Examination Committee

Prof Cunsheng DING, CSE/HKUST (Chairperson)
Prof Andrew W O POON, ECE/HKUST (Thesis Supervisor)
Prof Jung H. SHIN, Department of Physics, Korea Advanced Institute of Science and Technology (External Examiner)
Prof Levent YOBAS, ECE/HKUST
Prof Jianan QU, ECE/HKUST
Prof Yilong HAN, PHYS/HKUST

Abstract

Optofluidics features the fusion of advanced optical and microfluidic techniques with miniaturized integration, indicating promising applications in various areas, especially lab-on-a-chip devices.  In this thesis, we focus on developing optofluidic biosensing techniques leveraging silicon photonics technology.  We proposed coupled-resonator optical waveguides (CROWs) as optical biosensors, and experimentally demonstrated a number of silicon and silicon nitride (SiN)-based CROWs integrated on optofluidic chips for various biosensing applications, including i) refractive index sensing, ii) label-free protein detection, and iii) single nanoparticle detection.

We proposed a paradigm shift in optical microcavity-based biosensing using light-scattering pattern recognition.  The sensing scheme only requires exciting CROWs at a fixed wavelength and imaging the out-of-plane elastic-light-scattering intensity patterns.  Based on correlating the light-scattering pattern at a probe wavelength with the eigenstate patterns, we devised a pattern-recognition algorithm that enables the extraction of sensing information.  We first realized the concepts for refractive index sensing.  Our experiments using silicon microring-based CROWs in the telecommunications band show a detection down to ~10-4 refractive index unit (RIU) and calibrated detection limits down to ~10-7 RIU at specific probe wavelengths.  Furthermore, we developed CROW sensors on the SiN-on-silica platform operated in the visible wavelengths.  After sensor calibration, the sensing scheme only requires a fixed-wavelength laser source and a CCD/CMOS camera, which significantly improves the practicality.

We developed SiN CROWs with surface functionalization for label-free protein detection.  Experiments for detecting streptavidin concentrations show a dynamic range of > 4 orders with the lowest detectable concentration down to ~ 1 ng/ml.  The sensing results by pattern recognition show good consistencies with the measurements using wavelength-scanning method. 

For single nanoparticle detection, we proposed detecting nanoparticle-induced perturbations by measuring the light-scattering pattern changes at CROW eigenstates.  Our experiments using SiN two-dimensional microring-based CROWs show real-time detection and counting of individual 100nm-radius polystyrene particle-binding events under fluidic flow.