Testing food for e.coli with engineered droplets

Credit: Massachusetts Institute of Technology.

New types of liquids are being used to detect certain chemical compounds to make detection easier. These liquid droplets bind to specific protein bacteria and can display visual detection visibly or upon being scanned by a smart phone camera. This represents a much quicker way to test for specific unsafe materials and growth on food, as well as costing less than existing methods.

The innovation from MIT will bring big changes to food testing. For example, e-coli (which kills around 60 and makes around 73,000 people sick annually in America) can be detected by the new droplets. The same is true for other dangerous bacteria which can also be detected.

A professor at the university who lead the research, Timothy Swager, said the claims for the new uses of the technology are going to live up to the hype. “It’s a brand new way to do sensing, What we have here is something that can be massively cheaper, with low entry costs”, the John D. MacArthur Professor of Chemistry said.

In 2014 the lab in MIT innovated new materials that could make these compound liquids. One innovation was termed a Janus emulsion. The interesting thing about this compound is that it contains two chemicals, hydrocarbon and fluorocarbon, stuck together, but the latter is more dense. This allows the top side of the molecule to always be hydrocarbon since it is lighter when it is placed on something. So the droplet is a bottom heavy sphere 50% of each material by volume.

The droplets are see-through from a top perspective but opaque when looking at their underneath. So you get two different appearances depending on where you view them from, and this is always depending on the vertical perspective taken.

And these can then be made into sensors in an interesting way. Another molecule made from mannose sugar and coupled with the droplet bind on lectin, a common component of e.coli. So when they come in contact with e.coli the mannose based molecule attached to the lectin protein which has a knock on effect turning the droplets upside down. Then when light is applied the orientation of the molecules can be seen since they react to light differently depending on whether they are upside down or not.

According to Swager “we’re using the native molecular recognition that these pathogens use. They recognize each other with these weak carbohydrate-lectin binding schemes. We took advantage of the droplets’ multivalency to increase the binding affinity, and this is something that is very different than what other sensors are using.”

A novel and interesting demonstration of the droplets functioning was when it was applied to a Petri dish with a QR code underneath it – so that when the droplets were activated by e.coli the surface became obscured, thus preventing the reading of the code. The innovation was commented on and heralded as “a powerful new class of assays” by professor of chemistry at Northwestern University and director of the International Institute for Nanotechnology, Chad Mirkin.

He continued: “They are elegantly simple but rely on clever new approaches to making and manipulating emulsions. This proof-of-concept demonstration in detecting foodborne pathogens is compelling, as they constitute a major class of analytes that defines an unmet need in the biosensor community.” He was not involved in the research.

This innovation could be a big step forward over existing methods of detection, whereby samples are encouraged to grow and incubate any dangerous pathogens over a few days, then analysed by labs. This takes time, and a quicker approach which uses DNA analysis or another than tests using antibodies are both inaccessible and high cost.

The researchers are hoping to expand the functionality of the innovation. By adding other compounds, they can use the QR code method to detect multiple pathogens, including different strains of e.coli.

According to Zhang: “the great advantage of our device is you don’t need specialized instruments and technical training in order to do this. That can enable people from the factory, before shipping the food, to scan and test it to make sure it’s safe.”

The team are hopeful that as they continue improving the innovation that it will get more accurate and effective. It will be put on the market in the coming 18 months and will be sold by a company created for the purpose. They are optimistic that the innovation has great potential.

According to Savagatrup: “You could imagine making really selective droplets to catch different bacteria, based on the sugar we put on them.”

More information can be found at: Massachusetts Institute of Technology.

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