The key to converting the
chemical energy is using enzymes in series at the anode.
The first enzyme breaks the
sugar, trehalose, which a cockroach constantly produces from its food,
into two simpler sugars, called monosaccharides. The second enzyme
oxidizes the monosaccharides, releasing electrons.
The current flows as
electrons are drawn to the cathode, where oxygen from air takes up the
electrons and is reduced to water.
After testing the system
using trehalose solutions, prototype electrodes were inserted in a
blood sinus in the abdomen of a female cockroach, away from critical
“Insects have an
open circulatory system so the blood is not under much
pressure,” Ritzmann explained. “So, unlike say a
vertebrate, where if you pushed a probe into a vein or worse an artery
(which is very high pressure) blood does not come out at any pressure.
So, basically, this is really pretty benign. In fact, it is not unusual
for the insect to right itself and walk or run away
The researchers found the
cockroaches suffered no long-term damage, which bodes well for
To determine the output of
the fuel cell, the group used an instrument called a potentiostat.
Maximum power density reached nearly 100 microwatts per square
centimeter at 0.2 volts. Maximum current density was about 450
microamps per square centimeter.
The study was five years in
the making. Progress stalled for nearly a year due to difficulties with
trehalase – the first enzyme used in the series.
Lee suggested they have the
trehalase gene chemically synthesized to generate an expression
plasmid, which is a DNA molecule separate from chromosomal DNA, to
allow the production of large quantities of purified enzyme from
Escherichia coli. “Michelle then began collecting enzyme that
proved to have much higher specific activities than those obtained from
commercial sources,” Lee said. “The new enzyme led