A sensitive electrogenerated chemiluminescence (ECL) detection of DNA hybridization, based on tris(2,2'-bipyridyl)ruthenium(II)-doped silica nanoparticles (Ru(bpy)(3)(2+) -doped SNPs) as DNA tags, is described. In this protocol, Ru(bPY)(3)(2+) -doped SNPs was used for DNA labeling with trimethoxysilylpropydiethylenetriamine(DETA) and glutaraldehyde as linking agents. The Ru(bPY)(3)(2+) -doped SNPs labeled DNA probe was hybridized with target DNA immobilized on the surface of polypyrrole (PPy) modified Pt electrode. The hybridization events were evaluated by ECL measurements and only the complementary sequence could form a double-stranded DNA (dsDNA) with DNA probe and give strong ECL signals. A three-base mismatch sequence and a non-complementary sequence had almost negligible responses. Due to the large number of Ru(bPY)(3)(2+) molecules inside SNPs, the assay allows detection at levels as low as 1.0 X 10(-13) Mol l(-1) of the target DNA. The intensity of ECL was linearly related to the concentration of the complementary sequence in the range of 2.0 x 10(-13) to 2.0 x 10(-9) mol l(-1). (c) 2006 Elsevier Ltd. All rights reserved.