Studies On Solution Preparation And Properties Of Gold-silver Alloy SERS Substrates

Raman spectroscopy is a fingerprint spectrum of molecules,which contains unique structural information of molecules.It can be used to identify the type of substances,determine the concentration of substances,and understand the crystal structure.It has obvious advantages over other vibration spectra.Surface enhanced Raman scattering(SERS)spectroscopy can enhance the intensity of Raman spectroscopy by 10 orders of magnitude,and has potential applications in the fields of environmental monitoring,biomedicine,food safety,drug control,and trace analysis.In recent years,with the development of portable Raman spectrometers,SERS technology has been able to be applied to real-time and rapid on-site detection.Therefore,finding new SERS active materials and obtaining high-performance SERS substrates at low cost have become an important research topic.So far,two common materials used in SERS substrate are Au and Ag.The SERS substrate prepared by Au has high stability but poor SERS sensitivity;the SERS substrate prepared by Ag has high sensitivity but poor chemical stability.Since the gold-silver alloy material combines the advantages of the two metals,it overcomes the shortcomings of the two,and is expected to become a new SERS material.In this thesis,gold-silver alloy SERS substrates were successfully prepared by a solution processed method,and their performances were systematically characterized.The following research results were obtained:(1)By improving the Brust method,we prepared alloy nanoparticles with controllable Au and Ag mole fractions.Using these alloy nanoparticles,we assembled alloy SERS substrates composed of randomly distributed nanoparticles with their diameters range from 10 to 100 nm.There are large quantities of SERS enhancement"hot spots"buried in the substrates.(2)The characterization of SERS substrates with different gold and silver mole ratios shown that the sensitivity of SERS substrates increases significantly with the increase of Ag content.The alloy SERS substrate combined the advantages of gold and silver,showing both good stability and excellent SERS performance.The Au₁Ag₈alloy substrate can homogeneously detect R6G of 10^-12 M,which is close to the detection level of single molecule,and its enhancement factor reaches 5.1×10⁸.(3)The finite-difference time-domain(FDTD)method was used to theoretically study the intensity of localized electromagnetic field between the gold-silver alloy nanoparticles,and the relationships between the local SERS enhancement factors and the composition of the alloy nanoparticles.The theoretical results are consistent with the experimental results,further confirming the enhancement mechanism of the alloy SERS substrate.