[tt] Yeast-powered fuel cell feeds on human blood - tech - 01 April 2009 - New Scientist

[Brian Atkins]

http://www.newscientist.com/article/dn16882-yeastpowered-fuel-cell-feeds-on-human-blood.html

Yeast cells feeding on the glucose in human blood might one day power implants 
such as pacemakers. A living source of power that is able to regenerate itself 
would eliminate the need for regular operations to replace batteries.

Now that reality is a step nearer. A team at the University of British Columbia 
in Vancouver, Canada, has created tiny microbial fuel cells by encapsulating 
yeast cells in a flexible capsule. They went on to show the fuel cells can 
generate power from a drop of human blood plasma.

Such fuel cells would be especially useful for devices, such as intraspinal 
microelectrodes for treating paralysis, which need to be implanted in places 
where replacing a battery is tricky, says Mu Chiao, who co-authored the paper 
with Chin-Pang-Billy Siu, also at UBC.
Electron theft

Conventional fuel cells rely on high-temperature catalysts such as platinum to 
strip electrons from fuels and generate a current. The idea with microbial fuel 
cells, which are being investigated as large-scale power sources is to exploit 
the wide range of low-temperature catalysts – enzymes – found in living cells.

The easiest way to do this is to simply steal the electrons produced when cells 
start to break down food. This can be done with the help of an "electron 
mediator" – a chemical small enough to pass into cells, grab some electrons, and 
diffuse out again.

The new fuel cell consists of a colony of Saccharomyces cerevisiae – the kind of 
yeast commonly used in brewing and baking – encapsulated in a fuel cell made of 
a form of silicone called polydimethylsiloxane (PDMS). The prototype is 15 
millimetres square and 1.4 mm thick.

Methyl blue – a chemical often used to stain biological samples – is used as the 
electron mediator. This steals some of the electrons produced when the yeast 
metabolises glucose and delivers them to the anode side of the cell – creating a 
small current. On the cathode side, hydrogen ions that diffuse out of the yeast 
cells combine with oxygen to create water.
Waste problem

To increase the surface area of the electrodes and thus boost the fuel cell's 
power output, the team used a silicon etching technique to create "micropillars" 
roughly 40 micrometers square and 8 micrometers high (see image).

The yeast-based fuel cell produces around 40 nanowatts of power, compared to the 
microwatt a typical wristwatch battery might produce, Chaio says. That might be 
enough power for some devices if it were coupled with a capacitor to allow 
energy to be stored. The yeast could also be genetically engineered to boost its 
power output.

This is a step in the right direction, but huge challenges remain, says Lars 
Angenent, who works on microbial fuel cells at Cornell University.

For instance, to keep the yeast cells healthy, their waste products will need to 
be removed without allowing any harmful substances to leach out into the blood 
stream. "I think people will figure this out. This is a first step," he says.

Journal reference: Journal of Microelectrical Systems (DOI: 
10.1109/JMEMS.2008.2006816)

-- 
Brian Atkins
Singularity Institute for Artificial Intelligence
http://www.singinst.org/