A magnet-driven microchip can rapidly and reliably replicate DNA, for many uses including forensic investigation at crime scenes.

The polymerase chain reaction (PCR) is a tool for replicating DNA. Copies are made by passing DNA fragments through three different temperature zones; each cycle doubling the amount of DNA.

The miniature PCR device designed by Nam-Trung Nguyen and colleagues at Nanyang Technological University, Singapore, is simpler and more reliable than existing methods because magnetic force is used to drive the DNA sample around the microchip rather than a pump mechanism. Pumps are expensive and put high mechanical requirements on the microchip as the channels have to withstand high pressures.

In Nguyen's system, the DNA sample flows continually through a circular closed loop, driven by a plug controlled by an external permanent magnet. As the sample goes around the microchannel loop it passes through the three temperature zones. 'Successful PCR was achieved in less than 4 minutes,' said Nguyen.

The time taken for the fluid to cycle around the zones can be adjusted by changing the speed of the external magnet. According to Nguyen, the magnet is a good way to drive the system as it is low cost, has small power consumption and a flexible number of PCR cycles.

'Other similar designs face problems of temperature control, high driving pressures and leakage,' said Nguyen, 'but the implementation of this chip in a complex lab-on-a-chip system should not have these issues.'

'Our aim is to develop an integrated system for fast screening of DNA samples at a crime scene,' said Nguyen.

Alison Stoddart