Measuring the Force Gradient Acting on a Magnetic Microsphere above a Micro-Magnet Array

Abstract : The attractive action exerted by an array of micro-magnets on a single polystyrene microsphere containing superparamagnetic iron oxide nanoparticles, the microsphere constituting a model for cells functionalised with such nanoparticles, have been studied in air by using magnetic force microscopy. For this purpose, the method of gluing a magnetic microsphere to an AFM tip has been developed. Using this custom-made colloidal probe, the regions of the micro-magnet array that act as magnetic traps for the magnetic microsphere have been localized and the long-range trap-sphere interactions have been recorded, measured and compared with simulations.