PERFORMANCE OF A HIGHLY SENSITIVE OPTICAL WAVE-GUIDE MACH-ZEHNDER INTERFEROMETER IMMUNOSENSOR

We describe a highly sensitive sensor which uses the evanescent field of a reusable planar optical waveguide as the sensing element. The waveguide used is optimized to obtain a steep dependence of the propagation velocity on the refractive-index profile near the surface. The adsorption of a layer of proteins thus results in a phase change, which is measured interferometrically using a Mach-Zehnder interferometer set-up. The stability of the interferometer is such that phase changes almost-equal-to (1 x 10(-2))2pi per hour can be measured. Immunoreactions have been monitored down to concentrations of 5 x 10(11) M of a 40 kDa protein.