Gloves Armed With Glowing Bacteria May One Day Detect Toxins or Disease
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E. coli have a bad rap. The very name conjures up mental images — and sounds and smells — of diarrhea and vomiting, but that species of bacterium is actually a kind of golden goose. Even as you’re reading these words, they are teeming in your gut, producing helpful vitamins; in labs around the world, they are filling Petri dishes with offspring, allowing for all kinds of experiments. And at the Massachusetts Institute of Technology, a team of scientists engineered them so that they would turn bright green when they came into contact with certain chemicals.
That sounds really useful, but there is a catch: It was all happening in liquid-filled lab dishes, which hampered many of the real-world applications.
“In a Petri dish, you can keep the humidity very high,” said Xinyue Liu, a PhD student in mechanical engineering at MIT. “When the cells are exposed to the air, they will quickly lose their water and die."
Liu and her lab-mates have been able to get around that, as they reported in the Proceedings of the National Academy of Sciences in February: They managed to keep the bacteria alive in gloves and bandages, parts of which glow when they detect certain chemicals. The technology is not yet perfect, but Liu’s hope is that it could at some point be used to pick up dangerous toxins or the chemical signs of disease.
These living materials posed a challenge: Liu needed to create a home for cells, replete with water and nutrients, into which chemicals could leech, but out of which the bacteria couldn’t escape.
What she did was to use an amalgam of a hydrogel and a rubber-like material.
Hydrogels can be a bit like synthetic human tissue, with chains of molecules that are able to contain large amounts of water — a good bet if you want to prevent something from dehydrating. But hydrogels themselves can lose their water if left out for too long.
The lab had already found the solution to that problem: attach it to what is basically rubber. Liu molded the rubber so it had tiny channels in which the bacteria could reside — the way one might build a backyard shed for a dog — and on top of that, she added a layer of hydrogel. To attach the two, she coated the rubber with a chemical, and then put the whole thing into what looks like it could be a Soviet microwave. Rubber and hydrogels don’t usually stick, and the ultraviolet light produced inside that silver box bonds those two very different materials together.
Then, she injected the cells, suspended in liquid, into those molded channels, and sealed up the needle-hole, trapping the cells inside. “It cannot escape from the hydrogel, because it’s too big too diffuse out,” explained Hyunwoo Yuk, another PhD student in the same lab, and another author of the paper.
The bacteria can’t get out through the hydrogel — “It’s a very disturbing concept for ordinary people, touching those genetically engineered E. coli onto their skin,” said Yuk — but the material provides the cells with water, and lets tiny chemical molecules leech through.
When Liu tried out these cell-filled gloves and bandages, exposing them to common lab chemicals, they didn’t light up immediately. But after a few hours they began to turn an eerie green.
“The mechanical properties of these systems are really amazing,” Eric Andrew Appel, an assistant professor of material science and engineering at Stanford, wrote in an email to STAT. He added, though, that more work needs to be done so that these living sensors can last longer.
The paper’s authors are now working on speeding the process up, so that it doesn’t take three or four hours to light up when it senses a chemical. They also have yet to try it with any of the molecules that the finished product would hopefully detect, such as environmental toxins or biomarkers of disease.
If they manage that, though, the tables would once again be turned: These E. Coli, instead of getting you sick, might hone in on a diagnosis by emitting an otherworldly glow.