UCSD Jacobs School of Engineering University of California San Diego
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Cold Plasma Kills Bacteria

Researchers at the Jacobs School and Old Dominion University successfully tested a new way of killing bacteria with ‘cold plasma’, which is produced at room temperature and pressure. The work could have applications in sterilizing medical instruments without use of toxic chemicals, and in sterilizing food packaging.

The results are published in the April 30 issue of the New Journal of Physics. D. Asoka Mendis, professor emeritus of electrical and computer engineering (ECE) at the Jacobs School, and ECE researcher Marlene Rosenburg, both experts in complex plasmas, provided theoretical consultation on experiments conducted by Mounir Laroussi at Old Dominion.

Plasma is an ionized gas comprised of electrically charged particles (e.g. electrons) and non-charged particles (e.g. radicals) which is typically created by superheating gas. A successful way to make cold plasma at room temperature was developed in the 1990s. A solution of 97 percent helium and three percent oxygen is injected into a gap between two flat electrodes, and then the electrodes are supplied with between 50 and 300 watts of power (less than many food processors require).

The researchers tested the effects of this plasma on two types of bacteria – Bacillus subtilis and Escherichia coli. The former is a resilient, hard to kill, spore-forming type, similar to anthrax. The latter does not have spores and is one of the common causes of food poisoning.

After being exposed to the plasma, both types of bacteria were successfully destroyed. The ultra violet radiation and radicals in the plasma damaged many parts of the bacteria, including the DNA. In addition, the charged particles within the plasma tore the outer cell membranes of the non-spore-forming bacteria.

Mendis says the charged particles in cold plasma could likely kill other kinds of more dangerous bacteria as well as viruses, and the team will continue experimental work in that

E. coli before plasma treatment
Process could be used to sterilize medical instruments without use of toxic chemicals
Damaged E.coli following treatment