Miniature enzymatic fuel cells for self powered healthcare sensors

Self-powered wearable biodevices are highly attractive for a number of applications, including non-invasive detection of biomarkers and fitness monitoring. Enzymatic fuel cells (EFCs) hold great potential for the development of such devices. This particular type of fuel cells uses redox enzymes as catalysts to convert organic substrates, such as carbohydrates, into useful electricity at body temperature. In the past few years, electricity generation from human physiological fluids via EFCs has been reported, which proved the possibility to harvest energy from tears, serum and saliva. Through a careful choice of the enzymes used, EFCs can work as effective amperometric biosensors for target biomarkes. We have developed innovative miniature flow-through glucose/oxygen enzymatic fuel cells for continuous power generation. The EFCs use highly-porous gold (hPG) as electrodes. hPG is characterised by a very high specific surface area, with a pore size distribution ranging from the micro to the nano scale. This property, in combination with high conductivity and biocompatibility, makes hPG electrodes the ideal support for enzyme immobilisation and allows a very good electrical communication between the electrode and the enzyme, with no need for external electron mediators.
To scale-up the power density, we developed a cascade of EFCs embedded in a compact and handy single channel device. To prove its use with a physiological fluid, the device was tested for the first time with transdermal extracts obtained by iontophoresis. The miniature EFCs generate power outputs in the orders of 1-5 μW cm-2. Glucose detection in the sweat range (5.6 and 2,200 µM) was demonstrated, thus paving the way for self-powered painless glucose monitoring applications. We also proved for the first time that EFCs can be used to detect the neurotransmitter acetylcholine, identified as a biomarker for the Alzheimer’s disease, when acetylcholinesterase is used as the anode catalyst.