Some biomedical applications of ferrofluids

Ferrofluids are colloidal solutions of iron oxide magnetic nanoparticles in either a polar or no polar liquid. We present here two biological applicat ions using maghemite (gamma Fe2O3) ferrofluids: magnetic cell sorting and m agnetocytolysis. The first application employs magnetic particles binding a biological effector; which is capable to recognize the target cells specif ically. These cells become magnetic and can be sorted in a gradient of magn etic field. We describe first the various steps of the synthesis of a bioco mpatible ferrofluid and the grafting an effector protein onto the particles . We then describe the use of particles carrying annexin V in the separatio n and quantification of damaged erythrocytes in blood samples. This very se nsitive technique can be used to follow the erythrocytes ageing of normal b lood samples during their storage under blood bank conditions of to detect the membrane modifications that are associated with some pathologies such a s malaria or Alzheimer's disease. The dependence of the magnetic susceptibi lity versus the frequency is a way to transform magnetic energy into therma l energy. Magnetocytolysis is the destruction of cells, carrying magnetic p articles, through the action of an alternating magnetic field (about 1 MHz) . We present here preliminary experiments with macrophages, which demonstra te the method's feasibility and the formation of the non-specific interacti ons between the cells and the magnetic particles.