Crystal listens for telltale sounds of virus

After successfully testing a device that can hear the movement of a single virus from a drop of fluid, researchers envision a handheld instrument that could detect viral illnesses such as foot-and-mouth disease and Ebola.

A vibrating quartz crystal can hear a virus popping off the crystal’s surface. Cooper et al./Nature Biotechnology

The investigators suggest that their acoustic detector could be quicker and more economical than current assays used to identify viruses in blood, saliva, and other bodily fluids. Many of those tests employ expensive enzymes and take days to perform.

The new device depends upon a small piece of quartz crystal similar to the billions of crystals used every year in televisions, VCRs, computers, and phones. The researchers coat one surface of their coin-size quartz disk with antibodies specific to whatever virus they want to detect.

To find viruses in a fluid, the investigators place a drop onto the crystal and allow about 40 minutes for the antibodies to snag any viruses present.

They then shoot electricity through the crystal, causing it to vibrate back and forth horizontally and repeatedly shift the position of any virus attached to an antibody.

As the voltage applied to the crystal increases, its vibrations speed up, and the viruses shift up to 10 million times a second. This exposes them to forces of up to about 10 million times that of gravity, says Matthew A. Cooper of the University of Cambridge in England.

When the forces become too strong for the bonds that join a virus and an antibody molecule, the virus breaks free and releases energy, some of it as a high-pitched sound. Cooper compares the sound to the snap heard when a twig breaks after being bent.

The quartz crystal also serves as a microphone that picks up the viral snap. “We use the crystal to both shake and detect” the virus, says Cooper.

Moreover, since all the individual viruses pop off at the same vibrational frequency, the strength, or loudness, of that acoustic signal provides a direct measure of the number of viral particles in the tested sample, the researchers report in the September Nature Biotechnology.

The scientists tested their device on herpes simplex virus, a relatively innocuous pathogen that can infect the mouth, eyes, and genital tract.

“It’s a surrogate for more pernicious viruses such as HIV or hepatitis B,” says Cooper.

In a series of trials, the investigators confirmed that they could detect the virus in a water solution and in serum, the cellfree portion of blood.

Frances S. Ligler, who studies biosensors at the Naval Research Laboratory in Washington, D.C., notes that the crystal’s sensitivity dropped significantly when the investigators tested serum. “It remains to be determined whether the detection method will be very sensitive or quantitative in the presence of highly variable patient sera,” she says.

“It’s always a big jump going from a lab situation to a real clinical sample,” agrees Cooper, who notes that his group plans to work soon with a local hospital to test patients’ blood samples for a variety of viruses.

The researchers have also set up a company to commercialize their invention. Since the device’s electronics can be miniaturized easily, the researchers would like to build a portable unit for detecting pathogens outside of a laboratory setting.

Such an instrument would help veterinarians and physicians monitor outbreaks, suggests Cooper. It would have been useful, he notes, to public health officials in England who recently sought to stem the spread of the virus that causes foot-and-mouth disease in animals.

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