Scientists have developed a glucose-powered biofuel cell that uses electrodes made from cotton fibre, and may help power implantable medical devices such as pacemakers and sensors.
The fuel cell, which provides twice as much power as conventional biofuel cells, could be paired with batteries or supercapacitors to provide a hybrid power source for the medical devices, said researchers from the Georgia Institute of Technology in the US.
The researchers used gold nanoparticles assembled on the cotton to create high-conductivity electrodes that helped improve the fuel cell's efficiency, according to the results published in the journal Nature Communications.
That allowed them to address one of the major challenges limiting the performance of biofuel cells -- connecting the enzyme used to oxidise glucose with an electrode.
A layer-by-layer assembly technique used to fabricate the gold electrodes -- which provide both the electrocatalytic cathode and the conductive substrate for the anode -- helped boost the power capacity to as much as 3.7 milliwatts per square centimetre.
"We could use this device as a continuous power source for converting chemical energy from glucose in the body to electrical energy," said Seung Woo Lee, an assistant professor at Georgia Tech.
"The layer-by-layer deposition technique precisely controls deposition of both the gold nanoparticle and enzyme, dramatically increasing the power density of this fuel cell," said Lee.
Fabrication of the electrodes begins with porous cotton fibre composed of multiple hydrophilic microfibrils -- cellulose fibres containing hydroxyl groups.
Gold nanoparticles about eight nanometres in diameter are then assembled onto the fibres using organic linker materials, researchers said.
To create the anode for oxidising the glucose, the researchers, including those from Korea University, apply glucose oxidase enzyme in layers alternating with an amine-functionalised small molecule known as TREN.
The cathode, where the oxygen reduction reaction takes place, used the gold-covered electrodes, which have electrocatalytic capabilities.
The porosity of the cotton allowed an increase in the number of gold layers compared to a nylon fibre.
"Cotton has many pores that can support activity in electrochemical devices. The cotton fiber is hydrophilic, meaning the electrolyte easily wets the surface," said Yongmin Ko, a visiting faculty member at Georgia Tech.
Beyond improving the conductivity of the electrodes, the cotton fibre could improve the biocompatibility of the device, which is designed to operate at low temperature to allow use inside the body.
Implantable biofuel cells suffer from degradation over time, and the new cell offers improved long-term stability.
"We have a record high power performance, and the lifetime should be improved for biomedical applications such as pacemakers," Lee said.
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