Monodisperse superparamagnetic polymer composite microspheres with high magnetite content were prepared by seed emulsion co-polymerization.In this system

0.7~0.8 m Fe3O4 magnetic aggregation droplets which were consisting of Fe3O4 nanoparticles with an average particle size of 10 nm were severed as seeds and droplets of styrene and divinylbenzene were used as monomers to swell the seeds before the polymerization.The influence of the swelling time on the morphology and magnetite nanoparticles content of the composite microspheres was also investigated.The obtained microspheres with diameter of 0.7~1.0 m were superparamagnetic and with the magnetite nanoparticles content of 29 wt%~57 wt%

which were extensively characterized by transmission electron microscopy (TEM)

thermogravimetric analysis (TGA)

Fourier transform infrared spectrometer (FTIR) and vibrating sample magnetometer (VSM).By adjusting the swelling time

a series of microspheres with different morphologies were also obtained and characterized.The result indicated that the degree of phase separation of the obtained microspheres increased when the swelling time decreased.On the other hand

the carboxyl group was introduced onto the surface of the above magnetic microspheres via a two-step seed emulsion co-polymerization using acrylic acid as a functional polymeric monomer.After that

the as synthesized superparamagnetic polymer composite microspheres with carboxyl groups (the density of carboxyl group was about 0.92 mmol/g beads) were conjugated with the bio-molecules (hCG was used as a model detection of bio-molecules in this study) and then applied into the chemiluminescence immunoassay.The obtained well performance showed the feasibility of the microsphere to be used as a potential and promising material for bio-detection.