The Preparation And Biomedical Applications Of Monodisperse Carboxylic Polystyrene Microspheres

There is extensive research and using value of monodisperse micron-sized polystyrene microspheres in immunological technique and early diagnosis of diseases. It is attributed to many advantages of the microspheres such as good spherical shape, uniform size, high surface reaction capability, and easily to be functionalized. The preparation of high-performance encoded beads play a critical role in the field of suspension array biochip for rapid and multiplex detection.In this work, the preparation of monodisperse functionalized polystyrene microspheres, encoding methods and their applications in immunological technique were investigated. Firstly, the 2μm polystyrene seeds were synthesized by dispersion polymerization. And carboxylated polystyrene microspheres with the diameter in the range of 5-15μm were prepared via seed polymerization. The mechanism of seed polymerization and the copolymerization feasibility of styrene with methacrylic acid (MAA) were studied. The parameters influencing the diameter and morphology of microspheres, including the monomer swelling time, the content of styrene and MAA, were investigated. The reactivity of carboxyl group on the surface of microspheres was confirmed by enzyme linked immunosorbent assay (ELISA). Secondly, for producing porous polystyrene microspheres, toluene as the porogen was added into the system during the monomer swelling stage of seed polymerization. The effect of the toluene content and the crosslinking degree on the size and distribution of pore on the microsphere surface were investigated. Quantum Dot-encoded fluorescent microspheres were successfully obtained by tagging quantum dots (QDs) with different fluorescence emission peaks into porous microspheres. The fluorescent properties of the porous quantum dot-encoded fluorescent microspheres were characterized. The porous quantum dot-encoded fluorescent microspheres were used in immunoreactions and their fluorescence spectra were obtained by optical fiber optic spectrograph.The monodisperse and spherical microspheres was observed in the scanning electronic microscope (SEM) photographs. In flow cytometry analysis, the microspheres with various sizes can be completely separated into different groups, which show the diameter-encoded method can be validly employed in the multiplexing detection systems. The results of FTIR and 1HNMR indicated that the MAA monomer was successfully copolymerized to the microspheres. The content of carboxyl group on the microsphere surface was 0.3mmol/g via conductometric titration. The high reactivity of carboxyl group on the surface of microspheres was well established by immunoreactions. The fluorescence photographs and spectrums showed that the quantum dot-encoded fluorescent microspheres were effectively encoded using QDs with different emission wavelengths. The fluorescent intensity distribution of quantum dot-encoded fluorescent microspheres was characterized by the laser confocal fluorescence microscopy. The results showed that the QDs permeated into the porous microspheres effectively via the interior pores, offering a more homogeneous interior fluorescent intensity than the non-porous ones. The immunoreactions showed that the porous quantum dot-encoded fluorescent microspheres can be sensitized by antigen (human IgG) stably and capture the antibody specifically (QDs labled goat-anti-human IgG).This work is beneficial to fabrication of polymer beads for suspension array biochip, and this robust study can be further utilized to the field of immunological technique and early diagnosis of diseases.