Integrated optofluidic label-free biosensors using a silicon-nitride-based coupled-resonator optical waveguide

In this paper, we report our recent progress in silicon-nitride-based optofluidic label-free biosensors using a surface-functionalized coupled-resonator optical waveguide (CROW) in the visible wavelengths. The working principle is based on far-field imaging of the CROW mode-field intensity distributions at a fixed probe wavelength. The imaged pattern variation reflects real-time analyte-binding information on the CROW surfaces. Our surface-functionalized 16-microring CROW reveals six eigenstates with distinctive mode-field intensity distributions. Our proof-of-concept sensing experiment at an arbitrarily chosen probe wavelength within the CROW transmission band shows a detection of streptavidin concentration down to 40 ng/ml.