ARCHIVED - Optical telecom chips to power biomedical research

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February 05, 2010— Ottawa, Ontario

NRC scientists are adapting silicon chips used in modern optical telecommunications networks into a new role — as sensitive, molecular biosensors to detect disease pathogens and identify promising new drugs. 

NRC anticipates using the silicon-based sensors to, among other things, test antibody-antigen interactions, detect biomarkers that warn of cancer or recent heart attacks, and detect sections of DNA molecules that fingerprint, for example, drug-resistant "hospital super bugs" or food-poisoning bacteria. 

Dr. Siegfried Janz leads the team at NRC that is adapting silicon chips for use as biosensors. The sensors could speed up analysis of molecules for developing drugs and detecting disease.

Dr. Siegfried Janz leads the team at NRC that is adapting silicon chips for use as biosensors. The sensors could speed up analysis of molecules for developing drugs and detecting disease.

The sensors may also help pharmaceutical researchers develop more affordable drugs — and more quickly. The current process involves testing huge banks of potential drug molecules by observing the performance of each molecule in hundreds or thousands of parallel interactions to see which ones show promise. Better sensors would speed things significantly. 

Researchers at the NRC Institute for Microstructural Sciences (NRC-IMS) in Ottawa are working on the project with other NRC experts under the umbrella of the NRC Genomics and Health Initiative

NRC-IMS has researched silicon photonics for telecommunications for about 15 years. Around 2000, when optical telecommunications technology was maturing, NRC-IMS began to seek new research areas, says Dr. Siegfried Janz, leader of the sensor development team. 

Silicon photonics was originally developed to build the optical switches and routers needed to direct tens or hundreds of optical data streams in modern telecommunications and computer networks. These optoelectronic chips use photonic wires — thin strands of silicon less than the width of a light wave — as waveguides that direct and manipulate optical data streams passing through the chip. NRC researchers realized the photonic wires could be adapted to make sensitive probes that measure the molecular properties of biochemical mixtures. When photonic wire sensors were combined into sensor arrays on a single chip, each sensor could be monitored using techniques already well established in telecommunications networks. The NRC team tested its first working biosensor chip, holding just a half-dozen sensors, in mid-2009. 

"The key point is that we're trying to detect molecules by how they interact with the light that's travelling through the waveguides," says Dr. Janz. "The name of the game is to have as much light as possible concentrated in an extremely thin layer at the surface of the waveguide. It turns out that silicon waveguides concentrate the light right at the surface." 

Older molecular sensing devices that concentrate a thin layer of light are already standard in many university and pharmaceutical labs. But these devices are about the size of small apartment refrigerators and only a few specialized manufacturers make them. 

A sensor on a silicon chip surface. When the sensor comes in contact with a sample liquid, molecules in the liquid bind to the spiral threads of silicon (the waveguide). This changes the speed of light travelling through the waveguide, and the change can be measured to reveal the molecules present in the liquid.

A sensor on a silicon chip surface. When the sensor comes in contact with a sample liquid, molecules in the liquid bind to the spiral threads of silicon (the waveguide). This changes the speed of light travelling through the waveguide, and the change can be measured to reveal the molecules present in the liquid.

PWEF arrays turn out to be more sensitive and less expensive. The chips can be produced cheaply in most existing silicon chip foundries, and the desktop-PC or shoebox-sized readers that they plug into can be assembled off-the-shelf from the parts inventories of telecom manufacturers. "The cost per chip is just a few dollars," says Dr. Janz. 

A single sensor in an array is 100 microns across, he adds, so in large-scale commercial versions, a chip smaller than your baby fingernail could hold an array of 100 or more identical sensors. Biologists could then conduct multiple tests by "painting" different molecules onto each sensor and observing the results for each one. 

A team at the NRC Institute for Biological Sciences is now automating the production of biosensor array chips. They're programming a robotic spotting machine — resembling a micro-scale inkjet printer — to squirt a tiny drop of different biochemical mixtures onto different sensors in order to run multiple tests in parallel and confirm a specific molecule's presence. Taken together, the sensors could quickly tell researchers whether particular DNA, bacteria or antibody molecules are present, with a high degree of certainty.

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National Research Council of Canada
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