Metasurface-based lab-on-fiber biosensor for label-free detection of vitamin D

The growing need for effective vitamin D assessment has emphasized the importance of developing rapid, accurate, and user-friendly detection tools, particularly for integration into Point-of-Care (PoC) diagnostic devices. Detecting 25- hydroxyvitamin D3 (25(OH)D3), the main circulating form of vitamin D, poses significant challenges due to the intricate sample preparation and its small molecular size, which necessitates highly sensitive detection technologies. Recent studies have explored alternative methods to traditional approaches; however, these methods still have several limitations, such as space requirements, limited sensitivity, expensive protocols, and reliance on external conditions. This work introduces an innovative, label-free Lab-on-Fiber (LoF) biosensing platform tailored for the precise detection of 25(OH)D3. The sensor device integrates plasmonic metasurfaces onto the tip of a single-mode optical fiber, offering high sensitivity combined with a compact design. A carefully crafted pipeline was implemented to optimize biofunctionalization protocols ensuring high affinity and specificity. The metasurface-enhanced LoF biosensor demonstrated excellent performance, enabling detection of 25(OH)D3 across clinically significant ranges (4-160 ng/mL) in both buffer solutions and complex biological matrices. Notably, the platform achieved a limit of detection (LOD) of 1.40 ng/mL in saline buffer and 0.85 ng/mL in complex matrices. These findings confirm the platform's capability to accurately detect small molecules in a label-free configuration, with sensitivity and specificity comparable to conventional clinical methods. Its compact structure and high sensitivity make it a promising tool for the development of cost-effective, quick, and easy-to-use PoC diagnostic devices.