Researchers in China have reported a nanowire-based biofuel cell (NBFC) based on a single proton conductive polymer nanowire for converting chemical energy from biofluids into electricity, using glucose oxidase and laccase as catalyst. Single nanowire biofuel cell for harvesting chemical/biochemical energy can also be used for powering in vivo nanodevices such as pH, glucose or photon and biosensing sensors. The high power output, low cost and easy fabrication process, large-scale manufacturability, high 'on-chip' integrability and stability demonstrates its great potential.

In the single Nafion/poly(vinyl pyrrolidone) compound nanowire-based biofuel cell the nanowire lies on a substrate, with both ends tightly bonded to the substrate and outlet interconnects. GOx and laccase are used as catalysts in the anode and cathode region, respectively. The NBFC is immersed into a biofuel solution and two chemical reactions occur in the anode and cathode regions, creating a corresponding chemical potential drop along the nanowire, which drives the flow of protons in the nanowire and electrons through the external load. The biofuel cell of a single nanowire generates an output power as high as 0.5-3 µW in glucose solution, in human blood and the juice of a watermelon. It has been integrated with a set of nanowire based sensors for performing self-powered sensing.

The proton exchange membrane composed of Nafion film is the key component in many types of fuel cells and because of this component it is very difficult to minimise the size of a fuel cell. Researchers have fabricated Nafion nanowires, which have an enhanced performance of proton conductivity compared with Nafion film. The Nafion nanowires have a diameter about 100 nm to 1 µm, and a length of about 20 µm. However, it turns out to be very difficult to build a platinum-catalyzed fuel cell on such a small nanowire as the anode and cathode reacting area needs to be strictly separated.
Nafion nanowires can be fabricated by electrospinning method easily as long as centimeters and it is very easy to build a fuel cell based on an individual nanowires.
Biofuel cell with an enzyme pair (such as GOx and Laccase) used as catalysts can be fabricated in a miniature size as against a chemical fuel cell. In the biofuel cell the anode and cathode area need not to be separated since enzymes are very selective to the reactants, for example, the GOx will only oxidize glucose, while Laccase will only reduce oxygen in the biofluid.

The power output in glucose-containing PBS buffer solution can reach up to 2.7 µW at a power output density of around 30 µW cm-2 while the NBFC driven by blood glucose gives 0.5 µW. NBFC can work even using watermelon juice as the biofuel.
Applications

Biofuel cell has potential applications in powering in vivo wireless nanodevices. Researchers have shown that nano biofuel cell can be directly integrated with a single nanowire-based nanosensor for building a self-powered chemical - or bio-sensor. Self-powered nanosensor can be made by integrating an NBFC with a single nanowire-based pH sensor or glucose sensor fabricated using ZnO nanowires. Thus NBFC provides a new approach for self-powered nanotechnology that gives electricity in applications such as implantable biomedical devices, wireless sensors, portable electronics that are important for biological sciences, environmental monitoring, defense technology, personal electronics, electrical measurement system, data processing logic system and possibly wireless communication unit and even to power a heart cardiac pacemaker by generating power from human blood.

The website (www.engr.psu.edu/.../bioenergy/mfc_make_cell.htm) gives a clear idea to build a microbial fuel cell (MFC) using relatively inexpensive and readily available materials.

Researchers at Joseph Fourier University in Grenoble, France have successfully developed a glucose based biofuel cell (GBFC). Current devices which operate on batteries must be surgically removed when they run out of power. But these GBFCs, are about the size of a couple of pennies stuck back-to-back (much smaller than current batteries). The graphite-based cell is wrapped in a clear dialysis bag, and contains on each side different enzymes that digest oxygen from air and sugar from food, respectively. As the enzymes break down those molecules, they create an electrical charge.