Preparation And Characterization Of The Fluorescent Nano-TiO₂ Composites Microsphere

Owing to their cheap, nontoxic, as well as high thermal and chemical stability, TiO₂ nanomaterials have been widely applied in photocatalysis, fuel cells, sensors, etc. Compared with traditional TiO₂ microspheres, multifunctional TiO₂ hybrid microspheres can be finely designed and regulated to meet the demands of applications, which become one of the research focus. In this paper, fluorescent TiO₂ hybrid microspheres have been prepared by tipical sol-gel method, which will provide novel platform and challenge in the multifunctional fluorescent hybrid nanomaterials. Therefore, this paper will be carried out as the following three parts work around the fluorescent Ti O2 hybrid microspheres.In chapter 2, using the typical sol-gel method, the amorphous TiO₂ microspheres have been prepared and show good monodispersion. We discussed the effect of experiment conditions on the shape and size of TiO₂. Then, oil-souble carbon dots（CDs） were doped in the TiO₂ microspheres by similar sol-gel method. The hollow CDs/TiO₂ microsphere has a blue fluorescent emission of CDs. The CDs/TiO₂/Rhodamine B dual-emitting microspheres have been prepared by the regrow method. By adjusting of the amount of Rhodamine B, the dualemitting microspheres showed tunable fluorescence from blue to yellow under UV light illumination.In chapter 3, the surface of the CDs/TiO₂ microsphere was modified with amino group and then fluroscent CDs/TiO₂/AuNCs microsphere was prepared through carbodiimide-activated coupling reaction between GSH-AuNCs and amino-functionalized TiO₂ microspheres. The CDs/TiO₂/AuNCs microsphere shows characteristic dual-emitting property of CDs and AuNCs under a single excitation wavelength. Moreover, upon increasing the temperature, the intensity of red emission from the AuNCs continuously quenched, whereas that of blue emission from the CDs remained nearly constant. The different response results in a continuous fluorescence color change from red to purple that can be clearly observed by the naked eyes under UV light. The intensity ratio of the two emission wavelengths（I596/I436） showed a linear relationship with increasing temperature from 20 to 80 oC with small temperature resolution（⁰.5 °C）. Additionally, this nanosensor is successfully applied in 10 mM buffered saline（PBS） solution with physiological temperature ranging from 20 to 45 oC, which suggests as-prepared dualemitting microspheres have promising applications in vivo temperature sensing.In chapter 4, the CDs/TiO₂/CdSe hybrid microsphere has been prepared by coating CdSe quantum dots（QDs） on the surface of CDs doped TiO₂ microspheres which exhibits their corresponding dual emissions peaked at 436 and 596 nm, respectively, under a single excitation wavelength. The blue fluorescence of the CDs is insensitive to Fe³⁺, whereas the orange emission of CdSe QDs is functionalized to be selectively quenched by Fe³⁺. The intensity ratio of I436/I596 show good linear relationship with the concentration of Fe³⁺ in the range of 10-9 to 10-5 M. Moreover, 293 T cells are used as models to achieve a potential application as probe for monitoring Fe³⁺ in cells. Thus, these dual-emitting nanoprobe could work as an alternative to conventional fluorescence probes for biolabeling, sensing and other applications.