A methodology is described for the preparation of thermosensitive organic inorganic hybrid microgels with functional Fe3O4 nanoparticles as the crosslinker and N-isopropylacrylamide (NIPAm) as the monomer. Magnetic Fe3O4 nanoparticles were first prepared via a redox reaction in aqueous solution and then modified with 3-(trimethoxysilyl)propylmethacrylate (TMSPMA) via the silanization. The bonding of multiple TMSPMA monomers on the surface of Fe3O4 nanoparticles renders them as crosslinker. Surfactant-free emulsion polymerization (SFEP) of NIPAm was then carried out with the presence of TMSPMA-modified Fe3O4 nanoparticles at 70 degrees C in aqueous solution, leading to the formation of thermosensitive PNIPAm-Fe3O4 hybrid microgels crosslinked with Fe3O4 nanoparticles. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), thermogravimetric analysis (TGA), dynamic light scattering (DLS) and physical properties measurement system (PPMS) were then used to characterize the resultant hybrid microgels. The experimental results show that the PNIPAm-Fe3O4 hybrid microgels were spherical in shape with a large size distribution and the Fe3O4 nanoparticles were randomly distributed inside the microgels. The PNIPAm-Fe3O4 hybrid microgels were thermosensitive, exhibiting a reversible swelling and deswelling behavior as a function of temperature. The PNIPAm-Fe3O4 hybrid microgels also show superparamagnetic behavior at room temperature (300 K). (C) 2010 Elsevier Ltd. All rights reserved.