Development of Self-Powered Glucose Biosensors for Fish Stress Monitoring

Abstract

Some biosensor systems which can make real-time monitoring of fish stress (glucose levels as the stress indicator) were developed in our laboratory. However, since these systems use a button battery as the power source, it requires regular battery replacement, which leaves some problems such as unnecessary handling stress on the fish and hindrance to continuous measurement due to interruption of measurement. In this study, we tried to develop a novel biosensor system that integrated the sensor (glucose biosensor) and power source (biofuel cell) to achieve a “Barrier-free Measurement” without battery replacement.This sensor is powered by a biofuel cell that uses glucose as a substrate. On the other hand, the principle of the detection of glucose is based on quantifying glucose from the fluctuations in the current value obtained from the enzyme reaction. First, a self-powered glucose biosensor (Sensor 1) with a carbon rod as an electrode and neutral red as a mediator was developed, and the power generation characteristics and quantitative characteristics of the sensor were evaluated. The power generation characteristics were evaluated by the operating voltage calculated from the linear sweep voltammetry curve using an electrochemical analyzer. The quantitative characteristics were evaluated by gradually increasing the glucose concentration in the plasma sample of Nile tilapia (Oreochromis niloticus) and analyzing the relationship between the glucose concentration and the output current value of the sensor using a potentiostat. Furthermore, to improve the performance of the sensor, we manufactured another type of sensor (Sensor 2) that introducing a new carbon electrode material and carbon nanotubes (CNT). Then, the characteristics of the sensor during power generation and quantification were also evaluated.The power generation characteristics of Sensor 1 showed an operating voltage of 295 µV cm-2 at a glucose concentration of 100 mg dL-1, which as a virtual critical point of fish stress. Besides, it was confirmed that the output current value of the sensor increased as the concentration increased in the glucose concentration range of 46.3 to 150 mg dL-1 in the plasma sample. On the other hand, Sensor 2 showed an operating voltage of 90 mV cm-2 at a glucose concentration of 100 mg dL-1, which was about 300 times the value compared with the former sensor. Furthermore, during glucose quantification, the measurable range in fish plasma samples expanded to 200 mg dL-1, which is a relatively acceptable measurement range for fish stress monitoring. Also, the S/N ratio of the Sensor 2 was also improved by 2.5 times compared with Sensor 1. These findings are suggested that our proposed sensor system, especially Sensor 2, could be applied to fish in the future after miniaturization and intensification.