Research On Synthesis And Surface-enhanced Raman Scattering Properties Of Au-Ag Nano-assemblies

Surface-enhanced Raman scattering（SERS）,a technique that reflects information about molecular vibrations and rotations,has demonstrated great potential for applications in areas such as photo/electrocatalysis,sensing,and protein sequencing.In the early research,various kinds of noble metal nanoparticle sols of different shapes and sizes,such as gold and silver,were usually used as substrates.However,with the development of science and technology,single nanoparticle substrates have gradually failed to satisfy people’s demand.Moreover,with the appearing of plasmon hybridization effect,nanomaterials with hollow structure also come into people’s attention gradually.Meanwhile,monodisperse nanoparticles in solution are generally difficult to fabricate devices,so nano-assembly is becoming a hot research topic for researchers.A wide variety of nanoassemblies can be prepared by means of self-assembly,which has a large number of hot spots compared to monodisperse colloidal particles and can produce huge SERS enhancement.Therefore,this thesis focuses on the self-assembly of hollow gold-silver alloy nanoparticles（Au-Ag alloy HNPs）with the expectation of constructing SERS-active substrates with high sensitivity and reproducibility.The main results of this thesis are as follows:（1）Au-Ag alloy HNCs were successfully prepared by a template-free self-assembly method using Au-Ag alloy HNPs as the assembly unit through partial exchange of ligands.The obtained Au-Ag alloy HNCs with detection limits as low as 10^-8 M,exhibiting better enhancement as SERS substrates than the Au-Ag alloy HNPs and Au nanochain substrates with an intensity ratio of about 1.3:1:1.FDTD simulation results showed that the SERS enhancement of Au-Ag alloy HNCs substrates was due to the plasmon hybridization effect associated with the unique hollow structure of the alloy and the strong"hot spot"in the interstitial region of the nanochains generated by a synergistic effect between them.（2）The Au-Ag alloy HNPs were prepared by varying the size of the silver seeds to 30 nm,45 nm and70 nm,respectively,and the colloidal solution was purified by centrifugal separation to obtain Au-Ag alloy HNPs with a uniform particle size distribution and good morphology.Highly homogeneous and reproducible hollow Au-Ag alloy monolayers were prepared.The sensitivity and reproducibility of the SERS assay of the alloyed nano-monolayers assembled with three sizes of Au-Ag alloy HNPs were investigated.The results showed that the alloy membrane substrates assembled with 70 nm Au-Ag alloy HNPs had the highest detection sensitivity,demonstrating that the size of the nanoparticles directly correlated with their SERS activity,and that the activity became stronger with increasing particle size in the appropriate range（generally defined as less than 100 nm）.The highest reproducibility of results was obtained for alloy substrates assembled with 30 nm Au-Ag alloy HNPs.（3）Au-Ag alloy HNCs and nano-monolayers self-assembled with Au-Ag alloy HNPs as assembly units were used as SERS substrates for the practical detection of different concentrations of thiram acetone solutions.The detection limits of 0.05 ppm and 1 ppb for thiram were well below the EPA limits for the two substrates.Good linearity was also demonstrated（R²=0.969 and 0.997,respectively）.