The normal sterilization process is automated and consists of 5 steps:
1. Precondition: Raising of humidity to make spores susceptible to gas
2. Condition: Holding of raised humidity level for spore softening
3. Charge: Injection of gas into chamber
4. Exposure: Holding of gas concentration for the set amount of time
5. Aeration: Expulsion of gas and humidity
Some microscope manufacturers add a sixth step which is a pre-purge of the system with nitrogen. If a Pre-Purge step is used, the valves are opened and nitrogen is passed through the system.
In 2009, ClorDiSys was approached by JEOL USA as they set forth to find a suitable decontamination method for their electron microscopes. They wanted a method to decontaminate the interior chambers to protect their service workers from the pathogens being studied within. Identical sets of parts were sent for material testing against chlorine dioxide and hydrogen peroxide vapor. According to “Construction and Organization of a BSL-3 Cryo-Electron Microscopy Laboratory at UTMB” in the December 2012 Journal of Structural Biology, their early attempts to use VHP with JEOL microscopes were not successful because of unacceptable level of corrosion of some parts inside the microscope column. Some showed visible discoloration and corrosion after the level of exposure necessary for a single decontamination cycle. Chlorine dioxide gas has a lower oxidation potential than ozone, peracetic acid, bleach and hydrogen peroxide, making it scientifically less corrosive than those other decontaminating agents. Our chlorine dioxide gas was selected due to its success in the material compatibility trials and is used with the $3 million TEM.
Read more about the process and benefits of using chlorine dioxide for Electron Microscope decontamination in our application note.