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Light-Activated Nanoparticles Help Fight Drug-Resistant Superbugs

Quantum dots boost the efficacy of antibiotics

3 min read
light-activated nanoparticles shown glowing on lab tray
Image: Mason Marino/University of Colorado Boulder

Our strongest antibiotics are increasingly defenseless against the nastiest bacterial infections, but the use of new light-activated nanoparticles could give those old drugs a fighting chance. In a paper published today in Science Advances, researchers reported that quantum dots—light-activated semiconductor nanoparticles—when engineered at a particular size can sneak into bacteria, disrupt their cellular processes, and make them more susceptible to antibiotics.

The discovery could breathe new life into old antibiotics, says Anushree Chatterjee, a chemical and biological engineer at the University of Colorado Boulder, who co-authored the report. It also exemplifies how electrical engineering can be used to address problems typically approached purely though medicine.

Antibiotics—the infection-killing wonder drugs that revolutionized 20th-century medicine—have been outmaneuvered by their enemy. The toughest bacterial strains, or superbugs, can weather up to 20 different antibiotics—nearly every tool in a doctor’s toolbox. “They come up with new enzymes and new countermeasures to defeat anything we throw at them,” says Prashant Nagpal, a chemical and biological engineer at UC Boulder who co-authored the report.

The drug-resistance problem is especially bad in hospitals and on farms—hotbeds for superbugs, Nagpal says. Yet drug companies have largely failed to put new, more effective antibiotics on the market due to small profit margins.

Quantum dots have been used in engineering to achieve many technical feats, but using them to re-invigorate antibiotics is a first, Nagpal says. The dots achieve the effect by lowering bacteria’s defenses, making them more vulnerable to attack from antibiotics. It’s like hitting them while they’re down: A “one-two punch,” says Nagpal.

The dots are made of cadmium telluride, a semiconductor material that is sensitive to light. The key was to engineer them at precisely three nanometers in diameter. At this size, when exposed to visible light, electrons on the surface of the dots become excited and are transferred to oxygen molecules in the surrounding water. The oxygen molecules, with the addition of an electron, become superoxides—free radicals that mess with bacteria’s metabolism and cellular processes.

While superbugs are busy dealing with superoxides, antibiotics can slip in for the kill. “The bacteria has to activate stress-response pathways,” when exposed to high levels of superoxides, says Chatterjee. “So it changes its metabolism to counter that kind of stress, and when it does, that makes it more vulnerable to the antibiotic,” she says.

diagram of superbugQuantum dots inside an antibiotic-resistant “superbug” stress the bacteria and make it more vulnerable to antibiotics.Illustration: University of Colorado Boulder

The levels of superoxide produced are just enough to affect bacteria but not human cells, Nagpal says. “Our cells can handle ten times more, so they are fine. It’s routine for them,” he says.

Nagpal and Chatterjee tested the system on E. Coli, Salmonella and another drug-resistant bacterium called Klebsiella pneumoniae. They hit them first with the quantum dots and then with an antibiotic, and found that the dot system killed the bacteria up to a thousand times better than the antibiotic alone.

The inventors say they envision introducing the quantum dots to patients by having them breathe them in, or by injection into the bloodstream. Then the patient would simply “take a stroll outside” and let the sun activate the dots, Nagpal says. Patients could also sit in a well-lit room or wear clothes lined with visible LEDs, he says.

Such light would penetrate and activate quantum dots up to a tenth of a centimeter into the body. To reach infections deeper in the body, Chatterjee and Nagpal are developing materials that respond to near-infrared light. They hope to further develop the materials and conduct animal testing so that they can move the technologies into clinical testing.

Even if they succeed, researchers will likely need to be ready with another tool to follow it. Bacteria are masters at evolving resistance, and will likely find a way to withstand superoxides too. Says Nagpal: “I’m sure they’ll fight back.”

The Conversation (0)
Illustration showing an astronaut performing mechanical repairs to a satellite uses two extra mechanical arms that project from a backpack.

Extra limbs, controlled by wearable electrode patches that read and interpret neural signals from the user, could have innumerable uses, such as assisting on spacewalk missions to repair satellites.

Chris Philpot

What could you do with an extra limb? Consider a surgeon performing a delicate operation, one that needs her expertise and steady hands—all three of them. As her two biological hands manipulate surgical instruments, a third robotic limb that’s attached to her torso plays a supporting role. Or picture a construction worker who is thankful for his extra robotic hand as it braces the heavy beam he’s fastening into place with his other two hands. Imagine wearing an exoskeleton that would let you handle multiple objects simultaneously, like Spiderman’s Dr. Octopus. Or contemplate the out-there music a composer could write for a pianist who has 12 fingers to spread across the keyboard.

Such scenarios may seem like science fiction, but recent progress in robotics and neuroscience makes extra robotic limbs conceivable with today’s technology. Our research groups at Imperial College London and the University of Freiburg, in Germany, together with partners in the European project NIMA, are now working to figure out whether such augmentation can be realized in practice to extend human abilities. The main questions we’re tackling involve both neuroscience and neurotechnology: Is the human brain capable of controlling additional body parts as effectively as it controls biological parts? And if so, what neural signals can be used for this control?

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