(BBC News) Criminals are smuggling billions in US bank notes into Mexico every year, but help could be on the way for border guards.
A machine that can "smell" dollars - like a sniffer dog senses narcotics - is being developed.
For the first time, chemists have captured the unique fragrance of US paper money.
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They announced their discovery at the American Chemical Society meeting.
"Money sniffing is an unknown art. No-one had ever tried to find these aromas," said Dr Joseph Stetter, of KWJ Engineering.
"We found that US currency emits a wide range of volatile organic compounds that make a 'fingerprint' we can identify in less than a minute."