The new device, developed by researchers from Arizona State University in the US, uses a combination of uniform and non-uniform electric fields to separate particles according to their size, shape and charge amongst other properties.
The device makes use of a technique known as direct current insulator dielectrophoresis (DC-iDEP) to provide sequential, spatially resolved separations by simultaneously exploiting electrophoretic (EP), electroosmotic and dielectrophoretic (DEP) transport mechanisms.
"We envisage this technique could impact any place where the properties of particles are of interest for separation - based on first principle arguments there is no reason why cancer cells or viruses couldn't be pulled out of complex biological systems," said Dr Mark Hayes, lead author of the paper that will appear in an upcoming issue of Analytical Chemistry.
The separation of biological particles by electrophoresis is widely used by industry and causes charged particles to move under the influence of an electric field. The technique does have some limitations and depends primarily on the charge to size ratio of the particle.
Dielectrophoresis exploits the force exerted by a non-uniform electric field on a polarisable particle and has been used to separate cancer cells from blood cells, live cells from dead cells and cells invaded by parasites from normal cells.
There are inherent problems with this approach as well with the electrodes embedded within the separation chamber causing undesirable electrochemical reactions and gas generation.
"Electric field forces are simple when they linear and not so simple when they are not and with this complexity comes possibilities," said Hayes.
Hayes and Dr Michele Pysher developed the device to overcome these problems and enhance separating efficiency and specificity by combining both electrophoretic and dielectrophoretic forces.
The device uses a microfluidic channel with walls that have a 'saw tooth' pattern.
Each pair of opposing teeth establishes a local gradient region that act as individual dielectrophoretic traps with the width, height and angle of the teeth determining the strength of each trap.
The device was designed so that the strength of the traps gradually increased along the length of the channel.
This allowed the separation of live and dead Bacillus subtilis cells labelled with different fluorescent dyes, with the live cells being isolated first in the weaker DEP traps and the dead cells being isolated in the stronger traps.
"The only limitation is that the technique will only work for charged species, but all particles carry some charge even if only a dipole," said Hayes.
The current device used in-situ fluorescence detection, but Hayes believes that "there is no inherent limitation of the detection methods available once you flow the materials out of the chip".
He continued by explaining that this could be achieved in two ways - either by pumping out the particles down the length of the channel by turning the field off, or by sending the particles down microfluidic channels that could be built into certain parts of the device.
Hayes did caution that: "the underlying theory is pretty under-developed and we don't know how good (or bad) this technique could be - experimentally the theory has been exceeded which gives us the opportunity to develop new theories!"
He was also quick to praise early work in the field from researchers at the Sandia National Laboratories in the US who conducted some of the pioneering experiments in the area.
