Integrated optical waveguide attenuated total reflection spectrometry and resonance Raman spectroscopy of adsorbed cytochrome c

Abstract

The heme group of cytochrome c (Cyt C) has resonance absorptions at 520 and 550 nm that arise from x-y degenerate in-plane electronic transitions of the heme moiety. In the present paper, horse heart Cyt C was adsorbed to the surface of a micron-thick silicon oxynitride integrated optical waveguide configurated into a liquid flow cell and prism-coupled with 514.5-nm laser light that was polarized horizontal (TE) and nearly vertical (TM) with respect to the waveguide surface. The adsorbed protein film absorbed light from the evanescent field at the waveguide surface, resulting in two measurable quantities: (1) an increased attenuation of the guided mode intensity in the waveguide and (2) excitation of Cyt C resonance Raman emission