Numerical analysis of balanced geometry selection in circular PCF SPR biosensors for cancer and bacterial detection

A gold-coated circular photonic crystal fiber surface plasmon resonance (PCF SPR) biosensor was designed for label-free, fiber-integrated detection of refractive index changes. The structure uses a silica PCF with two air hole families and a solid core. An external gold film provides the plasmonic interface so that the guided core mode couples to a surface plasmon at the gold analyte boundary. The sensing region is external, which simplifies analyte delivery and surface functionalization. Numerical analysis is performed using a finite element model. It incorporates the Sellmeier equation and the Drude Lorentz model for fused silica and gold, respectively. The models were used to obtain the refractive indices, and a comprehensive framework was used for calculating gold’s complex dielectric function. It applies a fine boundary layer mesh at the metal analyte interface. Parameter sweeps of pitch, big and small air holes, and gold thickness identify a balanced operating regime. The balanced regime provides narrow resonances and low loss, enabling wavelength and amplitude sensitivity calculations. In this configuration, the sensor differentiates six representative cancer cells, such as basal skin, Jurkat blood, MDA MB 231 and MCF 7 breast, PC 12 adrenal, and HeLa cervical. The sensor also supports water quality monitoring referenced to pure water at RI = 1.33. Among the cancer cases, the highest wavelength sensitivity is 20,714 nm/RIU, and the thinnest measured FWHM is 51 nm. The design also exhibits stable behavior under modest fabrication tolerances. It indicates practical manufacturability for compact biosensing across cellular and water contamination applications.