SPR biosensor based on etched cladding with dual-metal-layer structure for detecting AFP

We proposed a surface plasmon resonance (SPR) biosensor based on a multimode-multi-core-multimode fiber (MMF-MCF-MMF) structure, where the cladding of the MCF was etched using hydrofluoric acid (HF). The sensing region of the etched MCF was sequentially coated with Ag-GeSe-Au triple-layer films for detecting alpha-fetoprotein (AFP), a key biomarker of liver cancer cells. The structure and film thickness of the sensing region were optimized to enhance the sensitivity and detection accuracy of the fiber optic sensor. By specifically immobilizing AFP antibodies on the sensor surface, directional detection of AFP was achieved. The sensor demonstrated an AFP detection range of 0-2000 ng/mL with a sensitivity of 1.477 nm/log(ng/mL) and a low limit of detection (LoD) of 1.072 ng/mL. The proposed MCF sensor integrates optical fiber sensing with biological detection. To enhance the detection capability for low-concentration biomolecules, efforts have been focused on improving the sensor's detection accuracy and sensitivity. The biosensor enables highly specific and trace-level detection, holding significant potential for preventive screening and early diagnosis of liver cancer.