One-step synthesis of Ru (bpy)(3) Cl-2-immobilized (bpy = 2,2'-bipyridine) silica nanoparticles (Ru-silica nanoparticles) for use in electrogenerated-chemiluminescence (ECL) detection is reported. Ru-silica nanoparticles are prepared by using the Stober method. Compared with free Ru(bpy)(3)Cl-2, Ru-silica nanoparticles are seen to exhibit a red-shift of the UV-vis absorbance peak and a longer fluorescence lifetime, which are attributed to the electrostatic interaction of Ru(bpy)(3)(2+) and silica. Because silica nanoparticles are used as immobilization matrices, the surfaces of Ru-silica nanoparticles are easily modified or functionalized via the assembly of other nanoparticles, such as Au. For ECL detection, Au-colloid-modified Ru-silica nanoparticles are immobilized on a 3-mercaptopropyl-trimethoxysilane-modified indium tin oxide electrode surface by Au-S interaction; the surface concentration of electroactive Ru(bpy)(3)Cl-2 is obviously higher than that in silica films. The modified electrode exhibits excellent ECL signals and gives a good linear range over 5 x 10(-7)-1.4 x 10(-3) M with a detection limit of 50 nm towards the tripropylamine (TPA) detection. Moreover, the electrode has better reproducibility and long-term stability for the determination of TPA than electrodes modified with pure Nafion, Nafion-silica, Nafion-TiO2, or sol-gel films containing Ru(bpy)(3)Cl-2. Immobilization of Ru(bpy)(3)Cl-2 on the electrode surface by this method is simple and easy, so it shows potential applications in the field of ECL analysis and detection.