Development of a novel magnetophoresis-assisted hydrophoresis microdevice for rapid particle ordering

Focusing and ordering of micro- or nanoparticles is an essential ability in microfluidic platforms for bio-sample processing. Hydrophoresis is an effective method utilising hydrodynamic force to focus microparticles, but it is limited by the fixed operational range and the lack of flexibility. Here, we report a work to tune and improve the dynamic range of hydrophoresis device using magnetophoresis. In this work, a novel approach was presented to fabricate the lateral fluidic ports, which allow the flipped chip to remain stable on the stage of microscope. Diamagnetic polystyrene microparticles suspended in a ferrofluidic medium were repelled to the lower level of the channel by negative magnetophoretic force, and then interact with grooves of microchannel to obtain an excellent hydrophoretic ordering. The effects of (i) flow rate, (ii) particle size, (iii) magnetic susceptibility of the medium, and (iv) number of magnets on the particle focusing efficiency were also reported. As the proposed magnetophorsis-assisted hydrophoretic device is tuneable and simple, it holds great potential to be integrated with other microfluidic components to form an integrated sample-to-answer system.