Positively arresting

A DNA purification technique based on magnetic separation could help forensic scientists and police to speed up criminal investigations, its UK developer has claimed.

Kent-based DRI said its Charge Switch Technology (CST), which uses sub-micron-sized magnetic beads to bind DNA and separate it from extraneous matter around it, would allow high-quality samples to be taken from common debris such as hair, blood spots and cigarette butts found at crime scenes.

DNA has to be extracted and purified before it can be compared to other samples, a process normally involving a number of stages and a variety of substances – some of them hazardous to handle.

CST works by supplying a switchable positive charge to a surface containing DNA material. When applied along with chemical reagents and the magnetic beads, the charge binds high density, negatively charged nucleic acid molecules to the surface.

It does not bind as strongly with proteins and other contaminants present on the surface, allowing these impurities to be washed away.

The addition of a further agent ‘switches off’ the charge, releasing pure DNA for analysis.

DRI, which is currently distributing prototype CST kits to forensic science services around the world, claimed that its technology is an advance on existing purification systems in several key respects.

Steven Ripley, the company’s marketing manager, said the application of CST to forensics would allow more reliable isolation of DNA from very small samples of evidence found at crime scenes.

‘We’ve proved that it works on very small quantities of material and performs consistently,’ said Ripley.

Unlike existing DNA purification techniques CST does not rely on the use of alcohols or other organic solvents, and the sample does not need to be heated or dried. All of these can have an adverse effect on the quality of DNA samples when they come to be analysed, in some cases rendering them useless.

CST also eliminates the need for centrifugation, a particularly labour-intensive and time-consuming component of the purification procedure.

According to Ripley, the CST-based process is highly suitable for automation, opening the way for quick, cost-effective processing of thousands of DNA samples by laboratory robots.

Rapid processing of DNA can be crucial in major investigations, for example where material from a serious crime scene is compared with samples taken from the local population.

Such ‘sweeping’ of thousands of people has been carried out by police forces on a number of occasions since DNA analysis first emerged as a criminal investigation tool in the late 1980s.

This is the first time the technology has been specifically applied to forensics.

DRI has spent several years developing various applications for CST for general laboratory use by the life sciences industry.

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