Inhibitory effects of a phage-derived peptide on Au nanocrystal nucleation and growth

Peptides have been shown to mediate the reduction and clustering of inorganic ions during biomineralization processes to build nanomaterials with well-defined shape, size, and composition. This precise control has been linked to specific amino acid sequence; however, there is a lack of information about the role of peptides during mineralization. Here, we investigate the nucleation and growth behavior of Au nanocrystals that are mediated by the engineered peptide AYSSGAPPMPPF. Unlike other nanocrystal synthesis schemes, this peptide produces Au nanocrystals from Au(III) ions at very low relative peptide concentrations, at ambient temperature, and in water at neutral pH. Our data show that (i) the peptide AYSSGAPPMPPF actually inhibits nucleation and growth of nanocrystals, (ii) HEPES plays an active chemical role as the reducing agent, and (iii) HAuCl4 accelerates the kinetics of nanoparticle nucleation and growth. Herein, we propose empirical rate laws for nucleation and growth of Au nanocrystals and compare kinetic rate laws for this peptide, citrate, and various other polymer ligands. We find that the peptide belongs to a unique class of nonreducing inhibitor ligands regulating the surface-reaction-limited growth of nanocrystals.