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Canadian researchers develop strip to show if food is spoiled by Karen Graham, July 8, 2018

A strip of plastic film may one day make "best before" dates irrelevant. Thanks to research being conducted at Canada's McMaster University, the food packaging itself may soon definitively tell you if the food is safe to eat.

When there is an outbreak of a food-borne infection, consumers are always reminded to return a product to the store where it was purchased or throw it out because quite often, it is impossible to tell if a product is unsafe to eat just by smelling or looking at it.

A team of researchers at McMaster University in Hamilton, Ontario are hoping to make it easier for consumers to tell if a package or meat or salad greens is contaminated with a potential pathogen, like E. coli, by simply looking at a small, thin, plastic patch they call Sentinel Wrap, reports CBC Canada.

One side of the transparent, durable, and flexible sensing strip is coated with a microarray of droplets of DNA molecules known as DNAzymes. If a pathogen, like E. coli, comes in contact with the DNAzymes, the strip will light up.

Consumers will be able to use an app on a Smartphone or other mobile device to "read" the fluorescence to see if the food inside the wrap was spoiled. And while the strip looks simple enough, it has taken 15 years of research and development to get it to work, says Tohid Didar, an assistant professor in McMaster's chemical and mechanical engineering department.

"A DNAzyme is a piece of DNA where the sequence has been selected such that it performs a specific activity – in this case, it's a cleavage event – in the presence of a specific target," McMaster's Prof. Carlos Filipe explained to us. "Essentially the sequence has been designed so if a bacteria is present, that DNA is going to be broken in a particular location."

Prof. Filipe explains the process, reports NewAtlas: "If you can imagine that the DNAzyme is like a rope, and there are scissors that are going to cut that rope in a specific place, those scissors are the presence of E. coli."

"On one side of the rope, you have a fluorescence molecule, on the other side, you have a quencher. If the rope is intact, they cancel each other out. But if you cut it with the scissors, and the two pieces become separate, now the fluorescence can be detected because the quencher is no longer attached."

Making use of an inkjet printer

The patch is about the size of two postage stamps. The scientists believe mass production of the patch should be relatively easy and cheap. Basically, the DNAzymes are deposit as tiny droplets on a polymer using an inkjet printer.

The team is also developing Sentinel Wrap patches for other types of food-borne bacteria, including salmonella and listeria. The patches also work for detecting contamination in water and other liquids.

What is very exciting is the other possible uses for the technology. It could be applied to bandages that indicate if wounds are infected, or put into the packaging of sterile surgical instruments to indicate if they are indeed, sterile.

And with the current methods for detecting E. coli taking almost a full day, Didar says: "You need to take the package, open it, process it, take it to a lab, either culture that sample or try to do different laboratory-based experiments to find out what's going on. Our goal is to avoid all that so you can get real-time information."

This research was published in April in the journal ACS Nano. It was also published in the US National Library of Medicine National Institutes of Health NCBI Journal in April.