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

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 intermediates, 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).