title: Silicon coupled-resonator optical-waveguide-based biosensors using light-scattering pattern recognition with pixelized mode-field-intensity distributions.
abstract: Chip-scale, optical microcavity-based biosensors typically employ an ultra-high-quality microcavity and require a precision wavelength-tunable laser for exciting the cavity resonance. For point-of-care applications, however, such a system based on measurements in the spectral domain is prone to equipment noise and not portable. An alternative microcavity-based biosensor that enables a high sensitivity in an equipment-noise-tolerant and potentially portable system is desirable. Here, we demonstrate the proof-of-concept of such a biosensor using a coupled-resonator optical-waveguide (CROW) on a silicon-on-insulator chip. The sensing scheme is based on measurements in the spatial domain, and only requires exciting the CROW at a fixed wavelength and imaging the out-of-plane elastic light-scattering intensity patterns of the CROW. Based on correlating the light-scattering intensity pattern at a probe wavelength with the light-scattering intensity patterns at the CROW eigenstates, we devise a pattern-recognition algorithm that enables the extraction of a refractive index change, Δn, applied upon the CROW upper-cladding from a calibrated set of correlation coefficients. Our experiments using an 8-microring CROW covered by NaCl solutions of different concentrations reveal a Δn of ~1.5 × 10(-4) refractive index unit (RIU) and a sensitivity of ~752 RIU(-1), with a noise-equivalent detection limit of ~6 × 10(-6) RIU.
authors.affiliation: Photonic Device Laboratory, Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
authors.forename: Jiawei
authors.initials: J
authors.lastname: Wang
authors.affiliation: Photonic Device Laboratory, Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
authors.forename: Zhanshi
authors.initials: Z
authors.lastname: Yao
authors.affiliation: Photonic Device Laboratory, Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
authors.forename: Ting
authors.initials: T
authors.lastname: Lei
authors.affiliation: Photonic Device Laboratory, Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Poon
mesh_terms: D000465:Algorithms; D015374:Biosensing Techniques / Q000295:instrumentation*; D002138:Calibration; D004867:Equipment Design / Q000295:instrumentation*; D008027:Light; D010363:Pattern Recognition, Automated / Q000379:methods; D012031:Refractometry / Q000295:instrumentation*; D012825:Silicon / Q000737:chemistry*
chemical_list: D012825:Silicon