My lab works at the intersection of modern research directions in the physical and biological sciences. On the physical side, the past two decades have seen a strong emphasis on nanometer-scale science and technology, both in the development of new tools to explore nanometer-scale systems and in the novel physical properties that emerge at that scale. On the biological side, there has been a drive toward more quantitative research, including a growing sense that life's complex molecular constituents must be studied as interacting systems rather than in isolation. These trends represent significant challenges and have encouraged interdisciplinary work in the physical and biological sciences.
I have directed my lab's research towards scientific questions and technical challenges at this physical/biological interface. I have focused specifically on two areas: Membrane Electrostatics and Biological Nanophotonics.
Membrane Electrostatics: The biological membrane is the least understood and arguably the most important cellular component since it forms the boundary between the cell and its environment, as well as the boundary for the cell's organelles. These membranes consist of a 2-D sheet of thousands of different types of amphiphilic molecules which are highly mobile in the membrane plane. Since the extreme complexity of natural biological membranes often precludes a fundamental understanding of their physical properties, researchers turn to synthetic phospholipid bilayers as membrane models. These lipid membranes create a complex electrostatic environment due to their high density of charged and dipolar chemical groups and their large variation in dielectric constant between the aqueous and hydrophobic phases. Since electrostatic effects are ubiquitous in biomolecular interactions, it is imperative to understand the membrane's electrostatic environment and how it depends on lipid composition.Â We have applied the atomic force microscope (AFM) to this research area. We have mapped the surface potential of heterogeneous membranes at nanometer-scale resolution, and measured the dipole potential of lipid membranes.
Biological Nanophotonics: Gold and silver nanoparticles exhibit strong spectral scattering and absorption peaks at visible wavelengths due to a resonant excitation of their free electrons referred to as a localized surface plasmon resonance (LSPR). While the theoretical basis for this effect was described 100 years ago, research in the field has exploded over the past decade due to new chemical and lithographic methods to produce nanoparticles with controlled shape and tunable plasmon resonances. Our work on biological and biomedical applications of LSPR requires an interdisciplinary approach which includes studies of nanoparticle optical properties (physics), synthesis and surface modification (chemistry), and interactions with biological systems (molecular biology). Our goal is to make fundamental advances in these areas to support the powerful diagnostic and therapeutic biomedical applications of LSPR nanoparticles. In addition, we are developing LSPR-based immunoassays that are needed to measure simultaneous expression levels of many proteins to unravel complex biological networks.