Mach-Zehnder type, evanescent-wave bio-sensor, in ion-exchanged glass, using periodically segmented waveguide

Integrated optical Mach-Zehnder interferometric bio-sensors have been implemented in planar glass, by using ion-exchange waveguides. To simplify the fabrication of the sensors, periodically segmented waveguide has been used as the sensing arm, thus avoiding the need to open a sensing window over this arm. To evaluate the device performance, we performed two types of measurements. First, we measured the glucose concentration in a solution. The resulting sensitivity was less than 1 g/l, corresponding to less than 10^-4 in the cover index, for a sensor with a 1 cm long sensing arm, having a segmentation duty-cycle of η = 0.5. Second, we measured the thickness sensitivity, with respect to the adsorption of avidin molecules onto the glass substrate. The resulting thickness resolution was about 1 Angstrom. Considering that the avidin concentration in the buffer solution was 2.5 μg/mL, that the full thickness of the avidin layer was 2.5 nm, and that the layer buildup time was 7 min., the corresponding sensitivity for the avidin sensor is about 0.25 nM/hr.