Patch designed to detect pathogens in packaged food

TORONTO — Researchers at McMaster University have developed a transparent test patch for food packaging that detects the presence of potentially deadly bacteria such as E. coli, with the aim of telling consumers and the grocery industry whether a product is safe to eat.

Dubbed “Sentinel Wrap,” the patch triggers a molecular signal that a disease-causing agent has contaminated products such as meat, bottled water or milk.

“Right now, if you want to know if there’s any contamination in a food sample, you need to bring it into a lab and it takes at least a day or two to find out if there’s any pathogen present in that food sample,” said mechanical-biomedical engineer Tohid Didar, one of the product’s developers.

“Our goal was to be able to find this at the site, either at home when you want to start using it or on the shelf when you’re buying it or for the supermarket manager who is handling this or even the person who transports it,” he said.

The patch is dotted with tiny drops containing DNA molecules, created on an ink-jet printer, that target a specific bacteria — in this case Escherichia coli, which can cause severe illness and even death. In May 2000, a virulent strain of the pathogen sickened 2,500 people and killed seven in Walkerton, Ont., after the town’s water supply became contaminated.

E. coli mostly lives in the intestines of cattle, but the bacteria have also been found in chickens, deer, sheep and pigs. The animals’ feces containing the bug can find its way into groundwater.

Didar said the patch could be incorporated into food packaging material, so that it comes into contact with the product. If a pathogen is present, the drops would “light up” — a response that could be read by a smart phone camera with a specialized filter or a simple hand-held device that picks up fluorescence.

“So as soon as the bacteria is present, the bacteria itself or what the bacteria secretes triggers these sensors and they start shining up,” said Didar. “And just the same way you can scan a bar code, you can scan a sample and see if there’s E. coli present in the food sample or not.”

The test patch does not affect the contents of the package.

Graduate student Hanie Yousefi, lead author of the study, said the device has the potential to replace the traditional “bestbefore” date on food and drinks by showing if a pot roast, for instance, should be ditched or a carton of milk poured down the drain. “In the future, if you go to a store and you want to be sure the meat you’re buying is safe at any point before you use it, you’ll have a much more reliable way than the expiration date,” she said.

So far, the new technology has been developed to detect only E. coli. In a proof-of-concept study, published Friday in the journal ACS Nano, the research team tested the patch in meat, chicken, water, milk, sliced apple and apple juice exposed to the bacteria. Those tests showed the device detected the targeted bug, but did not create false-positive results when it came in contact with harmless bacteria present in the foods and beverages.

Statistics from the World Health Organization show foodborne pathogens represent a major threat worldwide, causing about 600 million illnesses and 420,000 deaths each year.