Investigation of Biological Molecules at Interfaces Using Evanescent-Field Spectroscopies

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This research project is directed toward understanding the behavior of biological molecules at solid surfaces by extending and refining two techniques that are based on the interaction of the evanescent electric field of a light beam with molecules at a reflective interface. These two techniques are evanescent wave cavity ring-down spectroscopy (EW-CRDS) and surface plasmon resonance spectroscopy (SPR). An evanescent wave is formed when light undergoes total internal reflection at the interface between a higher refractive-index material and a lower refractive-index material; and its amplitude decays exponentially with distance into the lower index medium. These techniques are therefore inherently specific to interfaces and the molecules found at interfaces. EW-CRDS measures absorbance by chromophores within a few hundred nanometers of the interface, and SPR is sensitive to refractive index changes in the same region. It is proposed to refine the SPR technique by exploring a range of potential substrate materials as well, with the goal of developing more sensitive or more specific new instrumentation. This investigation will refine and introduce methods that should be widely applicable in laboratories worldwide to study the behavior of numerous biologically relevant systems. The investigation will also have a significant impact on the education of both graduate and undergraduate students. These interfacial studies will provide novel course material on cutting-edge research for Stanford's undergraduate "Theory and Practice of Quantitative Chemistry" and "Light, Pigments, and Organisms" classes that the PI teaches. The potential exists for direct undergraduate participation in these research projects as well.This award is jointly funded by the Division of Biological Infrastructure in the Directorate for Biological Sciences and by the Physics Division and the Office of Multidisciplinary Activities in the Mathematical and Physical Sciences Directorate.