Unusual reactivity of a silver mineralizing peptide

Abstract

The ability of peptides selected via phage display to mediate the formation of inorganic nanoparticles is now well established. The atomic-level interactions between the selected peptides and the metal ion precursors are in most instances, however, largely obscure. We identified a new peptide sequence that is capable of mediating the formation of Ag nanoparticles. Surprisingly, nanoparticle formation requires the presence of peptide, HEPES buffer, and light; the absence of any one of these compromises nanoparticle formation. Electrochemical experiments revealed that the peptide binds Ag+ in a 3 Ag+:1 peptide ratio and significantly alters the Ag+ reduction potential. Alanine replacement studies yielded insight into the sequence-function relationships of Ag nanoparticle formation, including the Ag+ coordination sites and the residues necessary for Ag synthesis. In addition, the peptide was found to function when immobilized onto surfaces, and the specific immobilizing concentration could be adjusted to yield either spherical Ag nanoparticles or high aspect ratio nanowires. These studies further illustrate the range of interesting new solid-state chemistries possible using biomolecules.

Figure 1

UV-visible spectrum and TEM image of Ag particles formed in a solution containing 690 µM Ge8, 10 mM AgNO₃ and 100 mM HEPES, exposed to ambient light and room temperature for 24 hrs.

Figure 2

Cyclic voltammograms of solutions containing 690 µM Ge8, 100 mM HEPES and A) 1, 2 and 3 molar equivalents of AgNO₃:Ge8 and B) 4 molar equivalents of AgNO₃. Working, auxiliary, and counter electrodes were glassy carbon, Pt, and Ag/AgCl, respectively.

Figure 3

TEM image of particles formed using Ge8 containing alanine instead of histidine.

Figure 4

A) and B) TEM images of curled wires formed via immobilized Ge8 incubated in 10 mM AgNO₃ and 100 mM HEPES. C) Diffraction pattern of curled wires with d spacings corresponding to 1 (111), 2 (220), 3 (420) labeled.

Figure 5

Summary of the peptides examined in this study and their ability to mediate the formation of Ag nanoparticles.