Continuous glucose monitoring systems - Current status and future perspectives of the flagship technologies in biosensor research.

Diabetes mellitus is a chronic illness in the United States affecting nearly 120 million adults, as well as increasing in children under the age of 18. Diabetes was also the 7th leading cause of death in the United States with 270 K deaths in 2017. Diabetes is best managed by tight glycemic control, as achieving near-normal glucose levels is key to reduce the risk of microvascular complications. Currently, continuous glucose monitoring (CGM) systems have been recognized as the ideal monitoring systems for glycemic control of diabetic patients. Briefly, a CGM system measures blood glucose levels in subcutaneous tissue by attaching a CGM sensor to the skin, allowing the users to make appropriate modifications to their medical interventions according to experience or empirically derived algorithms. The principles of the glucose sensing employed in the current commercially available CGM systems are mainly electrochemical, and employ the gold standard enzyme, glucose oxidase, as the glucose sensing molecule with the combination of hydrogen peroxide monitoring or with the combination of redox mediator harboring hydrogel. Recently, by employing an abiotic synthetic receptor harboring a fluorescent probe combined with a fluorescent detection system, a chronic CGM was commercialized. In addition, the development of less or non-invasive monitoring sensors targeting glucose in tears, sweat, saliva and urine have become of great interest although their clinical relevancy is still controversial. This review article introduces current and future technological aspects of CGM systems, the flagship technology in biosensor research, which was initiated, matured and is still growing in North America.