Design and analysis of 2D photonic crystals biosensor based on a dual-cavity for brain tissue detection

Abstract

In this work, a new 2D photonic crystal (PhC) based biosensor is designed to be used in detecting blood molecules. The proposed structure consists of a square array of silicon (Si) rods having a refractive index of 3.5 RIU within an air background of 1 RIU. A rectangular-shaped dual-cavity, coupled to a principal waveguide, is designed. The photonic bandgap (PBG) is calculated using the plane wave expansion (PWE) method. Two wavelength ranges are covered in TE polarization. The first one is located between 864 nm and 954 nm and the second one is between 1242 nm and 1847 nm; covering the two optical windows of 1300 nm and 1550 nm. The transmission spectrum is performed based on the finite difference time domain (FDTD) method. Brain tissue detection is studied and analyzed using the proposed biosensor. The detection principle is based on detecting the changes in the refractive index of molecules. Actually, wavelength undergoes a shift in response to a change in the refractive index, within 1 up to 1.4833 RIU. The results show that the proposed biosensor exhibits a dual-sensitivity behavior with regard to both resonant wavelength and transmission intensity. The sensitivity in resonant wavelength ($S_o$) reaches a peak value of 79.03 nm/RIU with Metastasis. Furthermore, a linear positive correlation between transmission intensity and refractive index variation is achieved with a high sensitivity ($S_I$) of 285.44%/RIU. Indeed, the sensor shows a high selectivity capability in distinguishing between different brain tissues based on the shift in transmission intensity.