Novel fluorescent europium chelate-doped silica nanoparticles: preparation, characterization and time-resolved fluorometric application

Novel fluorescent europium(III) chelate-doped silica nanoparticles were prepared and characterized as a new type of fluorescence probe for quantitative bioassay. The preparation was carried Out in a water-in-oil (w/o) microemulsion consisting of a strongly fluorescent Eu3+ chelate, 4,4'-bis(1",1",1",2",2",3",3"-heptafluoro-4",6"-hexanedion-6"-yl)-o-terphenyl-Eu3+ (BHHT-EU3+), surfactant (Triton X-100), co-surfactant (n-hexanol, n-heptanol or n-octanol), aqueous phase (H2O or D2O) and oil phase (cyclohexane) by controlling the hydrolysis of tetraethylorthosilicate (TEOS). The effects of different co-surfactants and aqueous phases on the size and fluorescence lifetime of the nanoparticles were investigated. The results reveal that the size of the nanoparticles is decreased with a change of co-surfactants from n-hexanol to n-octanol, and the fluorescence lifetime of the nanoparticles is increased with a change of aqueous phase from H2O to D2O. A new method was established for the surface modification and bioconjugation of the nanoparticles. Nanoparticle-labeled streptavidin (SA) was used for the time-resolved fluoroimmunoassay of human hepatitis B surface antigen (HBsAg). The result shows that the new fluorescent europium(III) chelate-doped silica nanoparticles are suitable to be used as a fluorescence probe for highly sensitive bioassays.