Preparation and Time-Resolved Fluorometric Application of Luminescent Europium Nanoparticles

Novel silica-coated luminescent europium (SCLE) nanoparticles have been prepared by copolymerization of tetraethyl orthosilicate and 3-aminopropyl(triethoxy)silane with ammonium hydroxide in a water-in-oil microemulsion containing a luminescent Eu3+ chelate, Triton X-100, n-octanol, and cyclohexane. The nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, and UV−vis and luminescence spectra. The results show that the nanoparticles are spherical and uniform in size, 50 ± 5 nm in diameter, and have high photostability and long luminescence lifetime (770 μs). Because primary amino groups have been directly introduced to the nanoparticle's surface by using 3-aminopropyl(triethoxyl)silane in nanoparticle preparation, the surface modification and bioconjugation of the nanoparticles are easier and reproducible. The nanoparticles were used for streptavidin (SA) labeling, and the nanoparticle-labeled streptavidin was successfully used in time-resolved fluoroimmunoassay of human α-fetoprotein. The results reveal that the new nanoparticles are favorable for use as a new type of luminescence probe for highly sensitive time-resolved luminescence bioassay.