Nanocvity-coupled photonic crystal waveguide as a biosensing platform

Abstract

A multi-dimensional artificially designed periodic dielectric media known as Photonic Crystal (PC) brings the opportunity of a revolution in communications and sensing much closer because of the special property of PC such as the potential of boost field-matter interaction. As a result, PC sensors present the probability of multi-analyte and highly compact sensing methods as well as the capability of the detecting a small quantity of analyte (Nano-liters) and low-concentrated samples (Pico-moles), which may be beneficial approach over conventional approaches like fiber optic and slab waveguide sensors. In this dissertation, a Bio-sensing platform based on nanocavity-coupled photonic crystal waveguide (PCW) is proposed for diseased cell detection. Proposed label-free waveguide-cavity coupled nanostructure with high-Q is designed and analyzed to exhibit high sensitivity and high selectivity against five different cancer cells. The research work is performed using a thin two dimensional PC slab having dielectric in air configuration where silicon rods are arranged in hexagonal array. A PCW is induced by missing a row of dielectric rods which gives a wide Photonic Band Gap (PBG) in transmission spectra. The introduction of a nanocavity in the PCW leads to a sharp resonance which makes it useful for detection of infected cells. A pair of dielectric holes on each side of cavity is acting as reflector. Presented nanocavity-coupled waveguide structure is optimized by shifting and by changing the radii of adjacent rods around cavity. Sensing principle is observed change in the refractive index (RI) due to presence of analyte. It is observed through 2-D Finite Difference Time Domain (FDTD) method in the transmission spectra that the resonant wavelength of biosensor is red shifted on increasing the RI of the cavity imposed by the presence of cancer cell in blood sample. The change observed in RI is positive because of presence of more content of protein in cancer cell as compared to normal cell. The reported sensitivity and quality factor of the proposed platform are acceptable for cell-level detection of various diseases. The proposed design also shows sufficiently separated resonant peaks for different cancer cells which offer us a possibility of highly selective label-free cancer detection.