A comprehensive review of non-invasive optical and microwave biosensors for glucose monitoring

Frequent glucose monitoring is essential for effective diabetes management. Currently, glucose monitoring is done using invasive methods such as finger-pricking and subcutaneous sensing. However, these methods can cause discomfort, heighten the risk of infection, and some sensing devices need frequent calibration. Non-invasive glucose monitoring technologies have attracted significant attention due to their potential to overcome the limitations of their invasive counterparts by offering painless and convenient alternatives. This review focuses on two prominent approaches to non-invasive glucose sensing: optical- and microwave-based methods. On one hand, optical techniques, including Raman and near-infrared (NIR) spectroscopy, leverage the unique spectral properties of glucose molecules to measure their concentration in tissues and biofluids. On the other hand, microwave sensing leverages the dielectric properties of glucose to detect concentration changes based on impedance measurements. Despite their promise, optical- and microwave-based technologies face challenges such as signal interference and high variability due to tissue heterogeneity, which impact their accuracy and reliability. This review provides a comprehensive overview of the advancements of these non-invasive methods, highlighting their technical implementation, limitations, and their future potential in revolutionizing glucose monitoring for diabetes care.