Technology: . . . while lasers sniff out stomach ulcers

 作者:有缸溺     |      日期:2019-02-28 01:11:03
By JONATHAN BEARD in NEW YORK People with suspected stomach ulcers could get the results of tests within a few minutes without leaving their doctor’s surgery, thanks to an instrument which can detect the ratio of carbon isotopes in their breath. The new device, which is based on a carbon dioxide laser, is as accurate and sensitive as laboratory instruments that cost tens of thousands of dollars more, according to its inventor, Daniel Murnick, of Rutgers University, New Jersey. The instrument developed by Murnick and Brian Peer, who worked with him as an undergraduate assistant, can compare the ratios of two isotopes of carbon – carbon-12 and carbon-13 – in a gas sample. ‘We use a tunable carbon dioxide laser to irradiate the sample gas,’ Murnick explains. ‘When stimulated by the laser light at the correct wavelength, a carbon dioxide molecule changes its excited state in an electrical discharge, yielding an electrical signal.’ Different signals are obtained for carbon dioxide containing the two carbon isotopes. The instrument measures the ratio of the two signals to determine how much carbon-13 the sample contains. The instrument can detect stomach ulcers in a simple test, says Murnick. A patient is given a small amount of urea (CO(NH2)2) in which the carbon is enriched with the stable, nonradioactive isotope carbon-13. Helicobacter pylori, a bacterium which often lurks in the stomach lining and is known to be the cause of many ulcers, can metabolise urea in the stomach, which leads to the production of carbon dioxide. In an uninfected stomach, the urea would not be broken down, and pass to the intestines. In the diagnostic test, the patient is given the sample, and after 20 to 40 minutes, gives a sample of their breath by exhaling into a tube. Normally, carbon-13 accounts for only about 1 per cent of carbon atoms. If the laser device detects a spike of carbon-13 in the sample, this is evidence that the person is infected with H. pylori. It has been known for years that the bacterium metabolises urea, Murnick says. Previous tests have sometimes used urea labelled with radioactive carbon-14 and so exposed the patients to a radiation hazard – albeit a slight one – and produced radioactive waste. If carbon-13 was used to label urea, expensive laboratory mass spectrometers were needed to detect it. Diagnostics and Devices, a New Jersey medical instrument company, has licensed Murnick’s idea and plans to manufacture early versions within the next year. Detecting ulcers is just one of many possible applications for a quick, inexpensive method of determining isotope ratios: ‘Many other medical conditions involving the liver, colon and other organs could be diagnosed this way,’ Murnick says. ‘For example, we could label glucose, lactose or caffeine with carbon-13, and monitor the carbon dioxide the patient breathed out.’ Pollution control is another area where sensitive detection devices are needed. Scientists checking the levels of pollutants in water now use mass spectroscopy to compare isotope ratios in polychlorinated hydrocarbons, for example. ‘Instruments based on our technology should be inexpensive and small enough to be used in research ships and vans,