Photosynthesis of Gold Nanoparticles in Presence of Proteins

This paper describes the photosynthesis of gold nanoparticles (GNPs) in the presence of bovine serum albumin (BSA). The concentration of NaAuCl₄ and the relative ratio of NaAuCl₄ to BSA are important parameters for controlling the size of the GNPs. We prepared GNPs having average diameters ranging from 7 to 50 nm by illumination (Hg–Xe lamp) of phosphate-buffered solutions (pH 3.0–11.0) containing 1 mM NaAuCl₄ and 10 μM BSA for 9 h. The size distribution of the GNPs synthesized at pH 7.0 is narrower relative to that of those prepared at other values of pH. Based on the observation that there are no GNPs formed at 25 ^°C in the absence of either BSA or illumination, we conclude that photolytic reduction is the main mechanism for the formation of the GNPs and that BSA acts as a capping agent to stabilize the as-synthesized GNPs. In addition to BSA, several other proteins, such as β-casein, conalbumin, hemoglobin, β-lactoglobulin, lysozyme, myoglobin, ovalbumin, pepsin, and trypsinogen play the same role.