Lucigenin chemiluminescence induced by noble metal nanoparticles in the presence of adsorbates

It was found that noble metal nanoparticles including Ag, Au, and Pt nanoparticles in the presence of adsorbates such as iodide ion, cysteine, mercaptoacetic acid, mercaptopropionic acid, and thiourea could reduce lucigenin (bis-N-methylacridinium) to produce chemiluminescence (CL). Lucigenin-Ag-KI system was chosen as a model to study the CL process. Absorption spectra and X-ray photoelectron spectra showed that when the Ag colloid was mixed with KI, Ag nanoparticles were covered by adsorbed iodide ions. X-ray diffraction patterns and fluorescence spectra indicated that Ag nanoparticles were oxidized to AgI and lucigenin was converted to N-methylacridone in the CL reaction. The addition of superoxide dismutase could inhibit the CL. According to Nernst's equation, the presence of iodide ions decreased the oxidation potential of Ag nanoparticles. As a result, lucigenin was rapidly reduced by Ag nanoparticle to a monocation radical, which reacted with oxygen to generate a superoxide anion; then the superoxide anion reacted with the monocation radical to produce CL. Other adsorbates such as cysteine, mercaptoacetic acid, mercaptopropionic acid, and thiourea that could decrease the oxidation potential of Ag nanoparticles could also induce the CL reaction.