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.

Generation of free radicals and electrochemiluminescence from simple aromatic molecules in aqueous solutions.

Oxide-covered aluminium electrodes were used to demonstrate that aromatic compounds, such as the simple derivatives of benzene, can be electrochemically excited at cathodically pulse-polarized conductor/insulator/electrolyte (C/I/E) tunnel junction electrodes (e.g. oxide-covered aluminium electrodes). The primary cathodic process at these electrodes was a tunnel emission of hot electrons into an aqueous electrolyte solution. Fluorescence (FL) and electrochemiluminescence (ECL) spectra were compared and the dependence of the electrochemiluminescence on the concentrations of benzene, toluene, phenol, p-cresol and aniline were measured and detailed mechanisms for the present electrochemiluminescence are proposed.

Rapid electrochemiluminoimmunoassay of human C-reactive protein at planar disposable oxide-coated silicon electrodes.

Electrochemiluminescence (ECL) of aromatic Tb(III) chelates at thin insulating film-coated electrodes provides a means for extremely sensitive detection of Tb(III) chelates and also of biologically interesting compounds if these chelates are used as labels in bioaffinity assays. The suitability of silicon electrodes coated with thermally grown silicon dioxide film as disposable working electrodes in sensitive time-resolved ECL measurements is demonstrated, and a rapid electrochemiluminoimmunoassay (ECLIA) of human C-reactive protein (hCRP) is described. Tb(III) chelate labels can be detected almost down to picomolar level, and the calibration curve of these labels covers more than 6 orders of magnitude of chelate concentration. The calibration curve of the present immunometric hCRP assay was found to be linear over a wide range, approximately 4 orders of magnitude of hCRP concentration, the detection limit of the protein being 0.3 ng mL(-1) (mean background + 2SD) on CV values of about 10-30%, depending on the immunoassay incubation time. In the ECLIA measurements, different incubation times were tested from 15 min (giving above-mentioned performance) to as short as only 2 min, which still gave successful results with approximately 20,000 times better detection limit levels than traditional commercial assay methods. During the ECLIA process, also the Si electrode surface morphology was also investigated by atomic force microscope monitoring.