High Yield Seedless Synthesis of Uniform Silver Nanoparticles with Different Sizes.

Currently, seed-mediated growth method is the dominant strategy for synthesis of silver nanoparticles (Ag NPs) with different sizes. However, it is complicated for the researchers with limited chemistry-training. In this work, monodisperse, quasi-spherical Ag NPs with different sizes were successfully produced in high yield by adding a trace amount of NaBH4 solution into the mixtures of AgNO3, ascorbic acid and cetyltrimethylammonium chloride (CTAC) as surfactants. It was found that the sizes of as-prepared Ag NPs can be tuned from 20 nm to 50 nm by adjusting the NaBH4 concentration at optimal pH (about 6.33) and CTAC concentration (0.02-0.06 M). The surface-enhanced Raman scattering (SERS) activity of 50 nm Ag NPs shows an enhanced enhancement factor for 4-aminothiophenol (4-ATP) molecules (2.5 x 10(7) for a(1) mode). Moreover, Raman signals (a(g) mode) of 4,4'-dimercaptoazobenzene (DMAB) molecules were also observed due to the laser-induced transformation of 4-ATP molecules on the surfaces of 50 nm Ag NPs during SERS measurement. Furthermore, the transformation of probe molecules on the surfaces of metal NPs during SERS measurement have to be considered.