Protein-mediated autoreduction of gold salts to gold nanoparticles

Abstract

Here we report for the first time that proteins can function as unique reducing agents to produce gold nanoparticles from gold salts. We demonstrate that three different proteins, namely, bovine serum albumin (BSA), Rituximab (RIT--an anti-CD20 antibody) and Cetuximab (C225--anti-EGFR antibody), reduce gold salts to gold nanoparticles (GNP). Interestingly, among all the three proteins tested, only BSA can reduce gold salts to gold nanotriangles (GNT). BSA-induced formation of GNT can be controlled by carefully selecting the reaction condition. Heating or using excess of ascorbic acid (AA) as additional reducing agent shifts the reaction towards the formation of GNP with flower-like morphology, whereas slowing down the reaction either by cooling or by adding small amount of AA directs the synthesis towards GNT formation. GNT is formed only at pH 3; higher pHs (pH 7 and pH 10) did not produce any nanoparticles, suggesting the involvement of specific protein conformation in GNT formation. The nanomaterials formed by this method were characterized using UV-visible (UV-vis) spectroscopy and transmission electron microscopy (TEM). This is an important finding that will have uses in various nanotechnological applications, particularly in the green synthesis of novel nanomaterials based on protein structure.

Technical Note: Synthesis and Characterization of Anisotropic Gold Nanoparticles

“…The method was optimized for BSA template (8.3 µM) and gold chloride (Au 3+ ) (0.25 mM) precursor concentration in our laboratory at 25˚C over 96 hrs [15]. The reproducibility of the particle synthesis was also investigated by performing the method in triplicate.…”

“…The method described by Basu et al (2008) was optimized to produce the highest concentration of compact nanoparticles within the narrowest size distribution. In addition, the effect of alternating two different acids during pH adjustment, namely weak acetic acid and 50% HCl, on particle morphology was investigated.…”

“…The use of biotemplates has also come under the spotlight in an attempt to synthesize nanoparticles by exploiting the structural properties of various proteins/ peptides and viruses to act as scaffolding for the nucleation process [13][14][15].…”

“…Bovine serum albumin (BSA) is one such biological template which has been successfully used by Basu and colleagues (2008) in the production of anisotropic gold nanotriangles [15]. There are a number of advantages to its use in a biological, medical and biotechnological context including the fact that it is an inert, stable protein that is often used to stabilize enzymes and proteins in low concentrations (<1 mg/ml) [16]; and is known to increase the solubility of Au-NPs in aqueous solutions when coated/conjugated to the NPs [17].…”

“…In this study nanoparticles were produced according to the method of Basu et al 2008, optimized in our laboratory and were characterized by TEM, SEM, STEM-EDS, UV-Vis spectrophotometry and photoluminescence in an attempt to identify potential applications.…”