Synthesis And Application Of Silica-based Composite Microspheres

As a new type of materials, functional nanocomposites have attracted moreattention. Especially, composite nanoparticles with core-shell structures have shownto be superior to single component nanoparticles through the combination ofappropriate functional components and have shown broad prospects for applicationsin medical imaging, molecular diagnosis, fluorescent immunoassay, biomaterialseparation and so on. Due to the unique optical properties and ease of surfacemodifications of SiO₂, composite materials modified with SiO₂, can not only maintaintheir primary properties, but also improve their dispersion, stability andbiocompatibility, and provide a good carrier for their functionalization.Nanocomposite materials have now become a hot topic in scientific research.This thesis reporte the use of silica as the shell for the synthesis of a series ofcore-shell fluorescent particles （FPs） and magnetic-fluorescent bifunctionalparticles（MN-QDs）. Application of the FPs of SiO₂for the development of latentfingerprints was performed. This dissertation consists of the following three parts.（1） Fluorescent silica particles （FSPs） were prepared by co-hydrolyzation ofTEOS and PTOS with fluorescent dye-Rhodamine B （RB）. This part focused on theeffects of the components in the system on the doping efficiency of RB, diameter,fluorescence property and monodispersion property of the FSPs. As the quantity ofaqueous ammonia increases，the diameter of particles increases apparently andmono-dispersity of size-distribution improves as well. FSPs with narrowsize-distribution and average diameter of630nm were prepared using3mL ofaqueous ammoniain in30mL ethanol and5mL water mixture. Increasing the amountof PTOS and TEOS is helpful for improving the doping efficiency of RB, but has adverse effect on the mono-dispersity of size-distribution. It was found that the FSPsshowed best morphology and mono-dispersity when0.125mmol of RB and1.0mL ofPTOS was used in30mL ethanol and5mL water mixture. RBS, synthesized throughcondensation reaction between RB and3-aminopropyltriethoxysilane （APTS）, wascovalently incorporated into the silica nanoparticles. The optimal molar ratio of APTSand RB and the amount of RBS were found to be around2:1and1.5mmol,respectively, for the best performance for spheres of RBS.（2） To improve their dispersibility, Fe₃O₄particles were modified with sodiumcitrate. Microspheres with core–shell structure （denoted as Fe₃O₄/SiO₂） were preparedand the thickness of silica coating can be altered by varying the amount oftetraethoxysilane （TEOS） loaded. Fe₃O₄/SiO₂microspheres with a silica coating layerof6nm,15nm,20nm and31nm in thickness were obtained. According to the results,the optimal conditions for the synthesis of Fe₃O₄/SiO₂were concluded.Functionalized Fe₃O₄/SiO₂with APTMS modification was prepared for the next steps.Fe₃O₄and Fe₃O₄/SiO₂were characterized by XRD, FT–IR and PPMS.（3） Using the above Fe₃O₄/SiO₂–APTMS, MN-QDs were prepared in three steps.First, QDs attached to APTS-functionalized Fe₃O₄/SiO₂by chemical interactionbetween the QDs and the–N2H in tetrahydrofuran （THF）. The MN-QDs microsphereshave the best monodispersion with mixing5mg of QDs and10mg Fe₃O₄/SiO₂/NH2-in40mL THF. Second, encapsulation of MN-QDs were performed using thioglycolicacid, polyvinyl pyrrolidone （PVP）, and3-Mercaptopropyltriethoxysilane （MPTES）,the amount of MPTES added was optimized. The MN-QDs showed best fluorescenceintensity and dispersion with adding120μL of MPTES in30mL isopropylalcohol.Third, in order to improve their chemical stability, the MN-QDs were finallycovered with an outer shell of silica. It was shown that a shell of5nm can be grownover the MPTES-modified MN-QDs by adding appropriated amount of TEOS. Theas-prepared MN-QDs showed bright fluorescence and good mono-dispersity.