SERS Performance And Enhancement Mechanism Of Paper-Based Flexible Substrates Modified By Silver Nanomaterials

With the widespread application of surface enhanced Raman spectroscopy（SERS）in many fields,traditional SERS substrates are mostly rigid,and are far from being able to meet the requirements of arbitrary bending and folding.In addition,nanomaterials are the main factors of SERS,and their morphology,size,and bonding with the substrate can affect the Raman enhancement through the generated"hot spots".Aiming at this problem,this thesis studies the SERS effect of silver nanoparticles on flexible SERS substrates.Because Raman signal is usually weak in trace detection,it is important to study SERS with excellent performance.For conventional SERS substrates or SERS sensors,they are expensive to manufacture,non-reusable and short-lived.In this thesis,three kinds of morphologies of silver nanomaterials are loaded on three kinds of flexible substrates to form a flexible SERS substrate,and spectral analysis was performed.Silver nanospheres,silver nanowires and silver nano cubes are prepared by chemical synthesis method,polyol method and solvothermal method,respectively.Transparent paper is prepared by microfiltration method and polyvinyl alcohol matrix polishing method.Silver nanoparticles are characterized by XRD,TEM,SEM,UV-Vis,and the transparent paper is characterized by TEM,SEM,UV-Vis,thermogravimetric analyzer,nano-tensile testing system and contact angle analyzer.The silver nanomaterials with three morphologies are deposited on sulfuric acid paper,printing paper and transparent paper,respectively,to form a transparent flexible SERS substrate.Rhodamine 6G is used as a probe molecule to characterize and analyze the prepared flexible SERS substrate and its properties.A transparent flexible SERS substrate with an enhancement factor of about 2×10⁶is fabricated.After 80 times of bending and 4 times of safe folding,the substrate still has a strong SERS effect,and the relative standard deviation can reach 14.62%after 80 times of bending.In addition,the transparent flexible SERS substrate has a service life of more than 25 days,and still has a strong SERS effect after being exposed to air for 25 days,with an RSD of 11.73%.Finally,the feasibility of this substrate in practical application is demonstrated by detecting the concentration of 10^-5M Rhodamine 6G on the apple surface.Experiments show that the transparent flexible SERS substrate based on transparent paper has high sensitivity,can be reused,and has a long life.Aiming at the different effects of the prepared silver nanomaterials on the performance of transparent flexible SERS substrates,the electric field distribution of silver nanoparticles on transparent paper is studied by Finite-difference time-domain.Firstly,silver nano cubes and silver nanospheres are selected for simulation.The simulation results show that:1)The enhancement effect of a single silver nanosphere is extremely small,and as the distance between the two particles increases,the enhancement effect gradually decreases.2)The electromagnetic enhancement of a single silver nano cube is stronger than that of a single silver nanosphere.3)Due to the lightning rod effect,the prepared silver nanoparticles with sharp edges and corners can generate more hot spots than smooth spherical particles.4)When the silver nano cubes aggregates with each other,a large number of SERS active sites are formed on the coupling surface.The electromagnetic field simulation results reveal the enhancement mechanism of silver nanomaterials,which is consistent with the experimental results.