Rapid and efficient mixing of particles in a microfluidic system is of great interest for chemical and biochemical analysis, especially in miniaturised lab-on-a-chip platforms. In the larger scale, mixing relies on turbulence and chaotic stirring of the fluid. This is commonly achieved in laboratories by using rotating magnets to move magnetic stirrers. However, this kind of contactless actuation is difficult to implement in a small lab-on-a-chip device. In the small scale, mixing is not as straightforward because the large-scale friction forces make fluid flow laminar and stable. Furthermore, most biological particles such as cells are non-magnetic and do not respond to a magnetic field.

Prof. Nam-Trung Nguyen’s team at the Queensland Micro- and Nanotechnology Centre of Griffith University solved these problems by utilising a magnetofluidic phenomenon called diamagnetophoresis.

“Magnetism can stir particles if there is a mistmatch in magnetic properties between the particles and the surrounding fluid. The particles do not need to be magnetic. We can make the surrounding fluid magnetic to move non-magnetic particles around in the small scale,” said Ahmed Munaz, the first author of this research.

The team developed a microfluidic device with a set of external rotating magnets. The magnets create a complex rotating magnetic field that can efficiently mix multiple non-magnetic samples dispersed in magnetised fluid. The team’s microfluidic platform achieved 86% mixing efficiency.

“With the fabrication support from ANFF-Q, we are able to design and fabricate the device prototypes within just a few days. The quick turnaround enables the optimisation of our mixing concept and the verification of numerical simulation data,” said Mr. Munaz.

“Our proof-of-concept results pave the way for the implementation of an all magnetofluidic lab-on-a-chip platform that uses magnetism for contactless sample preparation steps such as mixing and separation of biological particles such as cells, exosomes and DNA fragments.”