Tunable Microstructured Silicon Waveguide Based Fabry-Perot Interferometric (Si-FPI) Label-Free Bio-Sensor for Cancer Detection

The compatibility of both silicon on insulator (SOI) and phase-changing materials such as vanadium dioxide (VO₂) to the CMOS-based fabrication process gave birth to a new breed of sensing devices. These optical sensors are robust, small in size, and require less power and volume of precious analyte for analysis. In this paper, we propose and design a 2D linear Fabry-Perot(FP) label-free bio-sensor for different types of cancer cell detection. A silicon strip waveguide supported on silica with longitudinal ends terminated by the conductive VO₂ behaves like a linear optical resonator. Sensing occurs when the evanescent tail of the guided mode interacts with the changing external refractive indices of different analytes leading to a shift in resonant frequency. The proposed model was simulated and analysed using the finite element method provided in COMSOL Multiphysics. Analysis performed for the 4 μm long resonator having 1.28 μm thick VO₂ coating showed the maximum sensitivity of about 12.292 THz/RIU (101.44nm/RIU) for the cervical cancer. The overall sensitivity response of the investigated optical sensor is 12.312 THz/RIU (101.16 nm/RIU) with a correlation coefficient (R²) equal to 0.999. The detectable change in full width at half maximum (FWHM) of resonating mode from 3.6552 to 3.6960 THz for varying external refractive index (RI) makes the sensor immune to laser frequency fluctuations, a common source of noise in most of the resonant frequency shift-based sensing devices. The reported sensing structure has potential applications for highly sensitive label-free optical bio-sensing.