APPLICATION STORY

 New Electronic Nose which can smell out gases.


Polymer membrane sensor arrays - also called 'electronic noses'
- have been a promising technology for several years.
Chemists hope they could be a simple alternative to many of the
complex instrumental techniques, such as chromatography and
ultra-violet spectroscopy, that take up so much time in both industrial
and clinical labs.

Success now seems to be close, after news of successful trials of the
technology at hospitals in Manchester and London to diagnose the medical
condition, bacterial vaginosis.


 The analyser instrument consists of
 an array of 48 of these conducting
 polymer sensor elements, made
 using wafer scale technology.
 The array is selected to match the
 particular application.
Bacterial vaginosis (BV) is an unpleasant and dangerous infection that affects many pregnant women, and can cause premature birth or miscarriage. It is very prevalent in the US, where about one in five mothers are infected. But there has never been a diagnostic technique fast enough to allow effective antibiotic treatment. The usual method is to take swabs and grow the bacteria on culture dishes, which can take three days and costs £12 per test. A company called Osmetech has now designed an electronic nose customised to smell out the gases emitted by the bacteria which cause BV. Even more important, Osmetech has shown that its "nose" is just as accurate as the old method, while taking only five minutes to produce a result. Early in October, the company announced that a large-scale trial on 1,038 patients at St. George's Hospital in London showed that its microbial analyser matches the accuracy of the "gold standard" culture dish technique. It rapidly identifies the vast majority of affected women and indicating which have to be treated with antibiotics. Through its US subsidiary Aromas-can, the company now intends to apply for a licence to market the device in the US, where the potential market is huge - up to ten million examinations each year. How, then, does it work? Conducting polymers are made by 'electropolymerisation' of complex organic dyes- specifically, derivatives of the substances polypyrole, polyaniline and polythiophenes. Osmetech has discovered how to give each polymer a different conductive behaviour depending on its exact chemical structure, so that it has managed to build up a proprietary library of 80 to 100 sensor materials, with each element testing for a particular molecular type. When these polymers come into contact with analyte molecules, their conductivity changes, creating a current within the sensor that is proportional to the concentration of the analyte. These currents are picked up by signal processing circuits in the instrument, and compiled into a response profile (or 'scent') that characterises the atmosphere around the sensor. The analyser instrument consists of an array of 48 of these conducting polymer sensor elements, made using wafer-scale technology. The array is selected to match the particular application: for example a narrow range of sensor types would be chosen to obtain very high sensitivity where only a few chemical species need to be assayed. A module containing a broad range of different sensors would be used where many dlifferent responses are needed to detect a wider range of analytes. BV is not the only medical application. The company is sponsoring St. Thomas Hospital in London to try out another version of its nose in the diagnosis of urinary tract infections (UTIs). This too shows great promise, says Osmetech's chairman Gordon Hall: "The study confirmed that the microbial analyser can reliably detect the six most common pathogens, responsible for 98 per cent of all UTIs". The UTl market is potentially huge too: 500 million urine culture tests are carried out worldwide each year, most of them negative for infection. All are labour intensive and take about 24 hours to yield results. The sensor array, which began feasibifity studies at the Brigham and Women's Hospital at Harvard in the US in January, produces results within two hours. According to Professor Andrew Onderdonk, who is leading the studies: "The issue is not whether the Osmetech technology will work for detecting bacteria in urine, but how best to implement this technology." Industrial uses... An electronic nose also has many ndustnal applications - which unlike clinical tests rarely need regulatory approval and so have been more quickly implemented. The most obvious industrial application for an electronic nose is, naturally, aroma. Food and toiletries makers use panels of humans to assess the smell of their products, but such panels can never be entirely objective or reproducible. Electronic noses can be objective, and polymer sensors are now being used to sniff out the amount of ethanol in mouthwash, monitor odour levels in sodium bicarbonate for toothpaste, check the stability of fragrance in soap tablets, and assess the smell of the fixatives used in hair sprays. Another application is in cereal quality assurance.. Specialty trained human sniffers have been used for hundreds of years to detect the presence of mould and contaminants in bulk grain stores. This is particularly important in the Far East, with its large rice consumption; rice stored for a long time can acquire unpleasant tastes and smells, which significantly affect its price. The polymer sensor array can perform this sensing role and supply some consistency in assessing the quality and value of the rice. Polymer sensor arrays are also being used to check the usability of recycled plastics, which are nowadays popular materials for manufacturing car interiors. Such plastics can retain traces of smells from their previous uses, which are not necessarily welcome inside a car on a hot day. The Osmetech sensors can detect these trace odours in two hours instead of the hours needed for gas chromatography - and in a "real" vehicle environment, too, not just in the lab. ___________________________________________ For more information, please contact:- Osmetech November 2000
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