# These two authors contributed equally to this paper.
## 2 Results and Discussion  
### Preparation and surface modification of the SPMP microbeads  
The magnetic polymer microspheres obtained from conventional suspension polymerization methods were in the size of several hundred micrometers. We developed a novel modified suspension polymerization method for the production of superparamagnetic polymer microspheres with micron size, which have narrow size distribution and high magnetite contents [12]. As seen in Scheme 1, magnetic fluid was prepared by a conventional coprecipitation method, then oleic acid was added dropwise into the suspension while heating. After the excess oleic acid was removed, the magnetic precipitate was redispersed in hexane to form magnetic fluid. The obtained Fe\({}_{3}\)O\({}_{4}\) fluid and benzoyl peroxide (BPO) were dispersed in a mixture of methacrylate (MA) and divinyl benzene (DVB), and agitated until Fe\({}_{3}\)O\({}_{4}\) was dissolved completely. The mixture was then transferred into a beaker containing polyvinyl alcohol (PVA). With rapid agitation, the mixture temperature was increased to reaction temperature under the protection of nitrogen and kept. The resulting magnetic microspheres were thoroughly washed to remove the excess monomer. After being agitated in methylformamide (DMF) and ethylenediamine (EDA), the ester groups on the poly(MA-DVB) microspheres were converted into amino groups, and the resulting microspheres were denoted as poly(MA-DVB)-NH\({}_{2}\). To facilitate the covalent attachment of antibody, the amino groups on the surface of magnetic poly(MMA-DVB)-NH\({}_{2}\) were transferred to aldehyde groups by the glutaraldehyde method. The adding of the DVB as crosslink made the polymer structure change from linear type to three-dimensional crosslink type, just as what we could see from the Scheme 1, which increased greatly the mechanic strength and the stability of SPMP. The detailed numbers of MMA and DVB in the polymer macromolecules relied on their molecular ratio. [PERSON] [21] thought that this kind of cross-linking was necessary. Because a simple noncovalent linkage between the iron oxide cores and the polymeric chain were not sufficient to achieve a permanent linkage. Instead, a dynamic exchange between the polymeric chains and other competing molecules possessing a -COOH group such as peptides and amino acids in the biological systems could lead to the dissociation of the polymeric chains from the core surfaces. The loss of the coating material and its terminal functionalities could demolish the biospecificity of these materials. [PERSON] [10] also found that this cross-linkage was particularly well suited to protect and functionalize materials such as Fe \({}_{3}\)O\({}_{4}\), \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) for which strongly binding surface ligands were not readily available, for it could fix the nanostructures topologically and these structures were stable to further synthetic transformations of surface functional groups. Poly(MA-DVB), the SPMP microbeads synthesized by the modified suspension polymerization method, possessed the perfect sphere configuration, shown in Scheme.2(a). Most of these spheres were about 3 \(\upmu\)m in diameters, but there still were a few below 2.5 \(\upmu\)m due to the unhomogeneous of the microemulsion diameter variating in 0.5-3 \(\upmu\)m. Scheme 2(b) was the TEM picture of a single microbead. From the picture, we could see that the surface of the magnetic Poly(MA-DVB) microbeads was not so smooth, and there were full of small protuberances, and some tiny block in the outside of the sphere. These protuberances and blocks would increase the surface area to be ammonolysis by EDA, and provide amino groups and aldehyde groups at high density [22]. Such a procedure to synthesize the SPMP microbeads often bring several advantages to these magnetic beads. First, the integration and fix of many tiny magnetic cores guarantee the superparamagnetism andmagnetophoresis ability due to the large amount of magnetic material percentage.