A Label-Free Biosensor for Protein Detection Based on Ring Slots in a Photonic Crystal

We design a miniaturized and highly-sensitive biosensor based on a photonic-crystal aslant cavity (AC) to detect protein concentrations. The AC has seven ring slots, in which input and output light is coupled through two linear quasi-waveguides. Filling the ring slots with analyte produces a shift in the resonant wavelength because of changes in the refractive index. We enhance the sensitivity by optimizing the width, position, and number of sensing ring slots. Furthermore, it can be significantly improved by infiltrating holes around the three central ring slots nearest the AC with analyte. Numerical simulations show that the final optimized device provided a sensitivity of 530.314 nm per unit refractive index with high quasilinearity and a detection limit of 1.4263 · 10−6 unit refractive index. The total footprint of the device is 86 μm2 and is ideal for ultra-compact label-free biosensing for medical diagnostics, as well as chemical and biochemical applications.