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

ABSTRACT 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.