Which of the following sterilisation methods achieves sterilisation primarily through the production of free radicals and ionisation of molecules?

Explanation

## Mechanism of Gamma Radiation Sterilisation **Key Point:** Gamma radiation (ionising radiation) sterilises by producing free radicals and directly ionising cellular DNA and proteins, leading to irreversible damage and microbial death. ### Physical Basis Gamma rays (from Cobalt-60 or Cesium-137) are high-energy electromagnetic radiation that: 1. Directly ionise DNA molecules, causing strand breaks 2. Indirectly generate free radicals (•OH, •O₂⁻) in aqueous environments 3. Damage microbial cell membranes and proteins 4. Require no gas residues or heat — ideal for heat-sensitive materials ### Comparison of Sterilisation Methods | Method | Mechanism | Temperature | Gas Residue | Best For | | --- | --- | --- | --- | --- | | **Gamma radiation** | Ionisation + free radicals | Ambient | None | Plastics, pharmaceuticals, implants | | Ethylene oxide | Alkylation of proteins/DNA | 37–60°C | Yes (toxic) | Heat-sensitive items | | Dry heat | Protein denaturation + oxidation | 160–180°C | None | Glassware, metals | | Filtration | Mechanical removal | Ambient | None | Liquids, gases (not sterilisation per se) | **High-Yield:** Gamma radiation is the **gold standard for pre-sterilised medical devices** (syringes, catheters, implants) because it penetrates packaging and leaves no residue. **Clinical Pearl:** Unlike ethylene oxide, gamma radiation does not require aeration time post-sterilisation, making it faster for large-scale industrial use.