Design Of SERS Microfluidic Chip And Detection Of Rape Residue

Rape contains a variety of nutrients,such as vitamins,minerals and proteins.However,if it is polluted by heavy metals,pesticides,chemical fertilizers and other harmful substances,it will cause harm to human health.Therefore,to ensure the safety of rape is one of the important measures to protect human health.Aiming at such problems as limited detection sensitivity,high time and human cost,non-real-time monitoring and easy interference of detection results by traditional detection methods of rape pesticide residues,a SERS microfluidic chip was designed by combining SERS technology and microfluidic technology to nondestructively detect various pesticide residues in rape,which greatly improved the detection efficiency of rape pesticide residues.The main research contents are as follows:（1）A SERS base based on Raman detection was designed.（1）A variety of self-assembly methods and types of nanospheres were summarized.Polystyrene（PS）microspheres at 200,300,400 and 500nm were selected to realize self-assembly of PS microspheres on silicon substrate by spinning coating method.The hydrophilicity of the surface of the silicon wafer was improved by oxygen plasma treatment,silver nanolayer was magnetron sputtering on the surface of the silicon wafer,and experimental conditions such as the dispersion concentration of PS microspheres,spin coating speed and spin coating time were regulated.Finally,the PS microspheres of four sizes could be self-assembled into a large-scale and highly ordered array structure on the surface of the1.5cm×1.5cm silicon wafer.（2）Using template method as SERS base.The SERS base of Ag-PS microspheres was prepared by magnetron sputtering with different sizes of large scale highly ordered PS microsphere templates.Aiming at the SERS bases of AG-PS balls of different sizes,by exploring their morphology and Raman spectrum,it was confirmed that when the size of PS microsphere was 200nm and the thickness of deposited Ag was 60nm,the SERS bases prepared had the best enhancement effect.The detection range of R6G probe molecules was 10^-2M-10^-12M,and the detection limit was up to 10^-12M.R² was 0.984,and the enhancement factor reached 2.4×10¹⁰ at 1506cm^-1.The uniformity of SERS base was tested,RSD were 14.5%.（3）Graphene oxide was selected to improve the stability of SERS base,namely the antioxidant capacity.On the basis of the prepared Ag-PS microspheres SERS base,the Go-Ag-Ps microspheres SERS base with long-term stability was prepared by rotating coating with GO.The prepared Go-Ag-Ps microspheres were detected in SERS base and Ag-PS microspheres at the same time,and the SERS base spectral intensity protected by GO was slightly reduced.When the two SERS bases were exposed to air for Raman detection at an interval of 5 days,the test intensity of Ag-PS microspheres after 30 days was 65.6%of the initial strength,and that of GO-Ag-PS microspheres after 30 days was 76.6%of the initial strength,which increased the stability by 11%.（2）The electromagnetic field simulation experiment of SERS substrate was carried out.The electromagnetic enhancement principle and FDTD principle of SERS were introduced.FDTD simulation software was used to simulate the electromagnetic field of SERS base,and the optimal theoretical model was obtained.The results show that at785nm wavelength,the enhancement effect of electromagnetic field decreases with the increase of Ag thickness.With the decrease of Ag nanoparticle spacing,the enhancement effect of electromagnetic field is better.That is,when the thickness of Ag was 60nm and the spacing between silver plated PS microspheres was 2nm,the electromagnetic enhancement effect was optimal,which provided theoretical support for the preparation and detection of SERS base.（3）The SERS microfluidic chip was developed.After considering the material of microfluidic chip,the design of microfluidic channel and the overall layout of microfluidic chip,PDMS were selected as the material of microfluidic chip and bonded with glass substrate to form a complete microfluidic chip.Three injection ports were designed to detect a variety of substances at the same time.A snakelike channel is designed to facilitate the mixing of the liquid to be measured.Designed the fishbone type detection area,the detection area is large,convenient detection.The silicon mold of microfluidic chip was prepared by UV lithography,and the PDMS cover with microfluidic channel was prepared by inverted mold method.The glass substrate and PDMS cover sheet were treated by plasma equipment,and the prepared GO-Ag-PS SERS substrate was bonded with microfluidic control.Using the immersion method improved the hydrophilicity of the microfluidic channel,with contact angles from 90。C becomes 30。C.The detection of food dye on the pump-free microfluidic chip showed that the red dye solution could fill the whole microchannel within 56s.The performance test of SERS microfluidic chip showed that the detection limit of R6G was as low as 10^-11M,and there was a good linear relationship between peak intensity and concentration,R²=0.982.The relative standard deviation RSD were 9.27%and 8.95%,respectively,with good uniformity and repeatability.（4）The test of pesticide residues in rape was carried out.Raman spectra of carbendazim and pyridine were collected.The SERS spectrum of the standard solution of carbendazim and rimezine was compared with the common Raman spectrum of the standard solution of carbendazim and rimezine,indicating that under the condition of low solution concentration,SERS technology must be used for detection.SERS microfluidic chips were used to test the sensitivity and uniformity of carbendazim and Ridinium.The detection limits of carbendazim and ridinium were both as low as 0.01mg/L,R² were0.987 and 0.994,and had high uniformity,RSD were 7.65%and 6.83%,respectively.The SERS microfluidic chip designed in this paper met the national requirements for the detection result of pesticide residues in rape,and had high practicability.