Cathodic Electrogenerated Chemiluminescence of Luminol at Disposable Oxide-Covered Aluminum Electrodes

Luminol exhibits strong electrogenerated chemiluminescence during cathodic pulse polarization of oxide-covered aluminum electrodes in aqueous solution. This electrogenerated chemiluminescence can be enhanced by the presence of dissolved oxygen or by the addition of other coreactants such as hydrogen peroxide, peroxydisulfate, or peroxydiphosphate ions. However, luminol detection is most sensitive in the presence of azide ions, which not only enhance the electrogenerated chemiluminescence intensity but also decrease the intrinsic electroluminescence of the thin aluminum oxide film on the electrodes mainly producing the blank emission. The present method is based on tunnel emission of hot electrons into an aqueous electrolyte solution and allows the detection of luminol, isoluminol, and its derivatives below nanomolar concentration levels. The linear logarithmic calibration range covers several orders of magnitude of concentration of luminol or N-(6-aminohexyl)-N-ethylisoluminol. Therefore, the above-mentioned labeling substances can be used as one of several available alternatives of simultaneous markers in multiparameter bioaffinity assays at disposable oxide-covered aluminum electrodes. The main advantage of the present electrochemiluminescence generation method is that luminescent compounds having very different photophysics and chemistry can be simultaneously excited, thus providing good possibilities for internal standardization and multiparameter bioaffinity assays.