Characters in television crime programmes will often get DNA profiling data back in the time it takes for you to boil a kettle, but in reality the process is much slower. Now, UK scientists at the University of Southampton and the Laboratory of the Government Chemist, Teddington, are working on a technique that could allow DNA evidence to be profiled at the scene of a crime.

DNA profiling doesn't sequence an entire genetic code - the Human Genome Project that finally did this took 13 years. Instead, the process searches for segments of DNA called short tandem repeats, or STRs, repeats of 2-6 DNA base pairs which appear throughout our genetic code. The number of times that each STR repeats varies from person to person, and so, by measuring the length of different STRs, you can identify an individual.

The approach taken by Tom Brown and colleagues exploits the fact that DNA of different lengths unwinds at different temperatures. The group reacts sample DNA with HyBeacons, small DNA sections with fluorescent probes attached. The HyBeacons bind to STR DNA and fluoresce as the probes are no longer free to interact with each other and quench fluorescence. When the sample is then heated, the STR sections of DNA unwind, the HyBeacons and STR-containing DNA separate and the fluorescence stops; the temperature at which this happens indicates the number of STR repeats.

Until now, STR lengths were measured by seeing how far they passed through a gel: the longer the strand the slower it moves and the shorter distance it travels. However, to have enough DNA for analysis, the STRs have to be copied many times and so the entire profiling process takes about a day in a laboratory. Using HyBeacons requires much less DNA and so eliminates the need for this time-consuming copying process.

'This is an elegant approach,' says Duncan Graham, of the University of Strathclyde, Glasgow, UK, who works with chemically modified DNA. 'It offers significant advantages for forensic applications such as DNA fingerprinting.'

Indeed, the next goal for the team is developing the equipment to optimise the DNA analysis. 'DNA profiling has transformed forensic investigations over the past twenty years,' explains Brown. 'But,' he adds 'a holy grail is for the technology to become so rapid and portable that it can be applied at the point of crime, or suspect arrest.' 

Laura Howes

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