Optical Slot Waveguide With Grating-Loaded Cladding of Silicon and Titanium Dioxide for Label-Free Bio-Sensing

A nanophotonic sensing platform based on slot-waveguide is proposed. We numerically investigate the effect of the structural parameters on the sensing properties. In simulation, the slot is created between the cladding made up of silicon and TiO2 grating. The presence of TiO2 overlay provides the two-fold benefit of bio-compatibility with higher sensitivity. A gold layer under top SiO2 is used to enhance optical confinement in the slot region. The surface properties of thin layers of APTMS, sol-gel prepared TiO2, and gold are experimentally analyzed. The proposed device shows full width at half maximum of 4 nm which is narrow enough to detect small changes in the refractive index of the surrounding region. The device is numerically shown to detect surface antigen HBsAg, a principal marker of hepatitis-B viral infection, with a high sensitivity of 1200 nm/RIU with a figure of merit of 300. The device offers flexibility in accommodating the bio-sample in a desirable area. An analysis on the fabrication tolerance of the device is also given.