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Tiny magnetic bots that are activated by light can clear bacterial infections deep in the sinus cavities, then be expelled by blowing out the nose.

A new study in Science Robotics unveiled copper single–atom–doped bismuth oxoiodide microbots, each smaller than a grain of salt, that can be tracked and guided to the location of infection via X-ray imaging, thus providing a precise, minimally invasive therapeutic strategy for managing sinusitis clinically.

Sinusitis is a common respiratory condition often linked to biofilm produced by bacteria like Streptococcus pyogenes. This condition causes inflammation of the sinus lining and leads to symptoms such as nasal congestion, reduced sense of smell, facial pain, and, in some dire cases, even memory impairment.

Complex microbial communities, such as those involved in sinusitis, often form biofilms—structured assemblies where multiple microorganisms adhere to a surface and secrete polymeric substances. These secretions create a three-dimensional scaffold that shields the microbial colony against external threats, such as antibiotics and physical disruptions.

Furthermore, inflammatory responses triggered by bacterial infections in deep sinus cavities can lead to the formation of pus, which is highly viscous and can act as a biological barrier, preventing conventional treatments from reaching the infected site.

These obstacles make it extremely difficult to treat sinus infections, a region that is already hard to reach due to its narrow openings.

Around 8–13% of the global population have to deal with chronic sinusitis, and invasive surgical procedures shouldn't be the only way to treat this issue.

The researchers introduced a minimally invasive approach to treating the infection using their novel photocatalytic microrobots, comprising copper single–atom–doped bismuth oxoiodide in a hemispherical core-shell structure with a diameter of approximately 3 μm. They precisely delivered these microbots into the sinus cavities of rabbits in pre-clinical trials through a magnetically guided optical fiber.

The injected microbot swarm was then continuously irradiated with visible light, initiating a photothermal effect that significantly reduced the viscosity of the pus. Once floating in a more liquefied pus, the CBMR swarm was three times more effective at reaching and treating the infected site.

Upon reaching the infection site, the bots produced large amounts of reactive oxygen species (ROS), made possible by the synergistic effect of copper single atoms and bismuth oxoiodide (BiOI) photocatalysis.

These highly reactive ROS molecules not only broke down the biofilm but also killed the infection-causing bacteria. In the rabbit sinusitis model, this treatment strategy effectively cleared the infection without causing significant tissue damage or side effects.

A minimally invasive method that offers relief to millions with recurrent sinus infections also opens the possibility of this approach being adapted for other deep-seated or mucus-protected infections, such as those in the lungs or digestive tract.

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