Fluorescence interference-contrast microscopy of cell adhesion on oxidized silicon

Standing modes of light in front of the reflecting surface of silicon modulate the excitation and emission of fluorescent dyes. This effect was used to determine the distance of a biomembrane from an oxidized silicon chip. The membrane of a red blood cell (ghost) was stained with a cyanine dye and attached with poly-lysine to a surface structured with microscopic steps of silicon dioxide on silicon. The system was illuminated in a microscope. The fluorescence intensity of the membrane depended on the height of the steps. The data were fitted by an optical theory which accounts both for the interference of the exciting light and for the interference of the emitted light at a finite aperture. The distance between the membrane and the silicon dioxide was determined to be 12 nm.