Towards aqueous gold nanoparticles with buffer resistance and high concentration.

High-concentration gold nanoparticles stabilized by poly(vinylpyrrolindone) (PVP) are prepared through modified citrate-reduction method. The modified approach possesses all the advantages of the popular citrate reduction method. With PVP as weak ligands as well as spatial effects for the metal nanoparticles, the control of the size and size distribution of the gold nanoparticles in the size range between 10 and 30 nm was achieved via maintaining balanced nucleation and growth by tuning the feed ratios of the metal precursors and reducing reagents. As a modified procedure to gold nanoparticles, PVP-stabilized gold nanoparticles are more stable in a broad range of pH and different buffers than conventional gold colloids. Because only PVP are employed in the new synthetic schemes, surface modification and functionalization of the resulting gold nanoparticles through small molecular ligands can be readily carried out.