Protein-protected nanoparticles from rapid expansion of supercritical solution into aqueous solution

Nanocrystalline silver particles were prepared via a supercritical fluid processing technique RESOLV (Rapid Expansion of a Supercrifical Solution into a Liquid SOLVent) coupled with chemical reduction. The preparation involved the rapid expansion of a supercritical ammonia solution of silver nitrate into an ambient solution that contained sodium borohydride or hydrazine as reducing agent and poly(N-vinyl-2-pyrrolidone) (PVP) or bovine serum albumin (BSA) protein as the protection agent for the resulting nanoparticle suspension. The nanoparticles were characterized using UV/vis absorption, X-ray powder diffraction, and transmission electron microscopy methods. The results show that the BSA protein-protected Ag nanoparticles are much larger than those obtained with PVP as protection agent under otherwise the same experimental conditions but still maintain relatively narrow size distributions. Mechanistic implications of the results are discussed.