The biofuel cell arrays are laid out in series and parallel. These cells consist of enzymes in the electrodes that produce an electric current when it reacts with lactate. (Image Credit: Tokyo University of Science)
Electronics and biosensors commonly serve as health monitoring devices, but their batteries have limited power. This makes it difficult to use for long periods without recharging. Scientists at the Tokyo University of Science (TUS) developed a biofuel cell array that uses lactate in human sweat to generate electricity, keeping a biosensor and wireless communication devices powered for a short time.
The biofuel cell array's appearance is similar to a bandage that's worn on the arm or forearm. It's comprised of water-repellent paper substrate, which contains the biofuel cells that are laid out in series and parallel. All these cells have enzymes in the electrodes that generate an electric current as it reacts with lactate. Then, the energy flows to a current collector made of conducting carbon paste.
This isn't the first lactate-based biofuel cell ever created. In 2017, Binghamton University researchers produced a stretchable battery prototype capable of transforming human sweat into energy.
The team says this new development is unique compared to other lactate-based biofuel cells. One reason is based on the device's fabrication process: screen printing, making it ideal for affordable mass production. This was achieved by carefully choosing materials and an ingenious layout. Instead of using silver wires as conductive paths, these biofuel cells deploy porous carbon ink.
Even more advantageous is the delivery of lactate to each cell. Paper layers accumulate the wearer's sweat and transport it to the cells simultaneously via the capillary effect. This effect is the same as water moving quickly through a napkin as it comes in contact with a wet surface.
Those advantages allow the biofuel cell arrays to deliver energy to electronic circuits. Dr. Shitanda, Associate Professor from Tokyo University of Science, says, "In our experiments, our paper-based biofuel cells could generate a voltage of 3.66 V and an output power of 4.3 mW. To the best of our knowledge, this power is significantly higher than that of previously reported lactate biofuel cells." To prove its applicability for wearable biosensors and electronics, the team fabricated a self-driven lactate biosensor. Not only does the device charge itself with lactate and measure lactate concentration in sweat, but it also relays the measurements in real-time to a smartphone through a low-power Bluetooth device.
Lactate is a crucial biomarker that indicates how intense physical exercise becomes in real-time for athletes and rehabilitation patients. The biofuel cell arrays provide power to wearable lactate biosensors and wearable electronics. "We managed to drive a commercially available activity meter for 1.5 hours using one drop of artificial sweat and our biofuel cells," explains Dr. Shitanda, "and we expect they should be capable of powering all sorts of devices, such as smartwatches and other commonplace portable gadgets."
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