Toward continuous and non-invasive monitoring: a scoping review of in vitro blood glucose devices from electrochemistry to optics and micro-system integration

MARD of nearly 1.31% to wearables with about 99% of points in clinically acceptable error-grid zones. Additionally, from a system perspective, it highlights microfluidics, MEMS, flexible electronics, and nanomaterials for wearable integration and antifouling. Finally, it identifies accuracy limits for tissue optics or dielectric effects, individual variability, calibration, lag, drift, and lifetime, and calls for scenario-based stress testing and multi-center validation.