pubs.acs.org/Langmuir This article not subject to U.S. Copyright. Published 2009 by the American Chemical Society
Inhibitory Effects of a Phage-Derived Peptide on Au Nanocrystal Nucleation and Growth Scott K. Stanley,*,† Matthew L. Becker,*,‡ Eric K. Lin, and Wen-li Wu National Institute of Standards and Technology, Polymers Division 100 Bureau Drive, Gaithersburg, Maryland 20899. †Current Address: P&G, Beckett Ridge Technical Center, 8611 Beckett Road, West Chester, OH 45069. ‡Current Address: Department of Polymer Science, University of Akron, Akron, OH 44325-3909. Received April 6, 2009. Revised Manuscript Received July 6, 2009 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.
Introduction Many organisms have the ability to carry out biomineralization processes where they sequester ions from their environment and convert them into hierarchically structured materials. These processes are often multistep and multiscale in nature, utilizing proteins and shorter peptides to mediate the reduction of ions, form clusters, and regulate the nucleation and growth of nanomaterials. Biomineralization peptides and proteins have naturally evolved allowing organisms to build structural elements (shell, bone, and tooth) as well as more advanced natural biodevices (waveguides, lenses in eyes) from the most abundant elements.1,2 Now it is possible to expedite evolutionary processes in the laboratory to identify new peptides that build non-natural materials. Biological selection techniques (phage display, cell surface display, yeast display, etc.) have recently been applied to material targets yielding “engineered peptides” that bind strongly and specifically to a range of different metal, semiconductor, oxide, and biomineral surfaces.3,4 These engineered peptide sequences not only interact with existing surfaces but also can exert precise control over composition, shape, and size of inorganic nanocrystals mineralized from the atom up. This synthesis occurs at room temperature, in water at neutral pH, and seemingly with no added reducing agent. A number of questions exist about these processes, centered on the mechanism of how peptides build nanomaterials from the atom up. If these remarkable processes are better understood, peptides may be designed for numerous applications including advanced materials, health (for pathological mineralization), and biocatalysis. *To whom correspondence should be addressed. E-mail addresses:
[email protected];
[email protected]. Fax: 301-975-3928. Tel: 301-975-6219. (1) Mann, S. Biomineralization; Oxford University Press: Oxford, U.K., 2002. (2) Kaim, W.; Schwederski, B. Bioinorganic Chemistry: Inorganic Elements in the Chemistry of Life; John Wiley & Sons: West Sussex, 1996. (3) Sarikaya, M.; Tamerler, C.; Jen, A. K. Y.; Schulten, K.; Baneyx, F. Nat. Mater. 2003, 2, 577–585. (4) Roy, M. D.; Stanley, S. K.; Amis, E. J.; Becker, M. L. Adv. Mater. 2008, 20, 1830–1836.
10886 DOI: 10.1021/la901222k
In this paper, we investigate the biomineralization of Au nanocrystals mediated by the engineered peptide AYSSGAPPMPPF. This peptide was identified by Naik et al. through phage display for strong metal binding5 and subsequently demonstrated as a peptide that builds small (
