As far back as 400 BC, Hippocrates advised his students to smell their patients’ breath to detect if they were ill. Now, researchers in America have invented a system which does just that, only rather more scientifically. A new analyser uses nano-rays to determine the precise chemical composition of a person’s breath. From that it is able to detect the “signature” of any of 17 serious diseases, from kidney cancer to Parkinson’s disease. Exhaled breath contains nitrogen, carbon dioxide and oxygen, as well as small amounts of more than 100 other chemicals, but the relative amount of each substance varies depending on a person’s state of health. Writing in the journal ACS Nano, scientists describe how they analysed the results with artificial intelligence techniques to classify and diagnose the conditions. They found that each disease produces a unique volatile chemical breathprint, based on differing amounts of 13 components. They also showed that the presence of one disease would not prevent the detection of others. The technology allows for an inexpensive and portable breathlyser-style device, which costs as little as £24 and is able to screen for various diseases in a non-invasive way. Lead author Professor Hossam Haick, said: “We found that just as we each have a unique fingerprint, each of the diseases we studied has an unique breath print, a ‘signature’ of chemical components. “We have a device which can discriminate between them, which is elegant and affordable.” In recent years, scientists have developed experimental breath analysers, but most of these instruments focus on a single type of disease, such as cancer.