Scientists at Cambridge University have developed a biological sensor for detecting heroin which can identify individual particles of the drug measuring just thousandths of a millimetre.

The work at the university's Institute of Biotechnology has been backed by HM Customs and Excise, which is desperate for more sensitive ways of detecting illicit drugs. But Chris Lowe, a researcher at the institute, says that commercialisation will have to wait until the sensor can detect other illicit drugs such as cocaine.

The sensor relies on enzymes that enable certain bacteria to grow on a heroin-only diet. These enzymes are used by the sensor as a detector. If heroin is present in a sample, the enzymes degrade it. The accompanying molecular changes are registered by a transducer which converts the biological signal into an electrical signal.

The team has already succeeded in reducing the device to a simple colour test strip which turns red when heroin is present.

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But while the sensors used for detecting illicit drugs will have to wait, another application of the same enzymes has emerged. Dr Lowe says that the researchers are developing painkillers -- such as those derived from morphine -- biologically for the first time.

"The problem with chemical routes is that they are expensive and side reactions diminish yield. A biological route would be more cost-effective and its greater selectivity would mean yields are much higher," he says.

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The work has won funding from the Leverhulme charity and the Government under its Realising Our Potential Award scheme. Neil Bruce, who heads the project, says that the team is thinking in terms of kilogram quantities for the morphine-derived drug, hydromorphine. This has seven times the painkilling power of morphine and accounts for a fifth of the opiate medical market.

The technique could also produce the codeine derivative, hydrocodone, a cough treatment.