PhD Chemistry, Colorado State University, 1995
NSF Postdoctoral Fellow, Pennsylvania State University, 1995-1997
David and Lucile Packard Foundation Award, 2000
National Science Foundation Career Award, 2000
Arnold and Mabel Beckman Foundation Young Investigator Award, 1999
Society of Electroanalytical Chemistry Young Investigator Award, 1999
National Science Foundation Post-doctoral Fellowship, 1995
Procter and Gamble Research Fellowship, Colorado State University, 1993
Biomolecule-Mediated Materials Synthesis, Nanoparticle Therapeutics, Protein/Protein Interactions
The Feldheim group is working at the interface between cell biology and materials chemistry. One of our project areas involves the synthesis and use of nanoscale materials as tools for visualizing, discovering, probing and disrupting biomolecule interactions in cells. Part of our effort in this area is focused on studying polyvalent binding interactions between drug-coated metal nanoparticles and cell surface receptors. We are addressing fundamental biophysical questions such as: How do nanoparticle size and the number of drugs per particle influence nanoparticle/receptor binding interactions? Can the length and rigidity of the linker connecting the drug molecule to the nanoparticle be used to tune binding thermodynamics? We are asking similar questions regarding the binding interactions of axon guidance protein ligands and their receptors on developing nerve cells. By attaching axon guidance proteins to metal nanoparticles in well-defined ways we hope to better understand how spatial relationships between proteins govern their function.
In a second research thrust area we are exploiting the propensity of biomolecules to evolve in response to selection pressures for the synthesis of novel materials.In these projects large libraries (e.g., 1012 unique sequences) of peptides, RNA, or DNA are synthesized and exposed to metal and/or organometallic precursors (e.g., HAuCl4, Co2+, Fe2+). The hypothesis is that some sequences will be able to assemble the precursors into solid materials. However, because each sequence in the initial mixture differs in primary sequence and 3D structure, many different inorganic crystal types and compositions are possible. In fact, one expects that many of the initial sequences are incapable of nucleating a crystal; others may grow crystals differing in size, shape, or physical property. A separation is then performed to isolate the desired material. For example, in “selection cycle 1” sequences not bound to a crystal are easily removed by centrifugation. These sequences are said to be “selected” out; that is, only those sequences that grow crystals survive and are carried forward to the second cycle. Sequences that are carried forward may constitute a minor fraction of the overall sample. However, they can be amplified and used in the next cycle. In subsequent cycles, more stringent selection pressures may be imposed. It may be possible to select for sequences that grow crystals possessing a certain catalytic, electronic, photophysical, magnetic, etc. property. After several cycles (typically around 10), the initial biomolecule library of sequences is narrowed to a much smaller pool (hundreds) containing families of sequences that grow crystals with the desired property. This work is helping us formulate a deeper fundamental understanding of the mechanisms by which organisms in the biosphere synthesize such an extraordinary range of solid-state materials. These methods are also being applied to the discovery of new materials for applications ranging from disease diagnosis and treatment to nanoscale electronics and alternative energy.