Infrared Avacta detector

2 min read

Physicians have known for millennia that the smell of human breath can reveal certain medical conditions. Until now it has been a subjective assessment based on the nasal sensitivity and experience of the doctor. But that may change with the development of a device that can detect a tell-tale odour from a patient and diagnose their condition.

The prototype detector works by identifying the presence of molecules of gases that are responsible for the distinguishing odour. For example, acetone smells like rotten fruit and can be a result of one form of diabetes. A whiff of fish could be caused by cirrhosis of the liver.

Gathering such medical evidence reliably should simplify and accelerate patient diagnosis. However, while it is one thing knowing which molecules create which smell, it is another detecting them scientifically and affordably. The consequences of false positives and negatives may be grave, so any instrument has to be accurate.

The new detector uses infrared laser light to do the job. It is being perfected by Avacta, a York-based biophysics company spun out from Leeds University in 2004 which, last year, acquired Oxford Medical Diagnostics, where the technology had been developed originally.

The principle is straightforward. 'Gaseous molecules will absorb infrared light at different wavelengths depending on what the molecule is,' said Chris Dryden, Avacta commercial director. 'So, if you have a very precise wavelength emitted by a laser and you can measure how much light is absorbed, it becomes possible to detect how much of a particular gas is present.'

Avacta's process takes place inside a cylinder. It has mirrors at each end to bounce a beam of infrared light to and fro through the sample of breath, multiplying the path length and increasing the sensitivity of the machine. The system knows how much power it puts into the infrared light and a photo detector measures the remaining power after some of it has been absorbed by the molecules within the sample. The difference between the original and resultant power reveals the amount of the diagnostic gas in the breath.

This technique, called cavity enhanced absorption spectroscopy, is not limited to detecting gases that have an odour that can be smelled by the human nose. The prototype has been tuned to quantify methane, a molecule that can indicate irritable bowel syndrome. It can also analyse the ratio between two isotopes of carbon (C12 and C13) in carbon dioxide, a figure that can reveal the presence of H. pylori bacteria, which is responsible for stomach ulcers.

The only breath diagnostic test so far approved by the US Food and Drug Administration detects the carbon isotope ratio and Avacta is looking to see if its technology can do the task better. However, it is more interested in detecting other breath 'markers' so it has recently entered into a collaboration with V&F Medical Development, an Austrian producer of high-quality mass spectrometers.

V&F's role is to identify the markers for selected bacterial infections, some of which may be distinguished by more than one marker and at different concentrations. Then it will determine which light sources should be used in Avacta's products to supply the optimum wavelengths and detect those markers most efficiently.

Avacta would like to be able to use lasers that are found already in consumer electronics or telecommunications because they would be readily available and relatively cheap. The eventual aim is to have an instrument that is sufficiently versatile, simple and affordable to be used by nurses in doctors' surgeries to perform swift breath tests.

Avacta chief executive Alastair Smith believes the potential size of the markets for clinical analysis of breath gases is large. 'Clinical diagnostics products are still in early development stages but this collaboration with V&F and the completion of the prototype breath analysis system brings us significantly closer to market and is a major step forward in achieving our clinical diagnostics ambitions,' he said.

Max Glaskin