AN ELECTROOSMOTIC FLOW SYSTEM WITH INTEGRATED PLANAR OPTICAL WAVE-GUIDE SENSING

A combined optical waveguide sensor and electro-osmotic how system is described. The waveguide sensor is based on the resonant mirror (RM), which uses frustrated total internal reflection to couple light into a nd out of the waveguide layer. This sensing technique can be used to m onitor refractive index, optical absorption and fluorescence within a thin surface layer. The surface of the sensor has been made compatible with electro-osmotic how. The dielectric layers used to form the wave guide sensor are deposited by chemical vapour deposition (CVD). They c onsist of a 550 nm thick layer of silica as a spacer with an 80 nm lay er of silicon nitride as the waveguide. These are deposited on a Schot t SF10 substrate, which had been etched with fluorosilicic acid to def ine the how cell. To maintain compatibility with electro-osmotic flow, a drilled glass cover plate is bonded to the waveguide to close the c hannel, leaving ports at either end to act as electrode reservoirs. El ectro-osmotic how is observed using voltages between 100 and 200 V. To detect the flow of solution, the refractive index of the solution at a point midway along the channel is monitored using the waveguide sens or. A refractive-index boundary created by adding glycerol-containing buffer to one end of the flow cell could be moved into and out of the channel by applying the appropriate polarity across the electrodes. Co ntrol experiments have been performed without a refractive-index chang e to eliminate the possibility of thermal or electro-optical effects g iving the observed signal changes.