Results have recently been released concerning research on low temperature oxygen plasma sterilization with samples of Pseudomonas aeruginosa as the target.   These were placed on polyethylene terephthalate (PET) sheets inside a self designed reactor.  The study was conducted by Yang L, Chen J, Gao J, Zhang Z, and Hu M, at the School of Life Science and Technology, Xi’an Jiaotong University, in Xi’an China.  They exposed this human opportunistic pathogen to a stream of ionized gas for 30 seconds.  In depth observation of the samples within the discharge area, afterglow area, and the remote area confirmed efficacy of sterilization.

Although the article reporting the results was written in Chinese and had a somewhat difficult translation, the English version was fairly clear in its conclusion: “The active species can be separated effectively in this reaction equipment, and we further elucidated the mechanisms of plasma sterilization in the remote plasma field.”  Basically that means the target species was destroyed and we know how the process worked.  Bacterial cell walls literally cracked open, and the pathogens could not survive.

The Chinese have been researching novel ways to accomplish sterilization over the last decade or so.  China is dealing with many problems involving air pollution and environmental contamination.  As the nation continues to develop, scientists are actively seeking to solve these problems (something that is not often mentioned in headline news). Any new tools that can help will certainly be put to good use.

This oxygen plasma method has been used as part of a system for air purification in the past.  Isolating what actually happens in this process could potentially lead to broader and more efficient sterilization options.  Such innovations would be welcome in the food packing industry and for medical applications.  This type of sterilization is currently thought to be completely harmless to any humans who may be in the vicinity of active equipment.

Photocatalytic Oxidation

One approach used to sparingly clean the air in the past has been photocatalytic oxidation.  It was a process originally developed by the Sandia National Laboratories in the U.S. decades ago during the “Cold War”.   The idea is to create oxygen plasma quickly and effectively by using UV-C light projected upon a substrate of titanium dioxide in a chamber.  The UV-C light has germicidal effects on its own, but the electromagnetic reaction with the specific metallic oxide creates the plasma and additional synergistic sterilization.  The TiO2 literally glows and amplifies the germicidal effect.  It also neutralizes any volatile organic compounds in the air.  Such VOCs can easily contaminate certain industrial and work environments, so eliminating them is essential.

The curious thing about this technique is that little was known in the past about how it actually worked so effectively.  More research over the last few years has isolated the plasma creation process. There are claims that other materials besides TiO2 can now be used to generate the oxidation reaction in the air.  The key to success is length of the exposure time.

The reason this technology has been limited in the past is because laying down a photo active surface of titanium dioxide in such a way that it will not restrict air flow is difficult.  Elaborate coatings must be created so that the TiO2 is both high performance and durable.

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