VIBRATIONAL-SPECTRA OF INDIVIDUAL MILLIMETER-SIZE MEMBRANE PATCHES USING MINIATURE INFRARED WAVE-GUIDES

We have used miniature planar IR waveguides, consisting of Ge strips 3 0-50 mu m thick and 2 mm wide, as evanescent-wave sensors to detect th e mid-(IR) evanescent-wave absorbance spectra of small areas of biomol ecular monolayers and multilayers. Examples include picomolar quantiti es of an integral transmembrane protein (bacteriorhodopsin) and lipid (dimyristoyl phosphatidylcholine). IR bands due to the protein and lip id components of the plasma membrane of individual 1.5-mm-diameter dev itellinized Xenopus laevis oocytes, submerged in buffer and sticking t o the waveguide surface, were also detected. A significant improvement in sensitivity was observed, as compared to previous sizes and geomet ries of evanescent-wave sensors (e.g., commercially available internal reflection elements or tapered optical fibers). These measurements su ggest the feasibility of using such miniature supported planar IR wave guides to observe structural changes in transmembrane proteins functio ning in vivo in single cells.