Several serious virus outbreaks, such as severe acute respiratory syndrome, have occurred in the past several years. Because viruses can spread worldwide rapidly, detecting them as quickly as possible is essential for preventing epidemics. A handheld optical sensor shows promise for quick on-site screening.Traditional methods of detection, such as polymerase chain reaction and the branched-chain DNA test, are labor-intensive, time-consuming and expensive, making them unsuitable for on-site detection. Aurel Ymeti from the University of Twente in the Netherlands and his colleagues developed an integrated Young interferometer sensor that may be able to detect several viruses within about five minutes.Figure 1. Researchers created a handheld optical sensor that can detect viruses within minutes. This photograph shows the sensor and a flow-through cuvette.Virus samples are applied to the sensing area of the 6.5-in.-long silicon chip device by removing the cover layer of the chip (Figure 1). A beam from a red diode laser enters the device through a curved optical channel waveguide (indicated in red in the figure). It travels into four integrated, parallel optical channels that branch off from the waveguide (Figure 2). Either a flow cuvette (mounted on top of the device as seen in Figure 1) or a microfluidic chip (bonded to the device) helps the sample flow through the sensing area of the channels. One of these channels is used for reference and the other three can be used to test for three viruses simultaneously by precoating each with the appropriate virus-specific antibody.Figure 2. A schematic representation of the sensor is shown here. Reprinted with permission of Nano Letters.The researchers tested their device on the herpes virus (HSV-1) by applying a sample suspended in blood. They shone a 647-nm red diode laser on the optical channel waveguide. The light traveled through the other channels, one of which was coated with an antibody for the herpes virus, to a cylindrical lens that focused the beams onto a CCD camera lens. The moment the virus attached to the antibody, the speed of light was changed in the antibody-coated channel. The camera, from Tokyo Electronic Industry Co. in Japan, displayed this change in the interference pattern and recorded the intensity — the amount of phase change — in the interference pattern. Analysis of the intensity provided information on the amount of absorbed virus particles.Ymeti explained that the device takes only about five minutes to detect the amount of virus and show what kind it is, even though the complete binding of the virus to the antibody takes about an hour.The prototype can detect three viruses at once, but he believes that further development will allow it to detect up to 20 viruses simultaneously through 20 channels.A major challenge the researchers are encountering with their prototype is finding a way to properly coat the channels with the antibodies while preventing nonspecific binding. They plan to improve this and also want to test the device on several other viruses to ensure its ability to detect multiple types simultaneously.Nano Letters, February 2007, pp. 394-397.