PLASMA STERILIZATION  

      

  Plasma sterilization is fast evolving into a promising alternative to standard sterilizing techniques. Research on plasma sterilization started way back in 1960. Since then, extensive research has been performed in plasma sterilization. There are numerous parameters involved such as the pressure or the type of gas used etc. In an effort to arrive at the optimal mix of parameters, numerous experiments have been performed. What is available? • Disinfectants- These are basically used to “kill bacteria to an acceptable

level”. They cannot completely eliminate micro-organisms. • Autoclaving- Autoclaving uses very high temperatures to effectively kill any

pathogens. • EtOH- Ethylene oxide treatment is generally carried out between 30 °C and

60 °C with relative humidity above 30% and a gas concentration between 200 and 800 mg/L for at least three hours. The process also involves a period of post-sterilization to remove any toxic residues

• There exist other techniques such as Gamma irradiation and the like but are quite impractical for everyday use.

Why Plasma sterilization? • The process is usually at room temperature and hence poses no dangers

associated with high temperatures (unlike autoclaves) • Doesn’t involve any chemicals and hence is non-toxic (unlike EtOH) • Time of treatment is fast and of the order of 1 min or less.

Before Sterilization After Plasma Treatment

• Is versatile and can sterilize almost any material and any shape with nooks and crannies

How does it work? Without going into the nitty gritties, simply put, plasma sterilization uses a tri-phasic technique. Plasma is basically ionized gas. When you apply an electric field to a gas, it gets ionized into electrons and ions and Voila! The plasma we generate in our lab is named Dielectric Barrier Discharge. Look at the picture at the top of the page. Now imagine a layer of spores on a surface as shown at the top of the page. When the plasma is turned on, it generates a whole lot of particles- UV photons, electrons, ions and neutral particles. The electrons and ions just swim around. It’s the UV photons and radicals that do all the hard work. Most of the research in plasma sterilization pertains to volume discharge. Tri-phasic behaviour was observed in these experiments. The process involves UV irradiation, photo-desorption and chemical etching. The spores are basically made up of simple atoms like C, O, N, H and the like. The radicals react with these atoms to form simple compounds like CO2, which can subsequently be flushed out. When the organism loses such atoms that are intrinsic to its survival, it dies. A few points to be noted: • We have performed tests wherein we have exposed a solution of yeast

spores to plasma for different times of exposure. • As can be seen above, after 24 hours of incubation, almost all the spores on

the yeast layered plate are killed. While results like these require definite validation by way of microscopic examination and other standard tests, they are definitely encouraging!

• Future work involves carrying out tests for different electrode patterns and examining the effect of plasma sterilization on complexly shaped objects.