An entirely new concept in how biosensors work has been developed by Israeli and German scientists. Rather than having dangling wires providing electrical power to a sensor unit, the researchers have developed an onboard biofuel cell to drive the sensing process and retrieve a signal. The new approach to biosensors will make them perfect for invasive sensing, such as devices that are inserted under the skin to monitor sugars and metabolites or for remote environmental sensing.
By exploiting the chemical-to-electrochemical energy transformations occurring in biofuel cell elements Itamar Willner and Eugenii Katz at The Hebrew University of Jerusalem working with Andreas Bückmann at the Society for Biotechnology Research in Braunschweig have found they can preclude entirely the need for an external power supply in a biosensor.
Several research teams have endeavoured to make electrical contacts between redox enzymes and their electrode supports in a biosensor. According to Willner, the tethering of electroactive relays to redox proteins and immobilizing redox proteins in electroactive polymers have been successful routes to this end. In 1996, he and his team first reported that they had made an effective electrical contact of flavoenzymes on electrodes by structurally aligning the enzyme on the electrodes through a flavin adenine dinucleotide (FAD) monolayer.
By including an anode and cathode consisting of the enzyme glucose oxidase which is coated on the monolayer electrode and a second electrode with the cytochrome c/cytochrome oxidase system, the sensor can power itself. The fuel — glucose from the biological fluid is oxidized by oxygen and yields electrical power. Various biological analytes can be detected without external power because the concomitant reaction of the glucose in the sample produces adequate electricity. A related tailored anode configuration consisting of lactate dehydrogenase assembled on an electrically contacted nicotinamide adenine dinucleotide cofactor-monolayer was used to analyse lactate.
Such a fuel cell arrangement operates at very low efficiency, however, which would seem to be a hindrance but Willner and his team reckon that adequate electrical energy produced provides the power to probe the sensing event and so detect an analyte of interest. They also point out that low electrical power output is actually an advantage in the sensing process because it precludes redox reactions that would otherwise produce a signal from any contaminants present that might interfere at the electrode.
The team is now working on biofuel-powered sensors for alcohol, fructose, and amino acids.