"Superbugs" Destroyed Using Quantum Dot Nanoparticles

Superbugs versus Quantum dots. Who'll triumph now that antibiotics are becoming increasingly ineffective? anyaivanova/Shutterstock

Back in 2014, the World Health Organization issued a report declaring that antimicrobial resistance (AMR) had become a global health security threat. Various “superbugs” are evolving too rapidly to be counteracted by traditional drugs. A new study published in Nature Materials could offer some hope, showing that tiny structures called nanoparticles can be turned into targeted, destructive weapons that can destroy resistant bacteria by using nothing more than light.

AMR occurs when microbes evolve defensive mechanisms designed to evade therapeutic agents, thus rendering these drugs partly or completely ineffective as forms of treatment. Largely due to the oversubscription of antibiotics to people and their overuse within intensive livestock farming, the situation has led many to suspect that we are entering a post-antibiotic era. Not only does this make once-treatable infections far more difficult to treat, it also means that they could potentially become life threatening. Fortunately, a team at the University of Colorado Boulder has engineered a weapon for us to use against our bacterial foes.

Quantum dots (QDs) are essentially small crystals of nanometer-size dimensions – they’re about 20,000 times smaller than the width of a human hair. They have distinctive electrical conduction properties that are determined by the incredibly small size and structure.

Nano-sized cadmium sulfide quantum dots – one of many types. U.S. Department of Energy.

When these QDs are hit with a specific frequency of radiation, their changeable structure, tailored by scientists, means that they can be finely tuned to emit a specific frequency of radiation; changing the wavelength of the light source can achieve the same effect. In this study, the researchers decided to try and use customized QDs against antibiotic-resistant bacteria, including E. coli and Staphylococcus aureus, in a laboratory setting. In the dark, the QDs remain inactive. When bombarded by visible light, they become energetically “excited.”

When placed among bacteria in a solution, something interesting happens. Bacteria rely on “redox” reactions, those involving the addition or removal of oxygen (reduction and oxidation, respectively). And when several QDs are “excited” nearby, they produce chemicals that are able to be reduced or oxidized by reactive compounds within the bacteria. This effectively interferes with their intercellular processes, disrupts their cell growth, and kills them. In a lab-grown culture, this method has been shown to kill 92 percent of a variety of drug-resistant bacterial cells, while leaving other cells alone.

Previously, tiny graphene nanoparticles have been shown to effectively transport anti-cancer drugs inside them during novel chemotherapy treatment, and some can even be triggered to heat up to annihilate cancerous tissue. In a similar way, QDs – roughly the same size – could be injected into the human bloodstream, and designed to target specific infections by being stimulated with various wavelengths of light.

“While we can always count on these superbugs to adapt and fight the therapy, we can quickly tailor these quantum dots to come up with a new therapy and, therefore, fight back faster in this evolutionary race,” said Prashant Nagpal, an assistant professor in the Department of Chemical and Biological Engineering at CU-Boulder and a senior author of the study, in a statement.

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