ARCHIVED - Photonic wires to detect pathogens
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October 01, 2008— Ottawa, Ontario
Thanks to recent breakthroughs by NRC researchers, a technology now used in optical telecommunications may soon provide the first working generation of hand-held biosensors — sensors to quickly and reliably detect contaminants in food or infectious agents in human tissue.
The new photonic-wire evanescent field (PWEF) sensor technology would replace fluorescent labelling, which is found in most biosensors today but requires a multi-step laboratory process of hours or days. Both methods can analyze a biological sample to determine the presence of a target molecule, such as a piece of DNA or a marker molecule that betrays the presence of a specific pathogen. But PWEF promises a simpler, more field-efficient version — one that analyzes using light, not chemicals.
"The implications are very important for the food industry, medical science and drug research," says Dr. Siegfried Janz, who leads the optoelectronic devices group at the NRC Institute for Microstructural Sciences (NRC-IMS). "We would like to develop an optical sensor that could go into a food inspector's briefcase or on the shelf at a medical lab, scan a food or blood sample for molecules that shouldn't be there, and give an accurate read-out instantly." Other potential applications may include hazardous-gas detection and routine industrial-process monitoring.
|A 10-sensor biochip, using NRC's PWEF technology. Light from the optical fibre (left) is distributed through silicon waveguides to 10 PWEF sensors, while a fluid sample flows across them. Output signals are monitored continuously by the photodetector array (right).|
Photonic wire technology is being hotly pursued by the computer industry and academic researchers worldwide. Miniscule photonic-wire "waveguides", less than a micrometre wide, can be etched into the surface of a silicon chip. When coupled to a light source, the waveguides carry a tiny beam of light, much as a wire carries an electrical current. This light can be used as a signal in computer circuitry, but at NRC-IMS, a silicon photonics team is exploring a very different application: PWEF's valuable potential for revealing hidden molecules.
NRC's sensor technology sends light along the interface between the silicon and the liquid sample that sits atop the sensor. The light "searches" for a target molecule — for example, the telltale molecule of a protein unique to certain bacteria. If it hits the target, this information is interpreted by the sensor's photodetector. Once a sensor of this type is perfected, the technician would need only to pour in the sample and read the results.
The NRC-IMS team scored a breakthrough last fall while focusing on the ability of photonic wires to steer light around micrometre-wide hairpin turns. The fact that the wire can be bent into dense, serpentine patterns, with a relatively long length of wire occupying a tiny space, proved the key to a practical new sensor design.
"To detect trace amounts of a molecule, the waveguides need to carry light through millimetres or even centimetres of sample material," Dr. Janz explains. "In the world of nanotechnology, such distances are enormous. Our challenge was to make the track long while keeping the sensor small. People knew already that you could make tiny bends in silicon photonic wire. But we were the first to fold PWEF waveguides into a tiny space inside a biosensor."
The NRC-IMS researchers are now focusing on building biochips that could be used routinely in the field or clinic. Their work is part of a Genomics and Health Initiative program that involves five NRC institutes working together to demonstrate how pathogen detection can be revolutionized by new biosensing paradigms at the micron scale.
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National Research Council of Canada
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