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Biosensors to provide rapid detection of Salmonella

Each year, 40,000 cases of salmonella are reported in the United States, though the Centers for Disease Control (CDC) believes that contaminated food may cause up to 35 times that many. It is the second leading cause of food-related illness of bacterial origin. Annually, more than 400 deaths are attributed to the bacterial pathogen, with the highest risk occurring among children, the elderly and those with compromised immune systems.

Though the Food and Drug Administration requires that samples of potentially at-risk foodstuffs be tested, results from prevailing procedures may take up to a week to complete. Various bacteria detection biosensors, including micro-electrical mechanical systems (MEMS), have reduced detection time to just a few days or even hours, however, a novel device conceptualized by Mahmoud Almasri, assistant professor in electrical and computer engineering at the University of Missouri, holds promise for testing with rapid results. The National Science Foundation is supporting his research of the proposed biosensor with a grant of $306,000. Majed Dweik, assistant professor in the department of agriculture, biology, chemistry and physics at Lincoln University in Jefferson City, is collaborating on the project.

“Usually testing is done in two dimensions with electrodes lying down on a substrate,” said Almasri, describing the predominant design of interdigitated microelectrode array (IDE) devices currently used for pathogen detection, explaining that this type of detection lacks finesse.

“With the MEMS device we are working on, the sensing surface area to volume ratio is significantly increased,” Almasri said, explaining the advantage of his design.

The biosensor Almasri’s research group is developing will have multi-channels and multi-three-dimensional interdigitated electrode arrays, one of which is coated with antibodies that will bind with salmonella antigen.

“3-D capabilities increase the sensitivity of detection, and the ability to concentrate and confine a few cells into a smaller volume,” said Almasri. This will allow for fast and accurate detection.”

“The concept of utilizing antibody and antigen binding has been used in optical sensing and other types of sensing for many years,” said Dweik, referring to components of the research project for which he is responsible. “The challenge in detection of pathogens is identifying small concentrations.”

“When we flow the Salmonella contaminated fluid into the microchannel, the bacteria will be attracted to the antibodies,” Almasri said, explaining that binding between the bacteria and the antibodies will cause a change in the impedance – a measurable electrical signal – which will be correlated to the concentration of bacteria in the sample.

In addition to being efficient and accurate, the device will be much smaller, lighter and less expensive than current array units, with its portability contributing to its integration into field-testing.

Salmonella detection is the primary focus of the three-year research project, and biosensor testing is planned utilizing samples of peanut butter, cantaloupe, mangoes and tomatoes. The pair of researchers believes that the process can be easily altered to detect a variety of pathogens that pose human health risks such as Escherichia coli and listeria. Beyond using the technology in the food and packing industry, it also could potentially have bioterrorism applications such as the detection of pathogens in water.