Modern biological selection techniques such as phage display and directed evolution have identified short (10-30 amino acid) peptides with a desired function from libraries of ~1015 different sequences. Numerous reports and reviews list peptide sequences that are known to bind specifically to various surfaces (i.e. Au, Pd, GaAs, SiO2, etc.). Interestingly, many of these sequences or slight genetic variants have also demonstrated the ability to control nucleation and growth of nanometer sized inorganic crystals in solution at room temperature and neutral pH. Several studies have now been published using engineered peptides for biomineralization of different materials (Au, Ag, SiO2, Ge, Fe alloys); however, the mechanisms of nucleation and growth as a function of the peptide sequence are not understood.

In this talk, I will present results from studies on peptide-mediated growth of gold and silver nanoparticles. The kinetics of nucleation, nanocrystal growth, (and in some cases agglomeration) in a large parameter space are followed using UV-Vis absorbance in 96 well plates. Based on these screening experiments, the initial association of metal ions with peptides and subsequent nucleation and growth stages are followed with multiple angle dynamic light scattering (DLS) measurements during growth. Transmission electron microscopy (TEM) is used to image the nanocrystals and statistically relevant information on nanocrystal size, shape, and polydispersity is obtained from small angle x-ray scattering (SAXS) experiments. Finally, small angle neutron scattering (SANS) experiments are conducted with solvents contrast matched to the metal core. These contrast matched SANS experiments allow observation of solely the peptides in solution before, during, and after growth of nanocrystals. The combination of scattering techniques (DLS, SAXS, and SANS) provide unique and powerful insights into the peptide behavior leading to nucleation and growth of nanoparticles. The questions of how engineered peptides associate with metal ions, the number of peptides nucleating a particle, the number of peptides terminating the final grown particle, and how this changes during intermediate stages will be discussed in this talk. These results have broad applications in fields such as biomineralization, protein adhesion, directed assembly of nanomaterials, as well as health applications relating to metal ion processing in the human body.