High-Sensitivity SPR Biosensor for Tumor Cell Exosome Detection Based on Ge-Doped Fiber Core PCF

Current exosome detection technologies are constrained by limited sensitivity and refractive index (RI) detection ranges. To address this, this study proposes a biosensor based on germanium-doped photonic crystal fiber (PCF) and surface plasmon resonance (SPR) technology. Featuring a D-shaped structure with three layers of periodic pores, a germanium-doped core, and a gold film coating, this sensor extends the effective RI detection range to 1.00-1.45 RIU and achieves a peak wavelength sensitivity of 30 000 nm/RIU at 1500 nm. Simulation and optimization results demonstrate that this sensor can distinguish normal exosomes (1.35-1.38 RIU), tumor-derived exosomes (1.39-1.42 RIU), and pro-metastatic exosomes (1.43-1.45 RIU). Sensitivity significantly increases in the high-RI range (> 1.42 RIU), with corresponding maximum detection accuracies of 5 × 10^-5, 1.6 × 10^-5, and 3.33 × 10^-6 RIU, respectively. This sensor provides a label-free, high-performance detection tool for early postoperative micrometastasis surveillance, thereby enhancing cancer management efficacy.