It’s a trap. Bacteria approach tiny microscopic spheres on a sterilized surface of a medical device. They are drawn into the hollow spheres where light is turned on them, pulling the trigger on a chemical reaction. They start to die. UNM Research Professor in Chemical and Nuclear Engineering and the Center for Biomedical Engineering David Whitten and University of Florida Professor of Chemistry Kirk Schanze have spent the last decade working on electricity-conducting polymers.
These polymers have a unique trait when they are exposed to light. They produce singlet oxygen, a reactive form of oxygen that is highly toxic to bacteria, like bleach or other potent sterilizers.
The researchers theorized they could use coatings of the polymers to sterilize surfaces, so University of Florida doctoral student Jonathan Sommer developed a method to shape them into microscopic spheres, ranging in size from one to five microns. The width of a human hair is about 10 microns.
UNM chemistry doctoral student Thomas Corbitt worked with colleagues at UNM to test the spheres, using a safe laboratory strain of Pseudomonas aeruginosa, a common, persistent and lethal bacteria in hospitals. That bacterium is often introduced via contaminated medical devices and can sicken or kill patients suffering from burns, cancer, AIDS and other serious conditions. He tested the effectiveness of the light induced chemical reaction in killing the bacteria. Corbitt says, “It was very exciting to see the microspheres immobilizing and killing the bacteria so quickly.”
Whitten explained, “We expected that these hollow capsules might behave on the micro scale with bacteria much like the insect trapping Roach Motels™. We had done some work with Pseudomonas aeruginosa strain PAO1 with one of the two polymers used in constructing the capsules and found some activity against it.
"We also realized that it was difficult to kill Pseudomonas compared to other bacteria we were working with. Our finding that the ‘micro roach motels’ are far more efficient at both entrapping the bacteria and then killing them with light was a wonderful result, even taking into account that we specifically designed the capsules for this purpose.”
Microbiologist Linnea Ista, a research scientist at the Center for Biomedical Engineering, worked directly with Corbitt in the test phase. “There is something fascinating going on at the interfaces between these surfaces and bacteria,” she said. “In addition to the potential for being useful biocides, these are intriguing surfaces because they trap so many bacteria so quickly.”
Center research assistant Sireesha Chemburu noted, “The need for self sterilizing materials has gained immense importance due to its major contribution in decreasing hospital related infections. The driving force behind this research work is the direct contribution and the impact on the society. The ultimate success of this research work will be realized when we no longer have to think twice about touching a hospital door knob or whether a surgical instrument has been sterilized properly.”
A paper outlining the results will be published this week in the debut issue of American Chemical Society Journal “Applied Materials & Interfaces.” Collaborating on the paper are Thomas S. Corbitt, Sireesha Chemburu, Linnea K. Ista, Gabriel P. Lopez and David G. Whitten from UNM and Jonathan R. Sommer, Katsu Ogawa and Kirk S. Schranze from the University of Florida.
The paper is available at: Roach Motel™.
Schanze and Whitten say further tests are needed to nail down the potency of the spheres, but initial experiments indicate they wiped out more than 95 percent of nearby PAO1 bacteria after exposure to light for about an hour.
They point out the spheres are far from the only “biocide” on the market or under development, but they are unique in the materials used and the method of trapping the bacteria. That might be important as the bacteria evolve to become more and more resistant to standard disinfectants.
Funding for the research came from the Defense Threat Reduction Agency, and the spheres might be used in filters to trap bioterrorism agents. Schranze and Whitten say the materials used for the spheres are not exotic or expensive, and may have potential to be produced at industrial scale. UNM and UF filed a joint patent application for the spheres.
Media Contact: Karen Wentworth, (505) 277-5627; e-mail: kwent2@unm.edu