Aldehydes. Two aldehydes, formaldehyde and glutaraldehyde, inactivate microbial proteins by crosslinking the functional groups in the proteins. Formaldehyde gas is commonly used as formalin, a 37 percent solution of formaldehyde gas. It is widely employed for embalming purposes. Glutaraldehyde is used as a liquid to sterilize hospital equipment. However, several hours are required to destroy bacterial spores (Figure 1 ). Ethylene oxide. Sterilization can be achieved with a chemical known as ethylene oxide (ETO). This chemical denatures proteins and destroys all microorganisms, including bacterial spores. It is used at warm temperatures in an ethylene oxide chamber. Several hours are needed for exposure and flushing out the gas, which can be toxic to humans. ETO is widely used for plastic instruments such as Petri dishes, syringes, and artificial heart valves (Figure
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