| The application of pesticides is the most common and effective method used to ensure that the vegetation in municipal landscapes,fruits,and vegetables are protected from pests and diseases.However,the large-scale use of pesticides can easily cause excessive residues of pesticides in water,soil and agricultural products,which seriously endangers environmental safety and human health.But the current pesticide detection technology often relies on large-scale equipment and requires complicated pre-treatment processes,which cannot meet the needs of rapid non-destructive detection of pesticide pollutants.Based on this,it is urgent to establish a non-destructive,rapid and sensitive method for analyzing pesticide pollutants.Surface-enhanced Raman scattering(SERS)technology has the advantages of excellent non-destructive detection,high analytical sensitivity,and short detection time,which makes it an effective method for rapid analysis and detection of trace pollutants.As an indispensable and important part of this technology,the development of functional SERS substrates is of great significance to promote the practical application of SERS technology.Among them,the flexible SERS substrates have the characteristics of deformability,they can be highly suitable for sampling of pollutants with different shapes and roughness surfaces,which show a broad application prospect in the field of non-destructive,sensitive,fast and on-site detection of pesticide pollutants.At present,most of the research on flexible SERS substrate are focused on the realization of high sensitivity,while the researches on other technical difficulties that hinder its application in practical industry/commerce(such as:simple,low-cost,large-area synthesis new strategy;the improvement of pollutant collection rate in the sampling process;bifunctional substrate for both solid and liquid detection,etc.)are relatively lacking.Based on this,several flexible SERS substrates were prepared with PDMS as the main material in this work,and systematic research was carried out from the aspects of the synthesis strategy,versatility,stability,and sampling recovery efficiency of the flexible SERS substrate.The concrete research content and the result brief elaboration are as follows:(1)A new one-step synthesis strategy for preparing PDMS deformable gelled SERS substrates was proposed for the first time,which greatly simplified the traditional PDMS-SERS substrate preparation process.By adding Ag NPs before the PDMS cross-linking reaction,PDMS directly completes the Ag NPs loading uniformly into the gel during the process of cross-linking.The gel SERS substrate has good rheological properties,and it can adapt to sampling of contaminated surfaces with different roughness and topography.By adjusting the preparation conditions,the effects of different reaction conditions on the fluidity,viscoelasticity,and signal sensitivity of the material were all system studied.Under the optimal conditions,R6G was used as a probe molecule,and the detection limit of R6G was as low as0.5 femtomole.Glass slide and sandpaper were used to simulate smooth and rough surface environments,respectively.R6G,thiram,and triazophos on the surface of smooth and rough environment were detected,the minimum detection concentration of R6G on the smooth surfaces was 50 p M,and The minimum detection concentrations of R6G,thiram,and triazophos on the rough surface were 100 p M,0.1 ppm,and 0.1 ppm,respectively.(2)This work proposes a synthesis strategy for flexible PDMS-SERS film-like substrates with rough surfaces using sandpaper as a template.This synthesis strategy solves the problem that the two-dimensional flexible SERS substrate cannot be prepared in a large area and at low cost,and its single preparation area reaches 154 cm~2.In this study,the reaction conditions,such as curing time,the mesh of sandpaper used,and the number of Ag NPs loading layers,were systematically optimized during the preparation of the substrate.Under the optimal conditions,the detection limit of R6G was as low as 4 femtomole.Randomly select points by parallel sampling of SERS substrates with different areas,and tensile strength tests,confirming the reliability of the reliability of the technology in the large-area preparation of the substrate and the stability of the SERS signal in each part of the flexible SERS substrate film.Glass slide was used to simulate a solid surface,and triazophos and methyl parathion on the glass slide surface were detected,and minimum detection concentrations of triazophos and methyl parathion were both 0.1 ppm.(3)A porous sponge-like dual-function PDMS-SERS substrate capable of simultaneous solid-phase/liquid-phase environmental pollutant sampling and detection was proposed for the first time.Considering the limitations of conventional SERS substrates in the collection of liquid phase pollutants,this study synthesized sponge-like PDMS porous materials using common white granulated sugar and cotton sugar as pore-forming agents.After hydrophilic treatment of the material and silylation treatment with APTMS,Ag NPs were loaded to prepare a sponge-like PDMS-SERS substrate,enabling dual-function sampling and detection in solid and liquid environments.By optimizing the amount of pore-forming agent(white granulated sugar/cotton sugar=1:1)and the loading layers of Ag NPs during the preparation of the substrate.It was found that under the optimal conditions,R6G was used as the probe molecule,the detection limit of the R6G was 2 femtomole.Finally,glass slide and pure water were used to simulate the solid surface and liquid environment.Triazophos and methyl parathion on the solid surface or in the liquid environment were sampled by solid surface wiping or intra-liquid adsorption and detected.The results showed that the minimum detection concentration of triazophos on the glass slide surface and in the pure water were both 0.1 ppm,and the minimum detection concentration of methyl parathion on the glass slide surface and in the pure water were 0.5 ppm.(4)The practicability(including practical application simulation,sampling efficiency,shelf life test,etc.)of the prepared flexible SERS substrate were comprehensively and systematically evaluated.First,thiram,triazophos,and methyl parathion on the surface of a variety of actual fruits were rapid detected by above-mentioned flexible PDMS-SERS substrates.The results showed that all detection limits are far beyond the national regulations maximum residue standard.Further,in the face of the current lack of testing methods and related research results on the sample collection efficiency during the SERS substrate sampling,an HPLC standard curve were established to quantitatively measure the sample collection efficiency during the sampling process of the prepared flexible SERS substrate.We found that the sampling efficiency of the SERS substrate is completely consistent with the detection sensitivity results of the actual simulation process,which also explains to some extent that the sample collection efficiency is of great significance in the actual application of the substrate.Finally,we tested the shelf life of the three SERS substrates and gave reasonable explanations for their longevity.In summary,this study provides effective solutions to several important technical difficulties faced by flexible SERS substrates in large-scale commercial applications,and lays a solid foundation for the rapid detection of actual pollutants in the field. |
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