Preparation Of Paper SERS Substrate And Its Application In The Detection Of Pesticide Residues In Fruits

The pesticides can effectively improve the yield and quality of agricultural products.However,the abuse of the pesticides can give rise to direct harm to human beings,animals and the environment.Therefore,it is necessary to strictly detect pesticide residues.At present,various analytical methods have been used to detect pesticide residue,such as gas chromatography,high performance liquid chromatography,liquid chromatography and enzyme inhibition.Surface enhanced Raman scattering（SERS）spectroscopy is an advanced surface analysis technique,which can greatly improve the Raman scattering signal of molecules adsorbed on some rough metal surface.The key of SERS technique in pesticide residue detection is to prepare high sensitivity,good uniformity,repeatable and stable active substrates1.The AgNPs/paper substrates were fabricated by inkjet printing silver nanoparticles inks on papers（photographic,graph,weighing and printing paper）with different wettability.The effect of excitation wavelength on SERS signal and the influence of drying temperature on SERS substrates activities were systematically discussed.The scanning electron microscope equipped with an in-lens detector was used to determine the surface morphologies of the papers before and after inkjet printing.The measurement of contact angle was used to evaluate the wettability of the surface.Probe molecule,thiram solution,was used to evaluate the SERS performance of the AgNPs/paper substrates,such as sensitivity,uniformity,repeatability and stability.The SERS measurement were obtained by using a high-resolution Raman microscope The lowest detection concentration of thiram solution for AgNPs/photographic paper which exhibited highest SERS enhancement was 10^-10 mol/L.Good linear response between the SERS intensities and logarithmic concentrations was obtained from 10^-4-10^-10 mol/L（R²=0.9932）.And the AgNPs/photographic paper had good uniformity and reproducibility with relative standard deviation values less than 5%measured by eight points and ten substrates,respectively.In addition,the AgNPs/photographic paper showed good stability within eight months.2.The AgNPs/photographic paper substrate were prepared by using automatic writing method.The lowest concentration of thiram for the SERS substrate was detected to evaluate the sensitivity.The relative standard deviations of Raman characteristic peaks,which were collected from 20 points and 10 substrates,were calculated to characterize the uniformity and repeatability of the substrates.The activity of SERS substrate stored in different time was tracked to analyse the stability.3.AgNPs/photographic paper was used to detect thiram residues in fruit juice and juice.The residual states of thiram were dropped on the surface of fruit and mixed in fruit juice to simulate.The probe was adsorbed on the surface of SERS substrate by wiping or micro titration.The lowest detection concentration of thiram mixed in fruit juice and on the surface of fruit peel were 0.024 ppm,0.25 ng/cm².The uniformity of the substrate applied to thiram residue detection were measured by randomly select 10 points from the substrates.The relative standard deviation of the characteristic peaks were less than 10%,showing good uniformity.Therefore,AgNPs/photographic paper has application potential in the detection of pesticide residues.