Laser-Based Four-Core Biosensor With WS₂ Thin-Film/CeO₂-Nanorods/AuNPs Immobilization for Ascorbic Acid Detection

In this study, we present a novel optical sensing system for the real-time detection of ascorbic acid (AA), also known as vitamin C, a vital water-soluble vitamin with significant clinical relevance. AA serves not only as a biomarker for various diseases but also as a treatment for conditions such as scurvy, anemia, and cardiovascular disease. Our approach involves the development of a highly sensitive fiber optic sensor tailored for AA detection, utilizing a multimode fiber-four-core fiber (MMF-FCF) configuration. Fabrication involved advanced techniques, including fusion splicing and hydrofluoric (HF) acid etching, which created a core-mismatch structure generating sufficient evanescent waves (EWs). We immobilized tungsten disulfide (WS2) thin-film and cerium dioxide nanorods (CeO2-NRs) onto the probe's surface to enhance the sensor's performance. Thereafter, EWs excited the localized surface plasmon resonance (LSPR) phenomenon of gold nanoparticles (AuNPs) immobilized on the probe's surface, facilitating AA detection. To enhance AA sensor selectivity, the probe's surface was functionalized with the ascorbate oxidase (AOx) enzyme. The experiments utilized a laser source and an erbium-doped fiber amplifier (EDFA) to achieve precise excitation and signal amplification, enhancing the sensor's overall performance. Experimental results demonstrated a sensor sensitivity of 0.796 nm/mM and a limit of detection (LoD) of 167.71 mu M within the 0-500 mu M concentration range. These findings emphasize the sensor's potential value in clinical applications for AA detection.