Your breath says a lot about you. Ancient medicine recognised this, as did Dr James Payne, inventor of the breathalyser. Electronic noses are now diagnosing all kinds of diseases. British company Osmetech has made a nose that detects six of the seven bacteria that cause urinary tract infections, in two hours instead of the usual 24.
Nathan Lewis, a chemistry professor at the California Institute of Technology and a pioneer in this field, has developed simple polymer films that are a mix of conductor and insulator. When exposed to gaseous chemicals, the films absorb certain molecules, swell, and so increase their electrical resistance. Clever pattern recognition software, different polymer films and an array of sensors enable the nose to smell more than just halitosis. Potentials outside healthcare include food diagnosis and quality control of recycled plastics.