Zhan Chen

We are using sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM) to investigate molecular structures of various protein molecules at different interfaces in situ. SFG is a powerful and versatile in situ nonlinear optical surface/interface probe which not only permits identification of surface/interface molecular species, but also provides information about surface/interface chemical structure. It will provide vibrational spectra of surfaces and interfaces with submonolayer sensitivity. AFM has been developed into a powerful tool to probe surface/interface structures with excellent spatial resolution through topographic, friction, or phase images. Proteins currently being studied in our group include albumin, fibrinogen, factor XII, fibrinectin, ubiquintin, and heat shock proteins. Homo-polypeptides and hetero-polypeptides are also investigated, serving as model molecules. These proteins and peptides are examined at various interfaces, including solid/protein solution interfaces, solid/water interfaces, solid/hydrophobic liquid interfaces, and solid/air interfaces. We have successfully demonstrated by SFG and AFM that a molecular level understanding of protein conformation changes at different interfaces is feasible. We hope to correlate the protein conformation changes observed by SFG and AFM to structures of native proteins, properties of different interfaces, and pH values of protein solutions. We will follow the kinetics of protein conformation changes at different interfaces.