Synthesis and Properties of Au Nanoparticles with Various Sizes

Properties of Au nanoparticles (NPs) caused by various sizes (5-12 nm) were studied in this article. Au NPs capped with citrate of various sizes were synthesized by two methods including trisodium citrate dihydrate reduction of chloroauric acid tetrahydrate and sodium borohydride reducion of chloroauric acid tetrahydrate. Au NPs were characterized and measured by using transmission electron microscope (TEM), UV-vis-NIR absorption spectroscopy, and surface Raman scattering. The results of experiment indicated that the size of Au NPs was related to the type of reducing agent and molar ratio of reducing agent and chloroauric acid. The weaker the reducing capacity of the reducing agent or the lower the molar ratio, the bigger the size of Au NPs is. The max wavelength of absorption peak for the citrate-capped Au NPs is red-shifted with the increase of particle diameter. Raman scattering observed from Au NPs of various sizes is found to be NP size-dependent. It is clear that the bigger Au NPs are more apparent in the Raman scattering determination. Size-tunable Au NPs should be crucial for biosensors, particularly as Raman-tag particles.