Hydrogen Peroxide Plasma Sterilization & Disinfection

Using a vacuum system to dose Hydrogen Peroxide gas and Hydrogen Peroxide plasma to medical and surgical devices has been utilized for sterilization since the late 1980s. When Hydrogen Peroxide is dosed into a plasma machine vacuum chamber the vapor diffuses throughout the chamber and contents. Due to the disinfecting properties of Hydrogen Peroxide vapor followed by plasma generated microbicidal free radicals (e.g., hydroxyl and hydroperoxyl) sterilization can be performed effectively in most materials. Following the sterilization process the chamber can be flushed then vented with filtered air to provide good industrial hygiene for an operator.

Working Principle of a Hydrogen Peroxide Gas Sterilizer

A hydrogen peroxide (H₂O₂) gas sterilizer is a device that applies H₂O₂ vapors to potentially contaminated surfaces. In principle, hydrogen peroxide can also be used in liquid form to sanitize surfaces, although it has to be diluted in that case. It is commonly applied by healthcare facilities or other institutions that have high standards of hygiene such as the manufacturers of medical devices.

H₂O₂ vapor is used to sterilize everything, from entire rooms to surgical instruments such as scalpels or endoscopes. Smaller items are usually put into a specially designed chamber and are treated with peroxide. After exposure to the vapors, the microbial load on the surfaces is greatly reduced and the fumes are evacuated from the chamber. H₂O₂ oxidizes the surface and the microbes, killing them in the process. The byproducts of these reactions are just water and oxygen, which are mostly harmless.

Another positive aspect is that hydrogen peroxide vapors can provide low-temperature sterilization (often between 40 and 100 °C, or 320 to 380 K). Due to the effectiveness in the inactivation of microorganisms, the cycle time of a sterilization chamber is relatively low. It has to be noted that H₂O₂ acts stronger on so-called gram-positive bacteria than on gram-negative bacteria (however, the latter species is usually more resilient than the former one when it comes to sterilization).

Low Temperature Sterilization with Plasma Technology

Sterilizing items or entire rooms can be easily achieved with hydrogen peroxide vapors. However, in combination with low-temperature plasma sources, this technology becomes even more potent. Plasma tends to be chemically more reactive, compared to ordinary vapors due to the ions and free electrons within it. This means that the antimicrobial properties are more pronounced. Cold plasma sources can even create H₂O₂ directly in water, which immediately yields a disinfecting liquid.

For example, a dielectric barrier discharge in water can produce up to 100 µmol of hydrogen peroxide. The H₂O₂ yield can even be higher if the feed gas contains some water vapor itself. The higher the water content in the air plasma is, the more hydrogen peroxide is created in the plasma. Those reactive molecules can diffuse into cells and cause severe DNA damage to bacteria and other microorganisms, causing them to die quickly.

Water can also be treated with air plasma. This leads to the formation of even higher peroxide concentrations in the liquid. Since hydrogen peroxide plasma has an increased chemical activity, the disinfection cycles can be much shorter compared to neutral gas H₂O₂ vapor decontamination.

Another upside is that plasma technology can also be combined with conventional hydrogen peroxide disinfection to increase its efficacy. For this purpose, a suitable plasma source is added to a sterilization chamber. The H₂O₂ vapor is introduced and a low-temperature plasma is ignited, turning the vapor into a partly ionized gas. This enhances the effectiveness of decontamination and brings down the time necessary to get rid of all unwanted microorganisms. The only byproducts of this technique are oxygen and water. Thus, there are no hazardous substances created in the process.

Conventional Sterilization Technologies vs. Peroxide Gas Plasma

Here is a list of the most prominent differences between conventional sterilization techniques, hydrogen peroxide vapor and plasma with regard to their properties:

• Hydrogen peroxide vapor sterilization cycles can take up to several hours, while H₂O₂ plasma treatment can be done sometimes in less than one hour.
• For some disinfection procedures high temperature is required. Hence, no heat-sensitive material can be treated effectively. Hydrogen peroxide plasma, on the other hand, remains comparatively cool, often below 50 °C (330 K).
• H₂O₂ has a boiling point of around 150 °C (430 K). Hence, the sterilization chamber sometimes has to be evacuated if heat-sensitive materials are to be decontaminated. This is because lower pressure brings down the boiling point and, thus, the necessary temperature. This can be avoided with hydrogen peroxide plasma because low-pressure plasma can be created even at atmospheric pressure while keeping the temperature around 50 °C (330 K).
• Unlike heat-based sterilizers that disintegrate microorganisms thermally, hydrogen peroxide directly penetrates through the cell walls and causes irreparable damage to the DNA or the microbes. This is a very reliable and fast decontamination process.
• While H₂O₂ has to be prepared from water and hydrogen peroxide, suitable plasma sources can create the same solution rapidly just from water and thin air (literally).
• Conventional sterilization systems often rely on only one mechanism to kill germs, for example, high temperature or aggressive chemicals. H₂O₂ plasma does not only work based on highly active ions but it often has synergy effects. For instance, in plasma, often strong electromagnetic fields and UV radiation can be found. These also help to get rid of resistant germs but they vanish as soon as the plasma is switched off. Therefore, no dangerous or environmentally unfriendly byproducts are created during plasma sterilization with H₂O₂.

The Advantages and Uses of Hydrogen Peroxide Plasma Sterilization

Hydrogen peroxide vapor / plasma sterilization provides a safe, non-toxic method of sterilization. It is a dry, non-thermal process that is environmentally friendly and does not produce harmful by-products associated with other methods of sterilization. Objects that are sterilized using vapor phase Hydrogen Peroxide and plasma are completely safe to handle right away because the chamber can be vacuum flushed with filtered air to remove residues left over. This process is most often used on devices or materials that can not endure high temperatures or gamma radiation associated with many sterilization techniques associated with certain plastics, electrical devices and some metal alloys. Most commonly hydrogen peroxide plasma is used to sterilize medical devices and surgical tools.