It turns out that dealing with old paper money is a huge issue for the world’s central banks. The notes generally need to be destroyed and replaced since there has been no good way to clean them. Now scientists in Rhode Island have come up with a solution: use supercritical CO2 to clean the accumulated hand oils and dirt off of the old bills so they can be re-used.
Here’s the layman’s version of the story, from The Econmist: The Benefits of Money Laundering
Or, for you folks who prefer your science news unmediated by the press, here’s a reference to the research paper itself: http://pubs.acs.org/doi/abs/10.1021/ie403307y