Abstract
The changes in blood glucose levels are a key indicator of fish health conditions and are closely correlated to their stress levels. Here, we developed a self-powered glucose biosensor (SPGB) consisting of a needle-type enzymatic biofuel cell (N-EFC), which was operated underwater and connected to a charge pump integrated circuit (IC) and a light emitting diode (LED) as the indicator. The N-EFC consisted of a needle bioanode, which was inserted into the caudal area of a living fish (Tilapia) to access biofuels, and a gas-diffusion biocathode sealed in an airtight bag. The N-EFC was immersed entirely in the water and connected to a charge pump IC with a capacitor, which enabled charging and discharging of the bioelectricity generated from the N-EFC to blink an LED. Using a smartphone, the glucose concentration can be determined by observing the LED blinking frequencies that are linearly proportional to the blood glucose concentration within a detection range of 10–180 mg/dL. We have successfully demonstrated the feasibility of the SPGB used to continuously monitor the physiological status of free-swimming fish treated with cold shock in real time. The power generated by a free-swimming fish with an N-EFC inserted into its caudal area, swimming in a fish tank with a water temperature (Tw) of 25 °C, exhibited an open circuit voltage of 0.41 V and a maximum power density of 6.3 μW/cm2 at 0.25 V with a current density of 25 μA/cm2. By gradually decreasing Tw from 25 °C to 15 °C, the power generation increased to a maximum power density of 8.6 μW/cm2 at 0.27 V with a current density of 31 μA/cm2. The blood glucose levels of the free-swimming fish at 25 °C and 15 °C determined by the blinking frequencies were 44 mg/dL and 98 mg/dL, respectively. Our proposed SPGB provides an effective power-free method for stress visualization and evaluation of fish health by monitoring a blinking LED through a smartphone.
Highlights
Inadequate breeding environments, such as overcrowded farming, the deterioration of water quality and extremely cold/hot weather can induce stress in fish and affect their development and health [1]
We have successfully demonstrated the feasibility of the self-powered glucose biosensor (SPGB) used to continuously monitor the physiological status of free-swimming fish treated with cold shock in real time
Rather than use an electrochemical analyzer to analyze the glucose concentration of a free0.1 the SPGB to provide a simple, power-free and2 useful stress visualization swimming fish, we designed to evaluate fish health by monitoring light emitting diode (LED) blinking with a smartphone
Summary
Inadequate breeding environments, such as overcrowded farming, the deterioration of water quality and extremely cold/hot weather can induce stress in fish and affect their development and health [1]. Stressed fish become immunocompromised causing mass mortality owing to the decrease in resistance to infectious diseases. The change in blood glucose levels, which closely correlate to stress levels in fish and represent the status of respiratory or nutritional disturbance, is a blood indicator that can help determine fish health conditions [2]
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