THE molecules that make muscles contract could give an early warning of a
biological weapons attack. A team of Australian researchers is using the
molecules to develop a chip-based bioweapons detector small enough to fit on a
wristwatch.
When a muscle contracts, filaments of two proteins, actin and myosin, slide
past each other. The researchers say that if you attach myosin molecules to a
biochip, you can use the movement of the adjoining actin molecules to detect
whether biowarfare agents such as anthrax are present.
At the moment, bacteria and viruses are usually identified using laboratory
equipment the size of a large fridge, or with tests that take days. But a quick
result is vital in germ warfare, and biodetectors must be light and portable
enough to be taken to the scene of a possible attack.
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To produce such a device, one of the first problems that Dan Nicolau of
Swinburne University of Technology in Melbourne and Cris dos Remedios of the
University of Sydney had to overcome was getting thousands of actin and myosin
molecules lined up in the same direction. They did this by embedding the myosin
molecules in microscopic channels on a polymer chip. “Proteins attach to
surfaces as they like, not as we like, so we had to engineer the surfaces again
and again until we found the right composition,” says Nicolau.
In the end, the team coated their chip with a polymer that doesn’t attract
proteins, and etched tracks into it with a laser. This exposed a new surface
that the myosin sticks to.
Each of the biodetectors will contain hundreds of tracks, and each will carry
thousands of actin and myosin molecules. In the right chemical environment actin
molecules continuously move along the myosin molecules.
The researchers plan to detect biological weapons by attaching special
antibodies to the actin molecules. These antibodies stick to proteins on the
surface of biowarfare agents, such as anthrax. When the antibodies bind to the
agents they will stop the actin molecules from moving along the myosin-lined
channels.
Nicolau and dos Remedios are now looking at different ways to detect when the
actin molecules have come to a sudden stop. One possibility, says Nicolau, is to
attach tiny magnetic beads to the actin
(see Figure). The researchers have
already shown that the beads do not slow down the actin molecules, and when the
actin is moving the beads will induce an electric current in an induction coil.
The next step is to build the circuits needed to amplify these signals.
An alternative way to detect when the molecules come to a halt would be to
use an alloy that exhibits “giant magnetoresistance”. Moving the magnetic beads
past the alloy in the presence of a magnetic field would cause a huge change in
its resistance.
The researchers presented their findings at a meeting in Hawaii last month
sponsored by the US Defense Advanced Research Projects Agency. “It’s a
tremendous idea,” says Bruce Cornell, chief scientist for AMBRI, a Sydney-based
biotech company that is developing its own biosensors. “They’re attempting to
use molecules to detect molecules. They’re dealing with things on the same size
scale, so it has the potential to be extremely sensitive.”
Piotr Grodzinski, a microfluidics expert at Motorola in Tempe, Arizona,
praised the idea. “There’s a lot of creative thinking that went into this
development,” he says. Nicolau and dos Remedios plan to have a working prototype
of the detector in two years’ time.