Development of a biocompatible glucose biosensor for wireless and real time blood glucose monitoring of fish

Abstract

We developed glucose biosensors coated with biocompatible polymers to rapidly monitor glucose levels in free-swimming fish. Biocompatible polymers have a similar structure to living organisms and are thus used to make metallic materials more compatible with the living body. We focused on three widely used biocompatible polymers, 2-methacryloyloxyethyl phosphorlycholine (MPC) polymers, polypyrroles, and polyurethanes, to achieve biocompatibility of our glucose biosensor. The developed glucose biosensor has a Pt-Ir wire (φ0.178 mm) as the working electrode and Ag/AgCl paste as the reference electrode. The biosensor was first coated with Nafion to prevent coexisting substances such as ascorbic acid and uric acid from interfering with the sensor output current, and then glucose oxidase (GOx) was fixed on top of the Nafion layer along with biocompatible polymers. The sensor was inserted into the fish eyeball interstitial scleral fluid (EISF), which contains low levels of proteins and correlates well with the glucose levels in the whole blood. Those three sensors were tested for durability and sensors coated with MPC polymers (Nafion/GOx/MPC sensor) proved to be most durable: the sensor output current maintained 93% output for 15 h in standard glucose solution, and 80% in EISF for 8 h, whereas the output current of the other sensors decreased more rapidly overtime. We then inserted Nafion/GOx/MPC sensor to wirelessly monitor EISF glucose levels in free-swimming fish. One-point calibration method was used to calibrate the sensor output current. As a result, 24 h of wireless monitoring was successfully achieved.