Sensitivity Improvement of Biosensors Using Si Ring Optical Resonators

Abstract

We have been demonstrating label-free detection of a variety of antigen–antibody reactions using Si ring optical resonators. Although the detection of biomarkers for the diagnosis of diseases generally requires high sensitivity of the order of 10-9 g/ml, the detection sensitivity of our device is currently of the order of 10-6 g/ml. In this paper, we show that the sensitivity of 10-9 g/ml will be possible by adopting the following four strategies: (1) use of slot-type waveguides with light wavelength of 1.3 µm, (2) improvement of quality factor Q of the ring resonator by smoothing the surface roughness, (3) specific adsorption of the bioreceptor protein to the resonator surface, and (4) maintaining temperature within ±0.005 °C. We have also proposed the on-chip temperature compensation method without the need for temperature control of the sample. By combining the proposed approaches, the sensitivity of the biosensor will be improved by a factor of >100, thus realizing practical application of our Si ring biosensor.