Integrated optics ring-resonator sensors for protein detection

Using an integrated optics ring-resonator biosensor, we have demonstrated the detection of protein in low concentrations. We detected 0.3 nM of avidin in a buffered saline solution; the calculated detection limit is 0.1 nM (6.8 ng/ml) for avidin, which compares favorably with those of other optical protein detection techniques. Further improvement is possible. Our ring resonator utilizes SixNy/SiO2 waveguides, which, owing to evanescent field interaction, change the effective refractive index when target molecules are immobilized on their surfaces. The selectivity of the sensor depends on the biotin surface coating, which causes the specific binding and immobilization of avidin. (c) 2005 Optical Society of America.