application in the rapid detection of agricultural products was discussed.The main research components are the following.(1)Preparation of Ag/Ti O2 substrates and optimization of their SERS performanceThe effect of calcination temperature on crystalline shape of Ti O2 was investigated,and Ag nanoparticles were electrodeposited on Ti O2 films to prepare the composite Ag/Ti O2 SERS substrates.The Ag nanoparticle morphology was regulated by changing the electrochemical deposition conditions,and then its effect on the SERS performance of the substrates was investigated to determine the optimal parameters.The final determination parameters is as follows:the calcination temperature of Ti O2 is 500°C;the concentration of Ag NO3 electrolyte was 0.01 m M;the external voltage was 20 V and the reaction time was 40 min.(2)Study of photocatalytic properties of Ag/Ti O2 composite substratesThe properties of Ag/Ti O2 composite substrate,such as homogeneity,and photocatalytic properties,were investigated using the rhodamine 6G as the probe molecule.The results showed that the Ag/Ti O2 composite substrate had a strong enhancement effect with an enhancement factor of 1.23×1012,and the substrate had high reproducibility and stability to maintain stable SERS performance within 45 days,in addition to its good self-cleaning properties,the substrate can be reused more than three times.(3)Application of Ag/Ti O2 composite SERS substrate in pesticide residue detectionThe Ag/Ti O2 composite SERS substrate prepared above was applied to simulate the detection of glyphosate agrochemical residues on plant leaves.Firstly,the SERS spectra of standard solutions with different concentrations of glyphosate were tested.The results showed that the concentration of glyphosate standard solution was exponentially related to its Raman intensity at 521 cm-1 in the Raman spectrum,in which the Raman peak intensity was the strongest overall at 0.01 ppm of glyphosate,and obvious glyphosate Raman characteristic peaks could still be detected at concentrations as low as 0.1 ppb.Next,the self-cleaning effect of the substrate on glyphosate molecules was investigated,and the results showed that 0.1 ppm of glyphosate on the substrate was completely degraded after 4 min of UV light.Finally,the pesticide spraying was simulated on plant leaves,and then the pesticide residues on the surface of the vegetables were eluted by deionized water onto Ag/Ti O2 composite SERS substrate for Raman testing.The results showed that the substrates could achieve the residue simulation detection of glyphosate concentration of 0.1 ppm sprayed on plant leaves. |
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