Optical Sensing of Biomolecules Using Microring Resonators

Abstract—A biosensor application of vertically coupled glass mi-croring resonators with Q ∼ 12000 is introduced. Using balanced photodetection, very high signal to noise ratios, and thus high sensi-tivity to refractive index changes (limit of detection of 1.8 × 10−5 refractive index units), are achieved. Ellipsometry and X-ray pho-toelectron spectroscopy results indicate successful modification of biosensor surfaces. Experimental data obtained separately for a bulk change of refractive index of the medium and for avidin-biotin binding on the ring surface are reported. Excellent repeatability and close-to-complete surface regeneration after binding are ex-perimentally demonstrated. Index Terms—Biomedical transducer, cavity resonator, circular waveguide. I