The invention discloses superparamagnetic monodispersed particles, their method of preparation and their uses. These particles comprise: a core of a first polymer, an internal layer of a second polymer coating the core, and in which is distributed a magnetic material, and an external layer of a third polymer coating the magnetic layer, and capable of interacting with at least one biological molecule, at least the second polymer being heat sensitive and having a predetermined lower critical solubility temperature (LCST) of 15 to 65 DEG C.