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.
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For more information, please contact:- Osmetech
November 2000
