The new device, described in an early view article in Analytical Chemistry , can be used to perform complex-separation tasks such as the fractionation of red blood cells, platelets and leukocytes.

The technique, dubbed free flow acoutophoresis (FFA) by the authors from the Lund Institute of Technology and Lund University Hospital in Sweden, uses an ultrasonic standing wave coupled to a laminar flow in a microfluidic device to separate particles by their size and density.

The separation of suspended (sub-)micrometer-sized particles is of fundamental importance to the biological sciences where separating cells is still a challenge.

The most widespread method for cell and particle separation is centrifugation which also exploits differences in the particles size and density.

However this method exerts substantial mechanical stress on the sample and can damage the biological samples.

Initial tests involved separating polystyrene spheres of various sizes in the microfluidic device before moving on to more complex biological systems.

No significant separation of red cells and platelets was observed in normal saline solution, however, according to the authors: "when CsCl was added to the saline solution, it resulted in near perfect separation of the two blood cell constituents."

With the authors noting that: "there were no indications of damage to the red cells during the blood component separation experiments."

This approach was then extended to separating 'buffy coat' and intermediate fraction from whole blood units that contains red blood cells, platelets and leukocytes where the addition of CsCl allowed significant separation to be achieved.

The authors write that: "the results strongly indicate that it is possible to obtain pure fractions of the different blood cells simultaneously… by using more parallel outlets, a balanced suspending medium and a slightly stronger acoustic force field, good separation results should be feasible."