Sarah C. Heilshorn, PhD , Stanford University
1. Project Overview:
Nanoscale materials are generating revolutionary breakthroughs in energy storage and transport materials such as high capacity lithium ion batteries and organic photovoltaic devices. These materials achieve their enhanced performance through increased ability to withstand mechanical stresses and increased interfacial surface area. However, these structures are generally sparse arrays of nanowires with a fill factor per unit volume of roughly 10-15%, which greatly limits the theoretical capacity per unit surface area of electrode. The ideal nano-architecture to maximize the theoretical capacity is unknown. Furthermore, the experimental strategies to synthesize and characterize a range of nanostructures are currently limited. By creating a flexible platform to systematically study the importance of nano-architecture on electrode capacity, we aim to elucidate the optimum nanostructure for energy storage and transport applications. Our approach utilizes the unique ability of nature to self-assemble an amazing variety of three-dimensional nanostructures from a single protein biotemplate, clathrin. We have used this self-assembling protein to create three-dimensional porous nanostructures with spherical and pyramidal geometries. These protein nanostructures are then site-specifically functionalized using non-covalent peptide-protein interactions. Through careful design of the peptide sequence, we have demonstrated scaffold functionalization to enable three different templating reactions: the synthesis of titanium dioxide, cobalt oxide, and gold nanoparticles, all at room temperature and pressure.
2. Scientific Progress:
Natural systems often utilize a single protein to perform multiple functions. Control over functional specificity is achieved through interactions with other proteins at well-defined epitope binding sites to form a variety of functional co-assemblies. Inspired by the biological use of epitope recognition to perform diverse yet specific functions, we present a Template Engineering Through Epitope Recognition (TEThER) strategy that takes advantage of non-covalent, molecular recognition to achieve functional versatility from a single protein template. Engineered TEThER peptides span the biologic-inorganic interface and serve as molecular bridges between epitope binding sites on protein templates and selected inorganic materials in a localized, specific, and versatile manner. Specifically, we functionalized identical clathrin protein cages through co-assembly with designer TEThER peptides to achieve three diverse functions: the bio-enabled synthesis of anatase titanium dioxide, cobalt oxide, and gold nanoparticles in aqueous solvents at room temperature and ambient pressure. Compared with previous demonstrations of site-specific inorganic biotemplating, the TEThER strategy relies solely on defined, non-covalent interactions without requiring any genetic or chemical modifications to the biomacromolecular template. Therefore, this general strategy represents a mix-and-match, biomimetic approach that can be broadly applied to other protein templates to achieve versatile and site-specific hetero-assemblies of nanoscale biologic-inorganic complexes.
3. Impact on PI Career:
This grant enabled my laboratory to pursue a completely new research direction in order to apply our expertise in protein-based materials to novel energy applications. This funding also enabled my laboratory to initiate several productive interdisciplinary research collaborations that were critical in facilitating our studies. Based on our scientific results, this grant provided support for me to attend the American Physical Society national conference in March 2010 as an invited speaker. In addition, an oral presentation at the American Institute of Chemical Engineers annual conference in November 2010 was supported. Partial support was provided for a manuscript currently in review as well as two peer-reviewed conference proceedings.
4. Impact on Trainees:
Stipend support of 50% was provided to one postdoctoral scholar, Todd Ostomel, Ph.D., for five months. Through this support, Dr. Ostomel was able to greatly expand his expertise in nanotemplating to include protein-based approaches. In addition, stipend support of 100% was provided to one postdoctoral scholar, Arunagirinathan Adhimoolam, for three months. Dr. Adhimoolam is an expert in cryo-transmission electron microscopy, and through this project he was able to develop new imaging protocols to characterize protein-inorganic nanoparticles. One Ph.D. graduate student, Alia Schoen, participated in the project for the duration of the support. Ms. Schoen was supported through a combination of university fellowship and grant support. Through support of ACS-PRF funds, Alia Schoen attended the AVS Conference, Materials Research Society Spring Meeting, and the American Chemical Society National Meeting to present her research results. This resulted in publication of two first-author, peer-reviewed symposium proceedings and the submission of a first-author manuscript currently in review. Additionally, Ms. Schoen was supported in a field-work assignment to the AMOLF Foundation for Fundamental Research on Matter (FOM) Laboratory at the Dutch National Science Foundation. Ms. Schoen was a visiting scientist in the laboratory of Prof. Mirjam Leunissen, where she received training on a unique methodology to quantify biomolecule self-assembly that was pioneered by Prof. Leunissen. Ms. Schoen's career goals are to pursue an academic faculty position. Finally, one undergraduate student, Ashley Seni, participated in this project for a period of three months and with additional stipend support from the Stanford Vice Provost for Undergraduate Education. Based partially on her laboratory experiences, Ms. Seni, an under-represented minority student, has elected to pursue a Masters degree in Materials Science and Engineering.