Vitamin D Biosensors: Current Status in Optical and Electrochemical Point-of-Care Applications.

Vitamin D plays a critical role in human health, and its deficiency has been associated with dysfunction across multiple physiological systems, contributing to a wide range of medical conditions, including cancer, infertility, and immune-related disorders. Accurate and prompt quantification of vitamin D levels is therefore essential, as it enables personalized supplementation strategies that may lead to meaningful improvements in patients' lives. In this review, the emerging role of point-of-care (POC) technologies in vitamin D assessment is examined by focusing on three main aspects: (i) how POC platforms expand the analytical capabilities available to clinicians and researchers by providing faster, lower-cost, and more patient-centered alternatives to conventional laboratory-based assays; (ii) how early and decentralized monitoring of vitamin D levels may support improved prevention and management of vitamin D-related conditions; and (iii) a critical overview of current optical and electrochemical biosensing strategies for vitamin D detection and quantification. Finally, both proof-of-concept biosensors and commercially available devices are discussed, with emphasis on their technological readiness, physiological relevance, and compliance with the RE-ASSURED criteria.