Development of functionalized terbium fluorescent nanoparticles for antibody labeling and time-resolved fluoroimmunoassay application

Silica-based functionalized terbium fluorescent nanoparticles were prepared, characterized and developed as a fluorescence probe for antibody labeling and time-resolved fluoroimmunoassay. The nanoparticles were prepared in a water-in-oil (W/O) microemulsion containing a strongly fluorescent Tb3+ chelate, N,N,N1,N1-[2,6-bis(3′-aminomethyl-1′-pyrazolyl)phenylpyridine] tetrakis(acetate)-Tb3+ (BPTA-Tb3+), Triton X-100, octanol, and cyclohexane by controlling copolymerization of tetraethyl orthosilicate (TEOS) and 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AEPS) with ammonia water. The characterizations by transmission electron microscopy and fluorometric methods show that the nanoparticles are spherical and uniform in size, 45 ± 3 nm in diameter, strongly fluorescent with fluorescence quantum yield of 10% and a long fluorescence lifetime of 2.0 ms. The amino groups directly introduced to the nanoparticle’s surface by using AEPS in the preparation made the surface modification and bioconjugation of the nanoparticles easier. The nanoparticle-labeled anti-human α-fetoprotein antibody was prepared and used for time-resolved fluoroimmunoassay of α-fetoprotein (AFP) in human serum samples. The assay response is linear from 0.10 ng ml−1 to about 100 ng ml−1 with the detection limit of 0.10 ng ml−1. The coefficient variations (CVs) of the method are less than 9.0%, and the recoveries are in the range of 84–98% for human serum sample measurements.