Optical sensing of biomolecules using microring resonators

TLDR

The study introduces a biosensor based on vertically coupled glass microring resonators with a Q factor of ~12,000. Balanced photodetection yields a limit of detection of 1.8 × 10⁻⁵ RIU, enabling measurement of bulk refractive index changes and avidin‑biotin binding on the ring surface. Ellipsometry and XPS confirm successful surface modification, and the sensor shows excellent repeatability with near‑complete regeneration after binding.

Abstract

A biosensor application of vertically coupled glass microring resonators with Q/spl sim/12 000 is introduced. Using balanced photodetection, very high signal to noise ratios, and thus high sensitivity to refractive index changes (limit of detection of 1.8/spl times/10/sup -5/ refractive index units), are achieved. Ellipsometry and X-ray photoelectron 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 experimentally demonstrated.