"The ability to distinguish this one species from all others makes this a very powerful sensor. No other sensor today can do that," he said.
The sensor also is selective enough to recognize cells of L. monocytogenes when other types of foodborne contaminants, such as salmonella or E. coli, are present.
Known as an "optical biosensor," the device uses light to detect the presence of a target organism or molecule. Bhunia and his colleagues have been developing this sensor for three years and demonstrate its function in the current issue of the journal Applied and Environmental Microbiology.
The sensor is made of a small piece of optical fiber - a clear, solid, plastic material that transmits light through its core. The fiber is coated with a type of molecule called an antibody, which specifically recognizes L. monocytogenes and captures it, binding it to the fiber. When the fiber is placed in a liquid food solution, any L. monocytogenes in the sample will stick to the fiber.
The presence of L. monocytogenes is verified by the addition of a second antibody, which not only recognizes L. monocytogenes but also carries a molecule that produces a fluorescent glow when exposed to laser light. This antibody attaches to the L. monocytogenes bound to the fiber and acts as a flag, signaling the pathogen's presence when laser light is passed through the liquid.
Bhunia expects the sensor to be ready for industrial use in another year.
Many tests currently in use require a high concentration of pathogen cells - typically from 1 million to 10 million cells per milliliter of fluid, Geng said. The tests also rely on a process known as "enrichment," which occurs when a sample believed to be contaminated grows for a period of time in a nutrient broth to allow any pathogen cells present to multiply.
The enrichment process increases the concentration
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Contact: Jennifer Cutraro
jcutraro@purdue.edu
765-496-2050
Purdue University
5-Oct-2004