Design of a photonic crystal biosensor using DNA filled microcavity and ring cavity coupled with waveguide

Optical biosensors can be used for effective detection and quantification of biological analyte which can be a cell, enzyme or a biomolecule. Two designs of optical biosensor are proposed in the paper using a two-dimensional photonic crystal. For both the designs, a structure possessing hexagonal symmetry with an area of 19×18 μm² is considered. Dielectric rods of Si with the refractive index of 3.47772, hole radius of 300 nm and lattice constant of 400 nm are introduced over the wafer of air. First design is based on DNA filled microcavity coupled with a waveguide. After FDTD simulation, it is observed that high quality factor of this DNA based biosensor can be utilized in the field of DNA photonics. In the second one, two ring cavities are coupled with two waveguides. Refractive index contrast is introduced by changing the refractive index of the medium surrounding both the cavities. It is observed that this change in refractive index causes a spectral shift in the transmission spectra. This property is utilized in sensing applications by considering different biomolecules with different refractive indices. In the work, both designs are allowed to operate in the visible range of 400-700 nm. This range allows these biosensors to be used efficiently in the applications such as spectroscopy, microscopy and endoscopy. Also, after calculations a high quality factor of 7108.77 is obtained which provides a precise resolution of the concerned tissue or cell.