Design And Synthesis Of SERS And Colorimetric Sensors Based On Natural Cellulose Substance

With the development of modern agriculture and industry,a large number of pollutants such as pesticide residues and heavy metal ions flow into the water and soil environment,causing great damage to the ecological system.These pollutants will enter the body through the enrichment of the food chain,which are extremely harmful to human health.With the deterioration of environmental problems and the frequent occurrence of food safety issues,people are paying more and more attention to the detection of these pollutants.Nowadays,the detection technologies often rely on the expensive equipments with complicated sample preparation process,which are unrealizable to apply to the instant and on-site detection,resulting the limits of the actual application.Therefore,some sensitive and fast sensing technologies are expected to be popularized.The SERS sensors can amplify the Raman signal by several orders of magnitude,enabling the detection and monitoring of some trace organic and biological molecules,while the colorimetric sensors can quickly judge the existence and concentration of heavy metal ions by observing the change of the sensors'color via naked eyes.In addition,natural cellulose materials(filter paper)have been considered as superior candidates for the sensor substrates,due to their wide availability,low cost,portablity,non-toxicity,biodegradability,as well as the flexibility and super hydrophilicity which can benefit the collection of the analytes.In particular,the three-dimensional network structures give their large specific surface areas,leading to the more active sites and the enhancement of the detection sensitivity.In this paper,different molecules were modified on the filter paper via the silver mirror reaction or the layer by layer self-assembly method,by means of the hydroxyl and ether bonds on the surface of the cellulose fibers,thereby multifunctional paper-based sensors were obtained.The main research contents and conclusions are as follows:1.A paper-based supersensitive SERS sensor modified with Ag-nanoparticles:The SERS substrate were prepared by facile deposition of silver nanoparticles onto the cellulose fibers by means of the silver mirror reaction in a controllable manner both on the sizes of the silver nanoparticles and the silver density of the substrate.For the optimized substrate,the detection limit of R6G was as down to 10-16 M with the SERS enhancement factor of 3 × 106 calculated by finite element analysis(FEM).Moreover,the SERS sensor was successfully applied to monitor the molecular recognition in-between nucleosides of adenosine and thymidine.2.A paper-based Cu2+ colorimetric sensor modified with 1-(2-pyridylazo)-2-naphthol-6-sulfonic acid(PAN-S):A layer of TiO2 film was deposited on the surface of the cellulose paper via the surface sol-gel process,and then poly dimethyl diallyl ammonium chloride(PDDA)and PAN-S were assembled onto the cellulose paper modified TiO2 in turn by means of the effect of electrostatic adsorption to give the paper-based Cu2+ colorimetric sensor.After the recognition of Cu2+,the sensor changes from orange to purple,and the detection limit of Cu2+ in aqueous solution was 0.01 ppm observed by the naked eye.In addition,the sensor was not interfered by other metal ions,and it was suitable for the pH range of 1?9.Moreover,the sensor was also applied to the test of Cu2+ content in different tap water samples.3.A paper-based Pb2+ colorimetric sensor modified with Xylenol Orange(XO):A layer of TiO2 film was deposited on the surface of the cellulose paper via the surface sol-gel process,and then XO was self-assembled onto the cellulose paper modified with TiO2 by immersion method.Finally,a paper-based Pb2+ colorimetric sensor was obtained.After identifying Pbu+,the color of the sensor changed from orange to lavender.The naked eye detection limit for Pb2+ in aqueous solution can be as low as 10 nM.In summary,three kinds of paper-based sensors for different applications were obtained by specific modifying process of the natural cellulose materials,which can be applied to surface-enhanced Raman spectroscopy or the on-site detection of Cu2+ and Pb2+ in real water environment ttrough naked eyes.The prepared sensors have great potential for popular application,for their low price,simple operation,excellent performance and environmental friendliness.