The small sensor, seen under a magnifying glass is an array of microcantilevers, could make it faster and easier for food-manufacturing plants to detect pathogens. (Credit: Jeff Fitlow/Rice University)

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This tiny sensor spots salmonella in minutes, not days

A new biosensor quickly detects salmonella in food and can be easily customized to detect other types of bacteria—or even different strains for the same bacterium.

The process appears to easily outperform tests that are now standard in the food industry, according to researchers at Rice University. Those tests are slow because it can take days to culture colonies of salmonella bacteria as proof, or laborious because of the need to prepare samples for DNA-based testing.

Different strains of salmonella are captured by microcantilevers decorated with peptides that have unique binding affinities to different strains of the pathogen. When a peptide catches a bacterium, the cantilever bends ever so slightly, due to a mismatch in surface stress on the top and bottom. A fine laser trained on the mechanism catches that motion and triggers the alarm. (Credit: Jinghui Wang/Rice University)
Different strains of salmonella are captured by microcantilevers decorated with peptides that have unique binding affinities to different strains of the pathogen. When a peptide catches a bacterium, the cantilever bends ever so slightly, due to a mismatch in surface stress on the top and bottom. A fine laser trained on the mechanism catches that motion and triggers the alarm. The sensor was developed at Rice University. The technique could greatly simplify the food industry’s tests for pathogens. (Credit: Jinghui Wang/Rice University)

The device, which can be cleaned and resued, has a set of microcantilevers—like tiny diving boards—each of which can be decorated with different peptides that have unique binding affinities to strains of the salmonella bacteria.

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When a peptide catches a bacterium, the cantilever bends ever so slightly, due to a mismatch in surface stress on the top and bottom. A fine laser trained on the mechanism catches that motion and triggers the alarm.

The system is sensitive enough to warn of the presence of a single pathogen, according to the researchers, who say that very low pathogen concentrations cause foodborne disease. They describe the technology in a study published in the journal Analytical Chemistry.

Peptide targets

Researchers at Rice collaborated with Nitsara Karoonuthaisiri, head of the microarray laboratory at the National Center for Genetic Engineering and Biotechnology, who had isolated bacteriophage viruses associated with salmonella through biopanning and phage display, a technique to study interactions among proteins, peptides, and pathogens. She then derived peptides from the phages that would serve as targets for specific bacteria.

“She said, ‘We spend a lot of time trying to characterize which of these peptides work the best. It looks like you have a platform that can do and quantitate that.’ So that’s where we came in,” says Rice biomolecular engineer Sibani Lisa Biswal.

The Rice lab compared the peptides’ performance with commercial antibodies now used for salmonella detection and found the peptides were not only more sensitive but could be used in a multiplexed cantilever array to detect many different kinds of salmonella at once.

“The peptides are very robust,” Biswal says. “That’s why a lot of people like them over antibodies. The peptides can handle harsher conditions and are much more stable. Antibodies are large proteins and break down more readily.

“We’re very excited to see where this will lead,” she adds.

Researchers from the Institute for Global Food Security at the Queen’s University, Belfast, collaborated on the project, which received funding support from the Welch Foundation, a Hamill Innovations Award Grant, the European Union’s Seventh Framework Program, and a Marie Curie Fellowship.

Source: Rice University

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