Radiation is a physical method of sterilization that uses electromagnetic or particulate energy to damage microbial DNA/proteins, without generating heat — making it especially useful for heat-labile materials.
Types:
Non-ionizing radiation (Ultraviolet, UV) — wavelength ~240–280 nm (peak germicidal effect around 254 nm); acts by causing thymine dimer formation in microbial DNA, blocking replication and transcription; has poor penetrating power (only kills organisms on directly exposed surfaces, cannot pass through glass, most solids, or turbid liquids) and is used for surface disinfection of air in operation theatres, laminar flow cabinets, and laboratories; also used for water disinfection in some settings. A recognized occupational hazard is skin/eye irritation with direct exposure.
Ionizing radiation — gamma rays (from a Cobalt-60 or Caesium-137 source) and high-energy electron beams (cathode rays); both have high penetrating power, capable of sterilizing sealed, prepackaged items without opening them. They kill microorganisms by directly damaging DNA and by generating free radicals (from radiolysis of water) that further damage cellular macromolecules.
Industrial/medical uses of ionizing radiation (“cold sterilization”): sterilization of pre-packaged single-use medical disposables (syringes, catheters, sutures, surgical gloves), pharmaceuticals, and some heat-sensitive plastics/materials that would be damaged by autoclaving; also used for radiation sterilization/pasteurization of certain food products.
Advantages: no heat generated, so suitable for heat-labile items; can sterilize sealed packaging (no risk of post-sterilization contamination before use).
Limitations: expensive equipment/infrastructure (for ionizing radiation), potential for material degradation with repeated/high-dose exposure, and strict safety/shielding requirements for ionizing sources.
