Bad bugs detected by sensors

New sensors can detect 20 bacteria in five minutes, or a single
infected potato in a 25kg bag, two weeks before external signs
become visible.

Each task requires its own particular technology, but most problems
can be solved with low cost devices, provided the right technique
is chosen and sufficient effort is devoted to development.




Dr David Cowell, research director in the Faculty of Applied Sciences
at the University of the West of England (UWE), told Eureka that the
20 detectable bacteria are E Coli, fewer than 100 of which can
constitute an infective dose from contaminated food.

All aerobic and some anaerobic bacteria possess an enzyme called
catalase. This enzyme breaks down hydrogen peroxide resulting
from aerobic metabolism. Bacterial presence can then be detected
electrochemically from the amount of hydrogen peroxide remaining
in a solution, using a platinum electrode. Specificity, the ability to
distinguish one bacterium from another, can be achieved using
Lateral Flow Immunoassay, presently used in home pregnancy test kits.




Rot infected potatoes may be detected using a ceramic-based tin
dioxide sensor to respond to volatiles. Tin dioxide sensors are
widely used with neural networks to act as electronic noses. These
devices are, however, very expensive. The UWE sensor, on the
other hand, is much cheaper. A hand held sniffer has already been
constructed and tested as part of a project supported by the British
Potato Council. Once potatoes going bad can be detected, it is
possible to avoid the infection spreading. "One bad apple spoils
the whole bunch" applies to many types of foodstuffs. The UWE
team has successfully applied similar technology to detecting
off taints with 100% accuracy in Parma type hams and is conducting
research into applying the method to the detection of fungi in stored
grain.

Biosensors with immobilised antibodies are also proving useful.
Working with DEFRA and the Silsoe Research Institute, UWE is
developing sensors to look at progesterone levels in milk, with
a view to discovering the best time for insemination. The devices
use screen printed carbon based inks on PVC substrates, so are
fundamentally very low cost and disposable. Another sensor,
with the carbon electrode suitably impregnated and coated, can
be used to detect water polluting ammonium ions down to parts
per billion. Sensor shelf life is expected to be at least six months.

Dr Cowell believes it is possible to develop a biosensor to detect
almost any kind of organism or hormone, provided that sufficient
time and funds are available.
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