Mika Helin

Electrochemiluminoimmunoassay of hTSH at disposable oxide-coated n-silicon electrodes

Abstract Cathodic pulse polarisation of thin insulating film-coated electrodes enables the generation of electrochemiluminescence (ECL) by tunnel emission of hot electrons from the Fermi level of the conductor material of the conductor–insulator–aqueous electrolyte solution junction to the solutes at the vicinity of the electrode surface and probably also to the conduction band of water. The latter process can generate hydrated electrons as strongly reducing slightly longer-lived cathodic intermediate s , which are known to be able to induce chemiluminescence (CL) of various types of luminophores having very different photophysical and chemical properties. The generation of the above-mentioned cathodic primary species provides good possibilities to use many types of luminophores as label molecules in sensitive immuno and DNA-probing assays. This paper introduces an electrochemiluminoimmunoassay (ECLIA) for human thyroid stimulating hormone (hTSH) at oxide-coated n-silicon electrodes and demonstrates the suitability of silicon electrodes covered with thermally grown silicon dioxide film as disposable working electrodes (WEs) in sensitive time-resolved ECL (tr-ECL) measurements in aqueous solution. The label chelate can be detected almost down to picomolar level and the calibration curve of the chelate covers more than five orders of magnitude of chelate concentration. Also the calibration curve of the immunometric hTSH assay was found to be linear over a wide range of hTSH concentration, the detection limit of the hormone being below 1 mU l −1 (4 pmol l −1 ).

Hot electron-induced electrogenerated luminescence of Tl(I) at disposable oxide-covered aluminum electrodes

Abstract Cathodic pulse polarisation of oxide-covered aluminum electrodes in Tl(I) solutions induce strong Tl(I)-specific electrogenerated luminescence (EL). It is mainly regarded as electrochemiluminescence, induced by one-electron oxidation of cathodically produced thallium atoms in the close vicinity of the electrode surface, but solid state electroluminescence is also produced, especially, with thicker oxide films. Depending on the EL system applied, the oxidant in response of the excitation event is either a cathodically produced hydroxyl or sulfate radical, or an F + -centre of the thin oxide film, and the source of short-lived thallium atom colloids is a reduction of Tl(I) ions by tunnel-emitted hot electrons and/or cathodically generated hydrated electrons. The present method allows the detection of Tl(I) ions below nanomolar concentration level and provides linear log-log calibration graphs spanning several orders of magnitude of concentration of Tl(I).

Time-Resolved Detection of Hot Electron-Induced Electrochemiluminescence of Fluorescein in Aqueous Solution

Strong electrogenerated chemiluminescence (ECL) of fluorescein is generated during cathodic pulse polarization of oxide-covered aluminum electrodes and the resulting decay of emission is so sluggish that time-resolved detection of fluorescein is feasible. The present ECL in aqueous solution is based on the tunnel emission of hot electrons into the aqueous electrolyte solution, which probably results in the generation of hydrated electrons and hydroxyl radicals acting as redox mediators. The successive one-electron redox steps with the primary radicals result in fluorescein in its lowest excited singlet state. The method allows the detection of fluorescein (or its derivatives containing usable linking groups to biomolecules) over several orders of magnitude of concentration with detection limits well below nanomolar concentration level. The detection limits can still be lowered, e.g., by addition of azide or bromide ions as coreactants. The results suggest that the derivatives of fluorescein, such as fluorescein isothiocyanate (FITC), can be detected by time-resolved measurements and thus be efficiently used as electrochemiluminescent labels in bioaffinity assays.