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Real-time listeria biosensor prototype

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The prototype listeria biosensor chip is a little smaller than postage stamp. Dr. Carmen Gomes, Texas A&M AgriLife Research engineer, said even at this early stage of development, the sensor can detect as little as one bacterium in about one ounce of food product. (Texas A&M AgriLife Communications photo by Robert Burns)

Dr. Carmen Gomes, AgriLife Research engineer with the Texas A&M University and Dr. Eric McLamore at the University of Florida at Gainesville have developed a biosensor that can detect listeria bacterial contamination within two or three minutes. “We hope to soon be able to detect levels as low as one bacteria in a 25-gram sample of material – about one ounce,” said Gomes. The same technology can be developed to detect other pathogens such as E. coli O157:H7, she said. But listeria was chosen as the first target pathogen because it can survive even at freezing temperatures. It is also one of the most common foodborne pathogens in the world and the third-leading cause of death from food poisoning in the U.S. Currently, the only means of detecting listeria bacteria contamination of food requires highly trained technicians and processes that take several days to complete, she said. The biosensor she is working on is still in the prototype stage of development, but in a few years she envisions a hand-held device that will require hardly any training to use. Gomes said she is using “nanobrushes” specially designed to grab particular bacteria. The nanobrushes utilize “aptamers,” which are single-stranded DNA or RNA molecules that bind to the receptors on the target organism’s cell outer membrane, Gomes said. This “binding” is often compared to the way a key fits into only one lock. In this manner, the nanobrushes select for only a specific type of cell, which in the case of her work is the listeria bacterium. Currently, the listeria biosensor is about the size of a postage stamp, with two wires leading to two etched conductive areas. After a few minutes, when the polymer nanobrushes have had time to grab the selected bacteria, the rest of the sample is washed away and the impedance, or resistance, between the two surfaces is measured electronically. In early April, the team was awarded a three-year $340,000 National Science Foundation grant to continue their work on nanobrushes for pathogen detection.