Biochip detects salmonella, E. coli in real-time

Biochip detects salmonella, E. coli in real-time
KINGSTON, R.I. —: University of Rhode Island researchers have invented a technology that uses inexpensive fiber-optic probes to detect pathological bacteria in foods in real-time. Currently, food samples must be sent to a lab for testing, and obtaining results takes several days. A fiber-optic probe, however, can be inserted into foodstuffs at the processing plant to test levels of bacteria in about an hour.

"Basically you just stick the optical fiber into the food, and our software reads out how much of a specific bacteria is present," said Phil Pavarnik, a researcher working on the project.

Each year, more than 75 million citizens in the United States become ill from food poisoning; of those, 325,000 must be hospitalized, and 5,000 die. Detecting salmonella and E. coli before food is shipped could save those lives, plus millions of dollars in medical expenses.

To combat food poisoning, the University of Rhode Island joined an ongoing national effort to develop biosensors that would read out pathogen levels in real-time. After 10 years of work, the university recently announced its first ready-to-use biosensor technology.

Fiber dip

Unlike other efforts, such as one at Purdue University, the Rhode Island approach couples biosensor techniques with fiber-optic technology. By dipping the end of an optical fiber into the food to be tested, the new system can accurately detect and quantify the levels of pathogen present. "If we could get the 6,000 U.S. meat and poultry plants to test their foods with biosensors, they could have their results back before it leaves the plant, instead of several days later," said University of Rhode Island professor A. Garth Rand.

Rand teamed up a decade ago with Stephen Letcher, professor of physics, and Christopher Brown, professor of chemistry, to establish the Fiber Optic and Biosensor Research Group at the university. Pavarnik helped more recently to develop the fiber-optic-based food pathogen sensor.

The group has been funded by the U.S. Department of Agriculture for the last eight of its 10 years. It claims its interdisciplinary approach — melding physics, chemistry and agriculture — was the key to its winning funding and to the success of its research effort. "Our group is uniquely qualified. There was no way to solve this problem without our careful interdisciplinary approach," Rand said.

Most other biosensors must be immersed in the food to be tested, but the Rhode Island technique employs optical fibers to isolate the food from the sensor. First, microscopic beads called microspheres are prepared by coating them with antibodies that bind to the pathogen cells to be tested. The microspheres are then mixed into a sample of the food, and pathogens begin immediately to bind to the spheres.

After about an hour, a fiber-optic probe can be inserted into the food to measure its pathogen levels. Each microsphere is labeled with a fluorescent dye so that it can be easily counted with software that reads the fiber-optic probe signal. Different pathogens can be tested simultaneously by mixing in different microsphere beads.

90-second answers

The beads are magnetic, simplifying the process of focusing them in front of the optical fiber. A laser-based measurement algorithm running on data from the optical fiber enables the biosensor to measure the levels of each selected pathogen for which a microsphere bead was previously mixed. The measurement process takes only 60 to 90 seconds (after the beads have been mixed in for an hour).

The researchers claim that their technology is ready for commercialization, but they caution that further engineering refinements may delay product release by a couple of years. The University of Rhode Island is working with Pierson Scientific Associates (Andover, Mass.) to develop portable biosensor prototypes under a Small Business Technology Transfer grant from the National Science Foundation.

The researchers also have received funding from the U.S. Army's Natick Labs to help detect pathogens in K rations — dried foods that are often stored for years before use.

"The Army wants a quick and easy way to detect pathogens in low-moisture foods that are stored in various environments around the world," Rand said. Here the researchers are working on a membrane biosensor coated with antibodies and enzymes that catch bacteria with which they come in contact.

And for the long term, the researchers are planning a handheld surface-scanning system, similar to a laser scanner, that can be held over any food to detect pathogens without touching it.