Influence of polyelectrolyte chains on surface charge and magnetization of iron oxide nanostructures

The layer-by-layer (LbL) technique was employed to encapsulate maghemite (γ-Fe2O3) nanoparticles with natural and synthetic polyelectrolytes, with a view to producing magnetic nanoplatforms as a tool to improve remotely assisted delivery/release of hydrophobic drugs and to address their low cargo capacity. Magnetic nanoparticles (MNPs) were synthesized by coprecipitation and functionalized with the layer-by-layer (LbL) assembly of polyelectrolyte multilayers. Simultaneous conductimetric and potentiometric titrations were utilized in order to find the optimal pH for the deposition of four intercalated layers of polystyrene sulfonate (PSS)/polyallylamine hydrochloride (PAH) or sodium carboxymethylcellulose (CMC)/chitosan (CHI) polyelectrolytes. XRD, TEM, DLS, TGA and FTIR techniques were utilized to access structural, morphological and surface properties. Charge reversals after each deposition confirmed a stable LbL assembly adsorbed on a multiparticulate nucleus (∼64 nm) of 8.8 nm-sized MNPs. Polymer layers of increasing thickness ranging from 4 to 15 nm (PSS/PAH) and from 21 to 48 nm (CMC/CHI) were estimated as MNPs were successively coated with polyelectrolytes. All the systems exhibited superparamagnetic-like behavior. Surprisingly, a stronger reduction was observed in the saturation magnetization of MNPs coated with synthetic polyelectrolytes (thinner shells) than in the system layered with natural polymers (thicker shells). Magnetization results suggest that synthetic polyelectrolytes adsorbed on the nanoparticle surface appear to have a stronger cooperativity than that of biopolymers, which could differently affect the interaction of spins located in the magnetically disordered regions in the nanoparticle surface.