Soft Contact-lens Biosensor for Real-time Tear Sugar Monitoring at the Eye

A soft contact-lens (SCL) biosensor for in-situ tear sugar monitoring was fabricated and tested. In contrast to the previously reported continuous glucose monitoring (CGM) devices, we focused on the relationship between blood glucose and tear glucose. The SCL biosensor was constructed by applying microelectromechanical systems (MEMS) techniques to functional polymers. The sensor has film electrodes on the surface of a rounded surface of polydimethyl siloxane (PDMS) contact-lens and glucose oxidase (GOD) was immobilized on the sensing region of the electrodes. Sufficiently adhesive and flexible electrodes were formed on the polymer device (PDMS and 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer). In the in-vitro characterization, the SCL-biosensor showed excellent relationship between the output current and glucose concentration from 0.03 to 10.0 mmol/L, which included the reported tear glucose concentrations (0.14 mM) of humans. Based on the result, in-situ tear glucose monitoring with the SCL-biosensor was carried out. The output current of the SCL-biosensor was sufficiently stable and reflected the tear glucose levels. The static glucose level in the basal tear of a rabbit was measured and estimated to 0.13 mmol/L. Since the biosensor was also possible to be sotored for more than 50 days, daily disposable application was expected with the SCL biosensor.