Pavel Kuzhir - Institute of Physics of Nice - Keywords: colloids, phase transitions

Pavel Kuzhir - Institute of Physics of Nice - Keywords: colloids, phase transitions

Contribution title: Magnetic filtration of phase separating ferrofluids: first steps towards application to detection of biomolecules

In this talk, we briefly review magnetic separation of ferrofluids composed of large magnetic particles (about 50 nm of the average size) possessing an induced dipole moment. Such ferrofluids exhibit field-induced phase separation at relatively low particle concentrations (0.8%vol.) and magnetic fields (10 mT). Particle aggregates appearing during the phase separation are extracted from the suspending fluid by magnetic field gradients much easier than individual nanoparticles in the absence of phase separation. Nanoparticle capture by a single magnetized microbead and by multi-collector systems (packed bed of spheres and micro-pillar array incorporated into a microfluidic channel) has been studied both experimentally and theoretically. Under flow and magnetic fields, the particle capture efficiency decreases with an increasing Mason number for all considered geometries. This decrease may become stronger for aggregated magnetic particles than for individual ones if the shear fields are strong enough to provoke aggregate rupture. These results can be useful for development of new magneto-microfluidic immunoassays based on magnetic nanoparticles offering a much better sensitivity as compared to presently used magnetic microbeads. The first steps towards realisation of such immunoassays consist in understanding the role of the thickness and grafting density of molecular layers (for instance detection antibodies adsorbed on nanoparticle surface) on phase separation and capture efficiency of functionalized nanoparticles.
This work has been supported by UCA programs of Academy 2 and "action du site".