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THE SOUND of a flying virus could soon give doctors quicker, cheaper
diagnoses. The trick is to pick up the telltale noise a virus makes as it breaks
free from a vibrating quartz crystal.

Matthew Cooper and his team at Cambridge University coat a crystal with
antibodies to a test virus and introduce the virus itself so that it binds to
the antibodies. An electric current is applied to make the crystal vibrate. Then
the researchers turn up the voltage to make the crystal vibrate faster until a
virus particle is shaken off, making a tiny sound as it goes. Because different
types of virus form bonds of different strengths, the voltage at which the
researchers hear the bonds snap should reveal the identity of the virus.

鈥淚t鈥檚 shaking pretty fast and hard. We are talking about accelerations about
10 million times the force of gravity,鈥� says Cooper. 鈥淲hen the bond snaps, it
releases energy and some of that energy is released as sound. The tricky bit is
that we use the same quartz crystal as a microphone to detect that sound,鈥� he
says. The system is so sensitive it can pick up even a single virus particle by
its sound.

For their trials, the researchers coated the crystal with antibodies that
bind to a protein on the surface of a strain of herpes simplex virus. Ultimately
they hope to put antibodies to several different virus strains onto the same
crystal and test for them all in one session.

There are still a few problems to iron out, cautions Cooper. For instance,
blood contains proteins that might interfere with the viruses binding to
antibodies on the crystal surface. But ultimately, Cooper hopes to turn the
crystal technique into a cheap, fast and portable diagnosis kit that doctors
could use in hospitals or surgeries.

Detecting viruses can be costly and time-consuming with existing techniques.
One method, called ELISA, looks for the antibodies the immune system pumps out
in response to an infection. ELISA is accurate, but is not always sensitive.
With another method, PCR, a bit of viral DNA or RNA is isolated and copied to
reveal the virus鈥檚 identity. PCR is fast and sensitive, but expensive, and prone
to contamination.

鈥淭his new device seems to combine the advantages of ELISA with the speed and
sensitivity of PCR,鈥� says immunologist Paul Parren of The Scripps Research
Institute in La Jolla, California.

鈥淚t promises to be a really useful device that could detect viruses in the
field, in remote locations, or even in hospitals, and could do it more cheaply
than is done right now,鈥� says Parren.