Bad bugs detected by sensors

New sensors can detect 20 bacteria in five minutes, or a single infected potato in 25kg, 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 in the West of England, 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 kind 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 sufficient time and funds are available. Design Pointers * Electrochemical sensors shows potential to make devices capable of detecting 20 bacteria * Tin dioxide sensors can detect volatiles from a single infected potato with no visible problems in a 25kg bag * Sensors with impregnated carbon electrodes can measure traces of pollutants down to parts per billion University of the West of England Faculty of Applied Sciences