Silica nanoparticles (SiNPs) with an average diameter of 25 nm were prepared by a one-pot method that involves the formation of a silica core that is subsequently covered with a shell functionalized with either azido groups or alkyne groups for use in copper(I)-catalyzed click reactions. Respective triethoxysilane reagents are presented The SiNPs were (a) rendered fluorescent by click conjugation to fluorophores of various colors, and (b) made bioconjugatable by Introducing maleimide groups (that covalently bind thiols) and biotin (a widely used bioaffinity reagent that binds streptavidin) Particles were characterized by transmission electron microscopy, infrared spectroscopy, fluorescence, and light scattering. The fluorescently labeled SiNPs carrying maleimido groups were conjugated to the thiol group of bovine serum albumin (BSA) labeled with a fluorophore. and fluorescence resonance energy transfer was shown to occur between the labeled SiNPs and the labeled BSA This is considered to represent a new approach towards nanoparticle-based fluorescent bioassays. (C) 2010 Elsevier B.V All rights reserved