Answer: Biocidal Metals

If you’re the sort of person that puts even a little thought into the countless germ covered surfaces you come into contact with every day, we’ve got a bit of good news to put a dent in your apprehension over touching things in public.

Metal handles, door knobs, and other surfaces you interact with are naturally self cleaning, from a bacterial standpoint, thanks to a phenomenon known as the oligodynamic effect (from the Greek roots “oligos” or “few” and “dynamis” or “force”). While the mechanism of action is being continually researched and the theories regarding the biocidal properties of metal are being refined over time, the most prominent theories are that metals interact with protein groups (rendering them, by modification on a chemical level, unable to function), that various interactions between metals (especially heavy metals) and cell walls degrade the walls and destabilize bacteria, and that absorption of metals into the body of a cell disrupts key chemical reactions.

Practically speaking, what does this mean in the real world? It means that metal doorknobs, especially those made of copper or copper alloys like brass, destroy bacteria that ends up on them. E. Coli, for example, produces potent toxins and is a serious public health threat. On copper and copper alloy doorknobs (such as brass door knobs and handles) though, over 99.9 percent of E. coli microbes are killed after just 1-2 hours.

Not only does this mean the handles in old buildings are self-cleaning, but it also has implications in the design of hospitals and other germ-sensitive areas. Of the many metals that exhibit a strong oligodynamic effect, ironically, the metal most commonly found in the healthcare industry, stainless steel, does not (on which E. coli takes weeks, not hours, to die off). With this in mind, there is a push towards using metals with biocidal properties in hospital design for the protection of patients and staff alike.