Engineering a well-ordered, functional protein-gold nanoparticle assembly

The study of interactions between proteins and nanoparticles is important to advancing applications of nanoparticles in biology, medicine, and materials science. Here, we report the encapsulation of a 5-nm diameter gold nanoparticle (AuNP) by thermophilic ferritin (tF), achieved in nearly quantitative yield under mild conditions that preserved the secondary structure, ferroxidase activity, and thermal stability of the native, 4-helix bundle protein subunits. Chromatography-based assays determined that stable protein assembly around AuNPs occurred on long time scales (similar to 48 h) and was reversible. Apparent association constants were determined at 25 degrees C for equilibrated tF-BSPP-capped AuNP samples (K-A = (2.1 +/- 0.4) x 10(78) M-11) and compared favorably to salt-assembled tF samples (K-A = (2.2 +/- 0.5) x 10(66) M-11) at the same protein concentration (0.3 mg/mL). Finally, addition of gold ions and mild reducing agent to the tF-AuNP assembly produced 8-nm diameter AuNPs with surface plasmon resonance band unchanged at 520 nm, indicative of templating by the protein shell. (C) 2013 Elsevier Inc. All rights reserved.