Non-invasive technologies in wearable glucose monitoring: a structured overview for the future

Diabetes management depends on regular glucose monitoring, yet conventional blood-based methods are invasive and can reduce user comfort. This review presents an overview of wearable glucose monitoring technologies, with emphasis on non-invasive approaches. It first distinguishes invasive, minimally invasive, and non-invasive monitoring and discusses the use of interstitial fluid, sweat, saliva, tears, urine, and breath as alternative sensing media. The review then summarizes optical, electrochemical, electrical/electromagnetic, and nanotechnology-enabled sensing methods, together with representative wearable and commercially reported devices. At the end, textile-based systems are compared with non-textile platforms in terms of comfort, flexibility, signal reliability, durability, and practical integration. Across these approaches, major limitations include variable relationships between alternative biofluids and blood glucose, interference from physiological and environmental factors, calibration requirements, motion artifacts, limited durability, and insufficient clinical validation. Future development requires more reliable sensing, improved wearable integration, standardized testing, and validation under real-world conditions.