Radiation Method of Sterilization

This type of method is carried out for surface sterilizations. Many types of radiation are used for sterilization like electromagnetic radiation (examples: UV rays and Gamma rays). There are two types of radiation used for sterilization, ionizing radiation and non-ionizing radiation. Ionizing radiation is the use of short-wavelength, high-intensity radiation to destroy microorganisms. This radiation comes in the form of gamma or X-rays that react with DNA resulting in a damaged cell. Non-ionizing radiation uses longer wavelengths and lower energy, and is only used for sterilizing surfaces. The most common form of non-ionizing radiation is ultraviolet light. Gamma radiation is very penetrating and is commonly used for the sterilization of medical equipments like syringes, needles, etc. It is generated by cobalt 60. X-ray is the form of ionized energy allowing to irradiation of large packages for the sterilization of medical equipments. E-beam radiation converts X-ray for more penetration but sometimes E-beam radiation is not applied for complex products. Infrared radiation is considered a form of hot air sterilization. It is used for rapid mass sterilization of pre-packed items like syringes, catheters, etc.

Flowchart: Radiation sterilization

Principle of Ionized Radiation: It causes death or mutations in microorganisms as they damage the DNA and protein.

Principle of Non-ionized Radiation: Cellular DNA absorbs the energy by purine and pyrimidine bases when microorganisms come in contact with UV light. During that time linked thymine molecules are unable to encode adenine on messenger RNA molecules during protein synthesis and finally no longer produce protein. UV light also inactivates viruses. UV wavelength in the 200 nm to 265 nm range is most effective in killing microorganisms.

Advantages of Radiation Sterilization:

• It effectively reduces the number of airborne microorganisms and kills them.

• No degradation of media during sterilization, thus it can be used for thermally labile media.

• It leaves no chemical residue.

• Its administration of precise dosage and uniform dosage distribution.

• Its immediate availability of the media after sterilization.

Disadvantages of Radiation Sterilization:

• This method is a more costly alternative to heat sterilization.

• This method requires highly specialized equipment.

Applications of Radiation Sterilization:

• UV light is the most lethal component in ordinary sunlight used in the sanitation of clothes and utensils.

• Gamma rays are used to sterilize antibiotics, hormones, sutures, plastics, etc.

The table below depicts the advantages and disadvantages of overall methods with their mechanisms.

Methods	Mechanism	Advantages	Disadvantages	Applications
Physical: Heat sterilization	Destroys bacterial endotoxins by denaturation of proteins and oxidative damage.	The most widely used and reliable method of sterilization involves the destruction of enzymes and other essential cell constituents.	Can be applied only to thermostable products.	Dry heat is applicable for sterilizing glassware and metal surgical instruments and moist heat is the most dependable method for decontamination of laboratory waste and the sterilization of laboratory glassware, media, and reagents.
Chemical: Gaseous sterilization	Alkylation	Penetrating ability of gases	Gases being alkylating agents are potentially mutagenic and carcinogenic	Ethylene oxide gas has been used widely to process heat-sensitive devices.
Radiation: Radiation sterilization	Ionization of nucleic acids	It is a useful method for the industrial sterilization of heat-sensitive products.	Undesirable changes occur in irradiated products, an example is an aqueous solution where radiolysis of water occurs.	Radiation sterilization is generally applied to articles in the dry state; including surgical instruments, sutures, prostheses, unit dose ointments, and plastics.
Mechanical: Filtration sterilization	Does not destroy but removes the microorganisms.	It is used for both the clarification and sterilization of liquids and gases as it is capable of preventing the passage of both viable and non-viable particles.	Does not differentiate between viable and non-viable particles	This method is Sterilizing grade filters are used in the treatment of heat-sensitive injections and ophthalmic solutions, biological products, air, and other gases for supply to aseptic areas.