An optical interferometric biosensor that rapidly and accurately detects strains of avian influenza virus has been developed by researchers to better protect the poultry industry against an outbreak. Although several methods already exist to detect the lethal virus, they can require days of testing as well as expensive equipment and appropriate laboratory facilities. The avian virus is commonly found in wild bird populations but also has been found in domestic poultry. It also has started to threaten humans. Early identification is critical to controlling the extent and severity of an outbreak.The portable biosensor developed by researchers at Georgia Institute of Technology in Atlanta and at the Agricultural Research Service in Athens, Ga., can detect various viral strains, provide a reading within a few minutes and identify minuscule concentrations. The biosensor also requires no labels or reagents. The device features an interferometer with gratings that couple two beams of light from a Hitachi laser diode into a waveguide. Specific antibodies were immobilized on the waveguide surface, and one beam traveled under the antigen-specific antibody, while the second one traveled under a nonspecific antibody in the reference channel. An electric field associated with the light beams extended above the waveguide and detected changes caused by antibody-antigen interactions. After interacting with the sample, the light was coupled out of the waveguide and combined with a simple lens. The resulting interference patterns were imaged onto a Logitech CCD detector. The biosensor detected two strains of avian influenza (H7N2 and H7N3) that previously have infected poultry. A third strain was used as a control. The researchers said that viral concentrations as low as 0.0005 hemagglutination units per milliliter were detected with the interferometric biosensor. The work was published in the October issue of the journal Analytical and Bioanalytical Chemistry.