AN ELECTRONIC nose can identify people with lung tumours simply by sniffing their breath. While some cancer experts are sceptical, the creators of the e-nose at the University of Rome hope it could lead to the development of a simple breath test for the early detection of the disease.
A variety of conditions can lead to specific compounds turning up in the breath. For example, aliphatic acids show up in the breath of people with liver cirrhosis, while di- and trimethylamine are found in the breath of those with failing kidneys. Lung-cancer patients exhale a cocktail of alkanes and benzene derivatives, though no one is yet sure why.
Gas chromatography and mass spectrometry are normally used to analyse gas mixtures, but these techniques are too expensive and elaborate to provide a practical diagnostic test. Electronic noses are already used for quality control in the food industry. Now the researchers in Italy hope their e-nose could provide a diagnosis.
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Like an animal or human nose, the electronic version uses an array of sensors that are not designed to detect any one chemical. Instead they respond to the overall profile of compounds in a sample. In the food industry, this allows them to spot subtle 鈥渙ff鈥� smells and tastes.
The sensors are quartz crystal, each coated with a slightly different metalloporphyrin that binds to a different range of volatile organic chemicals. The crystals鈥� natural vibration frequency is related to their weight. This changes as molecules from the sample stick to their coated surfaces, so a complex gas sample such as human breath will create a unique profile of vibrations from an array of crystals.
A trial in Rome, results of which will soon be published in Biosensors and Bioelectronics, used an eight-sensor nose to build up vibration profiles for each breath sample. Sixty people at the Forlanini Hospital took part, 35 waiting for an operation to remove a large lung tumour and the rest controls. Each test took just over a minute and the nose successfully pinpointed every cancer patient.
The team鈥檚 next step will be to boost the sensitivity of the e-nose to detect tumours at a much earlier stage. To make a positive diagnosis of lung cancer, doctors currently use an invasive instrument called a bronchoscope to take a look inside the patient鈥檚 lungs and perhaps remove tissue for a biopsy.
Carrado Di Natale, the electronics expert developing the e-nose, says doctors might one day use a hypersensitive version of the device to screen smokers and other high-risk groups for lung cancer as part of a routine check-up. He thinks a breath tester could be made so simple that patients who have had surgery to remove a lung tumour could later test themselves at home. 鈥淚t would be less accurate than bronchoscopy but it would be so much easier,鈥� he says.
But Richard Sullivan, head of clinical programmes for the charity Cancer Research UK, is sceptical. 鈥淪mell is very important for detecting disease and this is an interesting twist,鈥� he says. 鈥淏ut this study is much too small to mean anything.鈥� Sullivan adds that even an extremely sensitive nose could only ever detect tumours on the surface of the lungs, so it could never replace the blood tests or scans needed to alert doctors to the onset of secondary tumours.