Ag nanoparticle-catalyzed chemiluminescent reaction between luminol and hydrogen peroxide

Ag colloid was found to enhance intensely the chemiluminescence (CL) from the reaction between luminol and hydrogen peroxide. Ag nanoparticles exhibited the better CL catalysis activity than gold and platinum nanoparticles. The superoxide anion scavenger nitro blue tetrazolium and superoxide dismutase was added to the hydrogen peroxide-Ag colloid and the luminol-hydrogen peroxide-Ag colloid systems, respectively, showing that the decomposition of hydrogen peroxide by catalysis of silver nanoparticles formed superoxide anion and superoxide anion was involved in luminol-hydrogen peroxide-Ag colloid CL reaction. The Ag nanoparticle-enhanced CL was ascribed to that Ag nanoparticles could catalyze the decomposition of H2O2 to produce some reactive intermediates such as hydroxyl radical, superoxide anion. Hydroxyl radical reacted with luminol to form luminol radical and diazaquinone, followed by the reaction with superoxide anion or monodissociated hydrogen peroxide, giving rising to light emission. Halide ions (X-) were found to quench the CL in the following order: I- > Br- > Cl-, due to the formation of AgX shell on Ag nanoparticles surface which poisoned the Ag catalyst. An obvious turning point was observed in the curve of CL intensity versus iodine ion concentration, which corresponded to the I- concentration needed for mono-layer saturation adsorption on the Ag nanoparticles. A chemical adsorption model for iodine ions on the surface of Ag colloids has been proposed. Among 20 natural amino acids, cysteine, histidine, methionine, tyrosine and tryptophan were found to inhibit the CL due to their adsorption on the Ag nanoparticles and their competitive consumption for the reactive intermediates. The most intense inhibition of cysteine may be of potential for selective determination of cysteine. (C) 2007 Elsevier B.V. All rights reserved.