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Optical biosensors help spot bird-flu

01 Sep 2005

A low-cost and portable optical waveguide sensor could help control avian influenza during an outbreak.

An optical waveguide sensor being developed by scientists at Georgia Tech Research Institute, US, could offer a fast, portable and reliable way to identify poultry infected with avian influenza (AI). With the only way to stop the infection spreading being a complete cull of birds that may have been exposed to the virus, the sensor could aid the control of an AI outbreak.

Current methods of identifying infected flocks suffer from a series of disadvantages such as high costs, long processing times and low sensitivity.

Georgia Tech senior research scientist David Gottfried and colleagues realised there was a real need for a low-cost field-deployable biosensor that gave both rapid and sensitive results. The team had a background in developing sensors to detect food-borne pathogens such as Salmonella, which could easily be adapted to study strains of AI.

The biosensor uses a planar waveguide coated with antibodies in tandem with interferometry to detect the presence of a particular strain of AI. A grating couples light from a 670 nm, 5 mW, laser diode into the waveguide. This is split between a sensing and a reference channel and recombined in a Mach-Zender interferometer.

When an antigen binds to an antibody in the sensing channel, this causes a change in refractive index which shifts the interference pattern. This change alerts the team to the strain of the virus and allows them to calculate its concentration.

The researchers use silicon nitride waveguides on a glass substrate that measure 16 x 33 mm. These are fabricated in-house by etching the grating couplers into the substrate and using PECVD to deposit the nitride layer.

"We are currently working with a single strain, however multiple strains can be detected using a cocktail of antibodies or by using a multi-interferometer waveguide," Gottfried told Optics.org. "Our current waveguides have a single interferometer but we have prototypes for 8 interferometer chips."

Although at a proof-of-principle stage, Gottfried is pleased with the initial results. "We are still early on in proving the concept and its sensitivity, selectivity and reproducibility but the results are very promising," he said.

Gottfried added that the team is interested in commercialising the research and is looking for potential collaborators.

Jacqueline Hewett is technology editor on Optics.org and Opto & Laser Europe magazine.

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