LAUSR

Silicon microring resonators are widely used as optical biosensors because of their high sensitivity and promise of low-cost mass-manufacturing. Typically, they only measure the adsorbed molecular mass via the refractive index change they detect. Here, we propose and demonstrate a silicon microring biosensor that can measure molecular thickness and density as well as electrochemical activity simultaneously, thereby enabling quantification of the conformation of surface-immobilized biological and molecular layers in real time. Insight into the molecular conformation is obtained by recording the resonance shift from two geometrically distinct ring-resonators connected to a single access waveguide. The resonant cavities both support a single TE polarized optical mode but have different widths (480 and 580 nm); the extent of their evanescent fields is thus very different, providing different depth-resolution of the interaction with a molecular layer on the sensor surface. By combining the optical shift from t...