Dual-lanthanide-chelated silica nanoparticles as labels for highly sensitive time-resolved fluorometry

We have synthesized dual-lanthanide-chelated silica nanoparticles for potential use as labels in bioanalysis. A universal ligand 2,9-bis[N,N-bis(carboxymethyl)aminomethyl]-1,10-phenanthroline that could bind both Eu(III) and Tb(III) was covalently linked with 3-aminopropyl(triethoxy) silane to form silica nanoparticles in the presence of precisely controlled ratios of Eu(III)/Tb(III). The nanoparticles thus prepared could have specified ratios of luminescence intensities at two well-resolved emissions under a single-wavelength excitation. After comprehensive characterization with respect to their fluorescence lifetime, photostability, thermostability, and chelate leakage, a practical use of these nanoparticles was evaluated in a time-resolved immunofluorometric assay of human hepatitis B surface antigen. The results showed much increased sensitivity and quantification ranges than the enzyme-linked immunosorbent assay, demonstrating the suitability and advantages of these nanoparticles for bioassays.