9406681 Braiman Miniature waveguide sensors will be used to detect IR absorbance changes associated with voltage-induced conformational transitions in membrane proteins. The motivation for miniaturization of the sensors is to permit in situ observation of IR spectra from membranes of intact individual cells. This, in turn, will allow IR spectroscopy to be performed as a function of cell membrane potential, which can be controlled by using a whole-cell voltage clamp. Sensitive voltage-dependent IR difference spectra should thus reveal how the living cell's membrane components responds to transient shifts in transmembrane voltage. A particular goal of this approach is to allow investigation of a variety of ion channel proteins expressed at high levels in single frog oocytes. These IR spectroscopic studies of biomembranes will depend heavily on the development of evanescent-wave sensors based on thin-film dielectric waveguides. A living cell's plasma membrane will be held in contact with a thin film of Ge deposited on ZnS or CaF2 substrate. A portion of IR light passing through the waveguide is carried in an evanescent wave that can be absorbed by molecules in the membrane. The wavelength dependence of this absorption will provide information about the vibrational modes, and thus the structures, of the lipid and protein molecules in the membrane. %%% Miniaturized biomembrane sensors based on waveguides that conduct infrared light will be developed. These waveguide sensors, consisting of thin films of infrared-transparent materials will conduct and concentrate infrared light into a small tapered region where the waveguide can be held in close contact with the membrane of a single cell, such as a 1-mm-dia. frog egg cell. Although most of the infrared light passing through the waveguide will be confined to the interior of the germanium film, a significant fraction of the light energy will be conducted in a micron-thick region outside the waveguide. This s o-called evanescent wave must therefore pass through the membrane of the cell. Selective absorption of different infrared wavelengths by the cell membrane's components will be the basis for spectroscopic analysis of their chemical structures. A particular goal is a basic understanding of how various ion- channel proteins (responsible, e.g., for neuronal signaling) change in structure in response to the varying transmembrane voltages found in living cells. However, this research should also advance our national technical capabilities in the sensitive chemical analysis of a wide variety of tiny samples, which may be of importance for such varied tasks as environmental monitoring and industrial process control. ***
