Au And Ag Nanoparticles:Synthesis,Assembling And Their SERS Applications

Broadly speaking,the term nanoparticle encompasses any and all types of particles(hybrid nanoparticles,core-shell nanoparticles,etc.)with a diameter on the nanoscales.Synthesis noble metal nanoparticles stand apart as the most popular group of probes.The Nobel metals have retained their preminces amongst researchers due to their stability,ease synthesis,and optical properties.Silver and gold are the most popular options,and they can provide a strong optical signal in the visible or near-IR range.During the recent work,three main challenging issues have been widely concerned for the synthesis of nanoparticles:(1)how to get nanoparticles monolayer at large area on the silicon substrate;(2)how to synthesis seed "AuNRs" with high yield;(3)how to generate silver shell on Au nanorods.To conquer this harsh issue,we have paid many efforts on this work and achieved important breakthrough and outstanding results.In chapter-3,silver nanocubes(AgNCs)were successfully assembled on silicon substrate by a two-phase method.Prepared AgNCs were firstly mixed with milli-Q water,and then cyclohexane was mixed with the solution by means of sonication.Then ethanol was added,leading to the formation of monolayer films at the cyclohexane/water interface.Finally,the monolayer film was take out from the solution and deposited on the silicon substrate.The SEM and SERS results showed that the self-assembled monolayer on silicon substrate were uniform.Taking into consideration SEM,SERS results,we found that silver nanocube monolayer at cyclohexane/water interface prepared via liquid-liquid interface at large area is uniform.Electrostatic interactions with interfacial oppositely charged molecules of hydrophilic nanoparticles assembled on substrates.These nanoparticles can easily aggregate in the mixture solution of cyclohexane and water,and can form self-assembled monolayer.In chapter-4,we have employed a symmetric silver overgrowth on the gold nanorods.For the convenience of comparison,the molar ratio of Au/Ag and quantity of seed AuNRs were same for the synthesizing of different sized core-shell nanoparticles.The absorption measurements and theoretical calculations confirm the formation core-shell nanoparticles.The thickness of shell on nanorods were tuned by varying amount of silver nitrate..LSPR of core-shell Au@Ag nanorods was tailored from visible to infrad region,which is a great evidence of uniformity and tuning of nanoparticles.Different sized core-shell nanoparticles show good stability of SERS activity by using same concentration of MBA(10-3 M)probe molecule.Au@Ag nanoparticles with the sizes of 110,130,150nm were considered as optimal SERS substrates when excitation wavelength of laser was change from 532,638,785nm respectively.This is totally supported by the three-dimensional finite-difference time-domain(3D-FDTD)calculations.Besides,this kind of well controlled different sized Au@Ag core-shell nanoparticles can be easily reproduced for the purpose of SERS measurement.