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.