Researchers at the University of Twente, in the Netherlands, have developed an ultrasensitive sensor that could potentially be used in a handheld device to, within minutes, detect various viruses and measure their concentration. The sensor could be used to quickly screen people at hospitals and emergency clinics to control outbreaks of diseases such as SARS and the bird flu. All it would take is a tiny sample of saliva, blood, or other body fluid.
Currently available methods to detect viruses are also sensitive. But they require laborious preparation of the fluid sample and only give results after several days. Since viral diseases can spread rapidly, researchers are looking for easier, faster ways to directly detect viruses. “You want a tool on which you apply the [fluid] sample on-site and in a few minutes say whether or not the person has the SARS virus,” says Aurel Ymeti, a postdoctoral researcher in biophysical engineering and the sensor’s lead developer.
The researchers are now working with the Tiel, Netherlands-based company Paradocs Group BV to develop a commercial prototype of the sensor, which they describe online in a Nano Letters paper. The device uses a silicon substrate containing channels that guide laser light. Light enters into the substrate at one end and is split into four parallel beams. When these beams emerge at the other end, they spread out and overlap with one another, creating a pattern of bright and dark bands, known as an interference pattern, which the researchers record.
So far, the researchers have only tested the sensor for the herpes-simplex virus. On one of the four light-guiding channels, the researchers attach antibodies that bind to the virus. Then they slowly flow a saline solution of the virus along that channel. As the microbes attach to the antibodies, the interference pattern changes. The higher the concentration, the more the interference pattern shifts.
By measuring the change in the pattern for different virus concentrations, the researchers establish a fixed relationship between the two factors. Once this relationship is known, Ymeti says they can estimate the concentration of a new virus solution by analyzing the sensor’s response for a few minutes.
The researchers are also able to detect the virus in human serum, or blood plasma. This is typically harder to do than detecting the virus in a saline solution because serum contains many different proteins that can attach to the antibody and cause errors. So far, the sensor only detects the virus if its concentration in serum is high. To be useful, the improved prototype sensor should be able to accurately measure low concentrations in different body fluids.
While the sensor has only worked for the herpes virus, the researchers hope to soon demonstrate it for other viruses in order to make it widely applicable. To detect the SARS, HIV, or bird-flu virus, the researchers would have to attach antibodies specific to those viruses on the light channel. By attaching different antibodies on different light channels, the same sensor could detect multiple diseases.
Detecting various viruses with this device shouldn’t be a major hurdle, says David Gottfried, a biosensor researcher at the Georgia Tech Research Institute. Until now, no one has demonstrated a fast, portable sensor that can be used to detect viral diseases on-site. “This is one of the first demonstrations of a biosensor technique that could be [practical] for viruses, and it has the sensitivity required for early detection,” Gottfried says.
Ymeti says that the goal is to have a small microfluidics device that can test for different diseases simultaneously. He expects such a prototype to be ready within the next two years.
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