| Magnetic fluorescent multifunctional polymer beads have been attracted great interest in application of biomedical field not only due to their advantages of big surface area, size-controlled, separated facility and ease to be functionalized on the surface, but also performance unique superparamagnetization and excellent optical properties. In particular, these functional beads have broad application prospect in encoding, cell separation, resonance imaging, drug screening and targeting, disease detection and diagnosis, etc.The preparation of monodisperse magnetic fluorescent multifunctional polystyrene beads and the effect of different factors and conditions on microsphere structure, performance and parameter were investigated in detail in this work. Bio-immunoassay and clinical diagnosis were operated on bead surface as a primary application. Firstly, two-step swelling seed polymerization was adopted to synthesize carboxylic beads in size of 1-15μm with polystyrene particles by dispersion polymerization in size of 1-3μm as seed latex. The schematics and reaction dynamics of dispersion polymerization and seed polymerization were described and the effects of conditions on size, morphology and properties of seed particles and target beads were discussed. Bead adsorption, reaction capacity and carboxylic activity were evaluated by BCA protein adsorption and ELISA assay. Secondly, an efficiently modified method combined conventional swelling method with high-temperature swelling method was applied to prepare high-stable multifunctional MNPs-QD-encoded polystyrene beads simultaneously with large encoding capacity and fast separation. Subsequently, fluorescent and magnetic performances were investaged in detail and the stability of multifunctional beads in organic solvent, buffers with different pH. The long-time stability in PBS buffer as an important characterization was used to perform that functional bead can store and apply for a long time, such as 6 months.The regular morphology, uniform size can be observed from SEM images and beads with varied size can be completely separated from each other in flow cytomic data, so that encoding by bead size can be realized. The fact that carboxyl groups were successfully integrated onto bead surface can be obtained from NMR and FTIR spectra and the concentration is 0.4mmol/g by conductometric titration. QDs were packed into bead network and well-distributed seeing from laser scanning confocal microscope; meanwhile, magnetic performance was excellent getting from vibration magnetometer and separation photos. In this work, the results demonstrate that encapsulating QDs into pre-prepared MNPs-beads is the best sequence, which keeps high brightness and fast separation. The MNPs-QD-encoded microcarriers designed by our proposed method exhibit excellent performance for magnetic manipulation and optical encoding; what is more, they also have strong physical and chemical stabilities. Compared with beads prepared via conventional swelling method, the leakage of nanoparticles from the designed MNPs-QD-encoded PSEMBs induced by organic solvents (cyclohexane) is less than 6 % and fluorescence intensity of MNPs- QDs-encoded PSEMBs fluctuates more slightly in a wide range of pH 4-12 buffers; meanwhile, fluorescence intensity kept the low level less than 40% for 6 months in PBS buffer. In addition, immunoassay performance for human IgG detections indicates that carboxyl groups on fluorescence microsphere surface facilitate efficient attachment of biomacromolecule and therefore they can be further applied to fast separation and multiplexed biomolecular assays.The results of research can provide important theoretical and experimental basis for the bead-encoding development of liquid biochip, and has broad application prospects in the field of testing biometrics. |
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