9 June 2005: Causing a stir in microfluidics

Bea Perks/Munich, Germany

The time it takes to analyse a blood sample could be slashed with a device that, in the words of its inventor, looks like a plastic coffee stirrer.

The prototype device, being developed at e2v technologies, Chelmsford, UK, uses a combination of microfluidics and Raman spectroscopy. Blood samples are taken when one end of the stirrer - in which a microlitre array has been embedded - is simply placed against the skin. 

The microlitre array is composed of a nickel and sucrose material arranged in a grid of 300 micro-needles. ’The dimensions of these are modelled on mosquito mouthparts,’ said Richard Gilbert, principal scientist in the biosensors group at  e2v. You don’t feel a thing, he says. The needles are about 150 micrometres long and 20 micrometres wide - long enough to reach capillaries and too short to reach pain sensors. The system takes a 20 nanolitre blood sample.

Once the sample is on board, nanolitre quantities of the buffers required for analysis are forced into microchannels by squeezing a fingertip-sized bulb at the far end of the stirrer. 

Blood is treated as it diffuses through the channels before entering a surface enhanced resonance Raman spectroscopy (SERRS) sensor, also fixed on the plastic stirrer. 

The SERRS system involves an array of metal spots with molecules attached to their surfaces. ’Essentially, it’s a very similar sensor to conventional microarray technology,’ said Gilbert - the molecules on each spot are equivalent to those coating each well in a microtitre plate. 

’When you shine a laser light at a spot, most of the light gets reflected (as you’d expect from a mirror), but some of the light gets scattered at random angles,’ said Gilbert.   ’This scattering isn’t due to imperfections in the surface, it’s due to molecules absorbing the photons that come in.and then reemitting the photon in a random direction.’ The pattern of reemitted light can be measured, and provides a unique fingerprint for different molecules.

Comparing SERRS against high performance liquid chromatography (HPLC), the gold standard for analysis, shows that the two give almost identical results. The big difference, said Gilbert, is that what SERRS does in an afternoon can take weeks with HPLC. 

Gilbert predicts that a final version of the system - which could be used to analyse protein, DNA or both at the same time - is about three years away. 

Its development relied on input from a wide range of fields: from materials scientists, nano-engineers and microfluidics experts to bioanalysts. ’Almost everything is really pushing the boundaries of each of the individual disciplines and there are so many points at which the whole thing could have gone horribly wrong,’ said Gilbert. Fortunately, he told the business congress Biotrends, they have yet to meet any major hurdles. 

’The next few years, whether or not we succeed, will be a very exciting time in the diagnostics field,’ he said.