Hot electron injection into aqueous electrolyte solutions from metal/insulator/metal/electrolyte and metal/insulator/electrolyte tunnel junctions is considered and the possibility of an electrochemical generation of hydrated electrons is discussed. The hot electron-induced UV electrochemiluminescence of (9-Ñuorenyl)methanol was used to demonstrate the presence of highly energetic transient species in aqueous solution at several metal/insulator/electrolyte hot electron tunnel emitters. These transient species cannot be produced electrochemically in fully aqueous solutions at any active metal electrodes. A detailed mechanism for the present electrochemiluminescence is suggested.

No abstract

No abstract

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.

Ruthenium(II) tris-(2,2‘-bipyridine) chelate exhibits strong electrogenerated chemiluminescence during cathodic pulse polarization of oxide-covered aluminum electrodes in aqueous solutions. The present method is based on a tunnel emission of hot electrons into an aqueous electrolyte solution. The method allows the detection of ruthenium(II) tris-(2,2‘-bipyridine) and its derivatives below nanomolar concentration levels and yields linear log−log calibration plots spanning several orders of magnitude of concentration. This method allows simultaneous excitation of derivatives of ruthenium(II) tris-(2,2‘-bipyridine) and Tb(III)-chelates. The former label compounds have a luminescence lifetime of the order of microseconds, while the latter compounds generally have a luminescence lifetime of around 2 ms. Thus, the combined use of these labels easily provides the basis for two-parameter bioaffinity assays by either using wavelength or time discrimination or their combination.

No abstract

Hot electron injection into aqueous electrolyte solution was studied with electrochemiluminescence and electron paramagnetic resonance (EPR) methods. Both methods provide further indirect support for the previously proposed hot electron emission mechanisms from thin insulating filmcoated electrodes to aqueous electrolyte solutions. The results do not rule out the possibility of hydrated electron being as a cathodic intermediate in the reduction reactions at cathodically pulse-polarized thin insulating film-coated electrodes. However, no direct evidence for electrochemical generation of hydrated electrons could be obtained with EPR, only spin-trapping experiments could give information about the primary cathodic steps. +IntroductionIt has been shown earlier that very different types of luminophores emitting in the visible range can be electrochemically excited during cathodic pulsepolarization of oxide-covered aluminium 1 and n-silicon 2 electrodes. In addition, it was later shown that (9-fluorenyl)methanol (FMOC-OH), emitting strong electrogenerated chemiluminescence (ECL) in the UV range, can be cathodically excited at thin insulating film-coated electrodes such as at oxide-covered aluminium, magnesium and n-silicon electrodes. 3 It was also shown 3 that strong ECL of FMOC-OH could only be produced in the direct field-assisted tunneling regime, 4 while in the Fowler-Nordheim (FN) tunneling regime 4 where the electrons are mainly transferred to the solution from the bottom of the conduction band of the oxide, the ECL intensity decreased exponentially as a function of the oxide film thickness. 3The tunnel-emitted hot electrons and hydroxyl radicals, 2,3,5,6 or in the presence of peroxydisulfate ions, hot electrons and sulfate radicals 2,3 have been proposed to be the primary mediating radicals responsible for the excitation reactions of luminophores in aqueous solution and in electroluminoimmunoassays. 7The aim of this work was to study the other types of luminophores having differing photophysics and redox chemistry would show the analogous behavior when changing from the direct field-assisted tunneling regime to FN tunneling regime. We wanted to study also, whether toluene or phenol could be used instead of FMOC-OH as more simple aromatic model compounds exhibiting high energy ECL in the aqueous medium. Efforts were also made to detect directly the hot or hydrated electrons, and secondary radicals formed from luminophores and coreactants in the cell built in an EPR measurement resonator. Spin-trapping experiments were also conducted.

No abstract