Design and Bulk Sensitivity Analysis of a Silicon Nitride Photonic Biosensor for Cancer Cell Detection

Abstract

Bulk sensitivity is an important parameter to validate the efficiency of the photonic waveguide sensor. Due to recent advancements in point-of-care silicon photonic biosensing, the focus is to identify the effective way to improve sensitivity. Integrating polydimethylsiloxane (PDMS) microfluidic channel in sensor architecture decreases the sensitivity due to leakage of molecules at edges. The silicon nitride (SiN4) Mach–Zehnder interferometer utilizes the refractive index of different cancer cells (1.39–1.401) to determine the bulk sensitivity. The proposed gradient step rib-slot structure of 970 nm wide and 400 nm thickness is designed to hold the liquid sample without any PDMS material. This novel waveguide exhibits high waveguide bulk sensitivity $S_{w,\text{bulk}}$ and device bulk sensitivity $S_d$ compared with the gradient rib waveguide. We achieved a waveguide bulk sensitivity $\left(S_{w,\text{bulk}}\right)$ of 2.0699 RIU/RIU and device sensitivity $\left(S_d\right)$ of 568 nm/RIU through finite-difference time-domain (FDTD) analysis.