We synthesized ZnO-nanoparticle quantum dots (QDs) as a fluorescent probe for biological applications. Highly luminescent silica-coated ZnO-nanoparticle QDs dispersed in an aqueous medium were synthesized using the sol-gel process. The ZnO-nanoparticle QDs were coated with silica to improve the water stability of the ZnO nanoparticles. NH2 groups were introduced on the surface of the silica-coated ZnO-nanoparticle QDs first by the addition of 3-aminopropyltrimethoxysilane and then by biotinylation with sulfosuccinimidyl-6-(biotin-amido) hexanoate (sulfo-NHS-LC-bioton). We demonstrated that avidin-immobilized agarose beads were tagged by the silica-coated ZnO-nanoparticle QDs with biotin by the selective avidin-biotin interaction, furnishing a fluorescent image upon excitation with UV light. Furthermore, use of the silica-coated ZnO-nanoparticle QDs with biotin in cell-labeling applications was attempted, and attachment of the silica-coated ZnO-nanoparticle QDs with biotin to nerve cells and actin filaments was achieved. (C) 2013 Elsevier Inc. All rights reserved.