Biosensor system for continuous glucose monitoring in fish

A biosensor system was developed for continuous estimation of blood glucose in fish. Because it is difficult to measure blood components in real-time due to decreased sensor output resulting from blood coagulation and coalescing blood proteins at the sensor placement site, we used the eyeball scleral interstitial fluid (EISF) as the site of sensor implantation. Evaluation of the relationship between EISF and blood glucose concentrations revealed that the blood glucose concentration correlated closely with the EISF glucose concentration (y = 2.2996 + 0.9438x, R = 0.960, n = 112). To take advantage of the close correlation between blood and EISF glucose, we prepared a needle-type enzyme sensor for implantation in the fish sclera using a flexible wire electrode. The sensor provided a rapid response, good linearity, and reproducibility. Continuous glucose monitoring could be carried out by implanting this needle-type glucose sensor onto the eye. The findings indicated that the glucose concentration increased with sensor output current over time, and that changes in the blood glucose were continuously reflected in the EISF. The glucose concentration was estimated based on the one-point or two-point calibration methods. The two-point calibration method yielded the most accurate glucose monitoring (blood glucose range of 70–420 mg dL−1) over 160 min. Sensor-estimated glucose and whole blood glucose values were highly correlated (y = 0.4401 + 0.8656x, R = 0.958).