Optimized Single-Core PCF-Based SPR Biosensor for High-Performance Early-Stage Multi-Cancer Detection

TL;DR

This work develops an SPR-based biosensor integrated with a circular-lattice PCF to enable high-sensitivity, real-time, label-free early cancer detection across skin, blood, and adrenal gland tissues. The sensor uses a thin Au plasmonic layer supported by a V2O5 adhesion layer on a silica PCF, with FEM simulations (COMSOL) guiding optimization of air-hole geometry, pitch, and metal thickness. Key performance metrics include a maximum wavelength sensitivity on the order of ~1.0×10^3 nm/RIU, resolutions in the 10^-6 RIU range, and a figure of merit exceeding 300 RIU^-1 under optimized conditions, demonstrating strong discrimination between normal and cancerous cells. The optimized design offers a practical pathway toward real-time, multi-cancer diagnostics with potential clinical impact in early-stage detection and monitoring.

Abstract

In this study, we present a highly sensitive Surface Plasmon Resonance (SPR)-based biosensor integrated with a circular-lattice Photonic Crystal Fiber (PCF) for early-stage cancer detection. The proposed sensor leverages the synergy between SPR and PCF technologies to overcome the bulkiness and limited sensitivity of traditional SPR systems. A thin gold (Au) layer, responsible for plasmon excitation, is deposited on the fiber structure, while a nanolayer of vanadium pentoxide (V2O5) is introduced to enhance adhesion between the gold and the silica background, improving structural stability and field confinement. The sensor is designed to detect refractive index (RI) variations in biological analytes, specifically targeting cancerous cells from skin, blood, and adrenal gland tissues. The optical characteristics and performance of the sensor were thoroughly analyzed using the Finite Element Method (FEM) in COMSOL Multiphysics 6.1, allowing for precise simulation and optimization. The sensor demonstrates high sensitivity within the RI range of 1.360-1.395, corresponding to the RI values of the target cancer cells. Remarkable wavelength sensitivities of 21,250 nm/RIU, 53,571 nm/RIU, and 103,571 nm/RIU were achieved for skin, blood, and adrenal gland cancers, respectively. In addition, a maximum figure of merit (FOM) of 306.424 RIU^-1 and a spectral resolution (SR) of 9.57x10^-7 RIU further affirm the sensor's exceptional detection capabilities. These findings indicate the proposed SPR-PCF sensor's strong potential for real-time, label-free biosensing applications, particularly in precise and early cancer diagnostics.

Figures (8)

• Figure 1: (a) Cross-sectional view of the proposed sensor design showing the material layers and structural components, (b) schematic layout of the glass capillary and rod assembly used in the preform fabrication
• Figure 2: Electric field distributions at the surface plasmon resonance (SPR) condition for three biological cell types using the proposed SPR-PCF biosensor. (a) Normal skin cell (RI = 1.36) at 1.925 $\mu m$; (b) Cancerous skin cell (RI = 1.38) at 2.225 $\mu m$; (c) Normal blood cell (RI = 1.376) at 2.1 $\mu m$; (d) Jurkat cell (RI = 1.39) at 2.85 $\mu m$; (e) Normal adrenal gland cell (RI = 1.381) at 2.4 $\mu m$; (f) Adrenocortical carcinoma cell (RI = 1.395) at 3.775 $\mu m$. In all cases, strong field confinement near the metal-dielectric interface and redshifts in the resonance wavelengths demonstrate effective plasmonic coupling and the sensor’s high refractive index sensitivity for reliable cancer cell detection.
• Figure 3: Confinement loss (CL) spectra of the proposed PCF-SPR biosensor for differentiating between normal and cancerous cells: (a) skin cell with refractive indices n = 1.36 (normal) and n = 1.38 (cancerous), (b) blood cell with n = 1.376 (normal) and n = 1.39 (cancerous), and (c) adrenal gland cell with n = 1.381 (normal) and n = 1.395 (cancerous). The distinct peaks in CL indicate enhanced plasmonic interaction in cancerous samples, demonstrating the sensor’s high sensitivity to biomarker-induced refractive index variations.
• Figure 4: Confinement loss variation of the proposed PCF-SPR biosensor for different air hole radii, all for adrenal gland cell detection: (a) r = 2.5 $\mu m$ and (b) r = 2.7 $\mu m$. The results highlight the influence of air hole geometry on modal confinement and plasmonic interaction strength.
• Figure 5: Confinement loss variation of the proposed PCF-SPR biosensor for different air hole radii, all for skin cell detection: (a) r = 2.5 $\mu m$ and (b) r = 2.7 $\mu m$. The results highlight the influence of air hole geometry on modal confinement and plasmonic interaction strength.