A microfluidic device that can identify exposure to sarin could help identify individuals needing treatment at sites of terrorist attack.

Trace amounts of sarin inhibit an enzymatic reaction on the chip

A lab on a chip that can detect traces of sarin and related neurotoxins in a small drop of blood has been made by Nam-Trung Nguyen at Nanyang Technological University in Singapore and colleagues at DSO National Laboratories, Singapore. Nguyen says that the device would allow the first responders to a terrorist strike, such as the 1995 Tokyo subway sarin attack, to quickly distinguish the 'worried well' from genuinely exposed individuals requiring treatment.

'Our device integrates an entire protocol for the detection of trace amounts of nerve gas agents in blood,' says Nguyen. 'One of the challenges is using whole blood as the sample - the device needs to handle several tasks, from blood sample preparation to final optical detection.'

The blood flows through the chip in a sequence of steps. Initially, the blood cells are burst open and the sarin released, before the blood proteins and other particulates are filtered out. The purified mixture is then mixed with a substrate and a chromophore, and passed over an immobilised enzyme. If the sample contains no sarin, the enzyme reacts with the substrate, which then attacks the chromophore, which is detected by an external UV-visible spectrometer. But if sarin is present it inhibits the enzyme, so the chromophore passes to the detector unchanged.

'The device can also be used to detect organophosphorus insecticides, so it could find further applications for occupational hygiene in agriculture,' adds Nguyen. 'A simple, low-cost device for evaluating the degree of insecticide contamination could be important for rice-producing countries. Together with other future water technologies, our technology could be crucial for securing and providing clean water sources for the population.'

Jonas Berquist studies chip-based blood analysis at Uppsala University in Sweden and says he is impressed with the number of steps integrated into the device. He points out that the next step would be to remove the need for an external detector. 'It's a problem not many people have solved yet,' he says, 'but for a first screen device, it would be nice to have something easily detected [by eye], like a colour change.'

James Mitchell Crow