Microchip Sensor Detects Bacteria

April 07, 1998

ITHACA, N.Y. -- Detecting potentially deadly bacteria in food, the water supply or on the battlefield before it does damage has never been reliable or fast enough to prevent death, illness or economic loss. As just one example, last year a Columbus, Neb., beef-processing plant was forced to recall 25 million pounds of hamburger when less than a speck of bacteria was detected.

But now Cornell University researchers have merged the fields of nanofabrication and biology to produce a simple but effective means to detect harmful bacteria. New biosensors can detect minute quantities of bacteria, from the slaughterhouse to the restaurant, and send up a red flag when there's a problem.

The biosensors, developed by Harold Craighead, professor of applied and engineering physics, in collaboration with Carl Batt, professor of food science, are simple in concept and arose from technology that is the mainstay of the microelectronics industry. The sensors capture bacteria in a regular, repeating pattern and, similar to the UPC bar code used in a supermarket, can be read using a laser beam.

"It's like a printing press," says Batt. "By stamping antibodies on the surface, the bacteria will be bound to the sensor, and they then form a pattern that can be read with a laser. It is a very fast, direct method for detecting bacteria."

The research is reported in the latest issue of Analytical Chemistry (March 15). The senior author on the paper with Batt and Craighead is Pamela St. John, a former postdoctoral fellow at Cornell. The other authors are Robert Davis, a Cornell postdoctoral fellow, John Czajka, a recent graduate student in food science, and Nathan Cady, an undergraduate in biology.

Using Cornell's nanofabrication facility, the researchers made small-scale rubber stamps imprinted with diffraction gratings, which are the patterns of the lines of bacteria-seeking antibodies. In this case the Cornell team targeted E. coli O157:H7, a deadly pathogen that has been linked to deaths resulting from the contamination of tainted hamburger. These patterns were then stamped on the surface of silicon, the same material used in computer chips, providing a sticky surface for bacteria to cling to.

To detect E. coli on the sensor, the silicon chip was illuminated with a laser, and the laser light was diffracted at a particular angle. The more bacteria bound to the silicon surface, the greater the diffraction intensity.

The researchers say that this gives an instant reading of the level of bacterial contamination. The laser reader, they say, could be incorporated into a simple, hand-held device to be used anywhere that bacteria are a contamination threat. Similarly, the silicon chips could be placed at strategic points on a food production line or other sensitive area and tied to a central computer to monitor bacterial contamination.

The use of nanotechnology to create a specific pattern on the surface of the silicon, say the researchers, is a demonstration of how methods developed in the microelectronics industry will have a broad impact on biological problems. "This is just one example of the possible use of nanofabrication technology for biological applications," says Craighead.

Batt points to the enormous challenge of detecting bacteria at every stage in the food processing industry. "As history has shown us, if a small colony of bacteria gets into the system, the cost, both in health and economic terms, can be enormous," he says. He notes that hospital-borne infections, battlefield threats, even community-acquired infectious disease are also applicable to this new biosensor technology.

"Bacterial contamination takes thousands of lives, sickens millions and costs the health care industry billions of dollars a year," says Batt. "If we had an early warning system, such as these biosensors could provide, we would be aware of the problem and able to attack it much more efficiently."

Cornell University

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