Preparation And Surface Enhanced-raman Scattering Effect Of Three-dimensional Metal/Graphene Composite Structure

Surface-enhanced Raman scattering (SERS) has attracted increasing attentionas a powerful analytical technique in chemical and biological detections forlow-concentration molecules, DNA, pathogens, etc. In this thesis, thethree-dimensional metal/graphene composite structure as a SERS active substratewhich has high sensitivity, excellent stability and biocompatibility was fabricated.We studied its preparation process, performanceand enhancement mechanism.Three-dimensional metal/graphene structure provides a new idea for the preparationof SERS active substrate and has potential advantages in detecting tracecontaminants and biomolucules. The content in this thesis can be summarized asfollows:1. A close-packed assembly of plasmonic gold nanoparticles was fabricated ona diamond-like carbon flm by a two-step electrodeposition via reduced grapheneoxide (rGO) modulation. The size of gold nanoparticles was controlled at60nm byadjusting electrodeposition parameters. The oxygen functionalities at the rGOsurface which were controlled by changing thickness of GO provided reactive sitesfor nucleation and growth of gold nanoparticles. The Raman intensity of rhodamineB obtained from the gold nanoparticle/graphene/gold nanoparticle compositesshowed a4.3-fold increase compared with that from gold nanoparticles alone,indicating a coupling of localized electromagnetic feld enhancement and chemicalenhancement.2. Hollow gold nanoparticles (HGN) were synthesized by a sacrificial templatemethod. The hollow gold nanoparticles were assembled into monolayer by interfaeialassembly at the n-butanol/water interface and were transferred onto the ITO substrate.Combination with graphene oxide (GO) and second-time assembly of HGN, the3D HGN/GO/HGN composite structure was constructed. This composite structure had amore excellent SERS perfomance compared to the HGN alone. Furthermore, theDNA was loaded on HGN to detect SERS signal of DNA. The HGN on the ITO wasbridged with the HGN in the colloidal by the principle of complementary base pairingto generate “hot spot” and enhance the Raman signal of DNA. Compared with thegold nanoparticles, the HGN had a higher energy of surface plasmon with thedetection limit of DNA as low as0.1nM.3. A sandwich nanostructure of silver nanodendrite/graphene/gold nanoparticle(Ag/rGO/Au) was fabricated by an electrochemical method. The reduction degree ofgraphene controlled by changing the reduction time (0s,400s and800s) greatlyimpacted the nucleation and growth of gold on the top layer. The Raman signal ofRhB on Ag/rGO/Au hybrid was enhanced by9fold compared to silver dendritesalone due to efficiently transfer of excited surface plasmons and dark plasmon modeexcited by the vertically incident light in the vertically sandwich confguration. TheSERS spectrum of different levels of RhB on Ag/rGO/Au surface showed theminimum detected concentration of RhB about10nM. And the rGO protected silverfrom oxidation under ambient condition effectively. It could allow the Ag/rGO/Auhybrid to be used as an active SERS sensing substrate with high sensivity, chemicaland long-time stability.