A upconversion nanocrystal of NaYF₄:Yb/Tm was synthesized successfully by two different methods of solvothermal and hydrothermal, respectively. The properties of the products were characterized and compared. The results showed that the nanocrystal prepared by hydrothermal method exhibited uniform hexagonal phase and large size, while the nanocrystal prepared by solvothermal method displayed high upconversion luminescence (UCL) and small size. The UCL intensity of the nanocrystal from solvothermal method was higher than that of hydrothermal method. This is the first time to systematically compare the performances of the upconversion nanocrystal prepared by solvothermal and hydrothermal methods, which provides some new insight into the preparation of upconversion nanomaterials with intense UCL and controllable morphology.

Nanoparticle labes conjuaged with biomolecules have been used in a variety of different assay application. We investigated the possibility of using europium(Ⅲ) chated-doped silica nanoparticle conjugated with streptavidin (SA) to detect mouse IgG by time-resolved fluorescence immunoassay (TRFIA). Results demonstrate that the nanoparticle is a novel kind of superior fluourscent probe which could be effectively applied in time-resolved fluorescent immunoassay with high detective sensitivity. In the present study, the lowest detection limit of mouse IgG is 34 pg mL^-1.

A novel type of amino functionalized core-shell Ru(bpy)₃-doped silica nanoparticles was synthesized using a simple and effective approach of reverse microemulsion. The nanoparticles were characterized by transmission electron microscope, fluorescence spectra, UV-Vis spectroscopy and tests of photostability and dye molecular leakage. It was found that the nanoparticles exhibit excellent fluorescent properties such as extremely bright, highly photostable and chemicalstable. Furthermore, the nanoparticles utilized as a fluorescent marker applying in fluorescent immunoassay of mouse IgG were studied and desired results were obtained.

A new ligand of 4,7-diphenyl-1,10-phenanthroline-2,9-dicarboxylic acid (DPPDA) and Eu³⁺chelate compound of this ligand were prepared. Then DPPDA-Eu³⁺ doped silica fluorescent nanoparticles of DPPDA-Eu³⁺/SiO₂ with primary amino groups on their surface were developed using a water-in-oil (W/O) microemulsion technique. Characterizations by transmission electron microscopy, fluorescent spectra, fluorescent molecules leaking experiments and photostable experiments show that the nanoparticles are spherical, monodisperse, and uniform in size (80±8 nm in diameter). The nanoparticles have high fluorescent signal and high photostability. When the nanoparticles were dispersed in aqueous solution with continuously ultrasound for 4 h, no obvious leakage of fluorescent molecules were observed. As a novel fluorescent probe, the nanoparticles are expected to be applied in highly sensitive bioassays systems such as time-resolved fluorescence immunoassay, biosensor and biochip.

A novel type of amino functionalized core-shell fluorescein isothiocyanate-doped silica nanoparticles was synthesized using a simple and effective approach of reverse microemulsion. Isothiocyanate coupled with a silane coupling agent, 3-aminopropyltrimethoxysilane, was incorporated into silica sphere and the dye molecules were bound with silica sphere through hydrolysis and polymerization of tetraethoxysilane and 3-aminopropyl-trimethoxysilane. With the covalent binding between the dye molecules and silica sphere, the leakage of the dye was avoided. With amino groups on the surface, the nanoparticles can be directly conjugated with biological molecules with no need of surface modification. The nanoparticles were pH sensitive, highly fluorescent and highly photostable. The pH response range and pH responsive linear range were 2.8~8.5 and 4.6~8.0, respectively. More interestedly, the nanoparticles could be phagocytosed by murine neural stem cell and could be applied to detect pH value for single alive cell.