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A research on the effect of different buffers on the pH range of 6–10 on the thin oxide-covered surface of aluminum cathode has been conducted under the conditions corresponding with those generally used in bioaffinity assays or other determinations made by using aluminum probe based on time-resolved cathodic electrochemiluminoimmuno assay (tr-ECLIA or tr-CECLIA) detection. The experiments have been conducted on impedance and cathodic electrochemiluminescence (CECL) basis using a strong long lifetime having electroluminophore Tb(III)-1 chelate where the ligand 1 is 2,6-bis[N,N-bis(carboxymethyl)aminomethyl]-4-benzoylphenol and Ruthenium(II) tris(2,2′–bipyridine) (Ru(bpy)32+) as the CECL model luminophores. The results point out that the natural oxide layer at the electrode surface does not essentially change as to its thickness but as to its resistance, it can be concluded that the best buffer in these luminophore determinations based on CECL and Al probe use is borate buffer adjusted to pH around 7–8 where the surface of aluminum has its neutral character. In the bioaffinity assays the meaning of the buffer seems to be more difficult to realize due to the complex character of the surface with plenty of different coatings and special handling steps but still with the aforementioned borate buffer the results were noticed to be the most stabile. The tests also pointed out that the character of the pure aluminum surface and the oxide layer above it without any other coatings could be strongly affected by the surrounding solution composition and in that way to the durability of the aluminum probe already during the quite short exposure times. The reported results are useful especially in the field of CECL based on aluminum probe use but could also in a certain extent to be utilized in a large scale of analysis considering the use of aluminum probes.

Tris(2,2′-bipyridine)ruthenium(II) chelate exhibits strong electrogenerated chemiluminescence during cathodic high-voltage pulse-polarization of pointed Pt electrode in aqueous solutions. The present method is based on a field emission or other type of tunnel emission of hot electrons into an aqueous electrolyte solution. The method allows the detection of tris(2,2′-bipyridine)ruthenium(II) and its derivatives below nanomolar concentration levels and yields linear log-log calibration plots spanning several orders of magnitude of concentration.

Time-resolved electrogenerated chemiluminescence of multidentate phenolic Eu(III) chelates were studied in aqueous solution. 2,6-bis[N,N-bis(carboxymethyl)-aminomethyl]-4-benzoylphenol forms a photoluminescent and electrochemiluminescent Eu(III) chelate, whereas 2,6-bis[N,N-bis(carboxymethyl)-aminomethyl]-4-methyl phenol-chelated Eu(III) turned out to be not luminescent at all. The importance of the redox properties of both the ground and the excited states of the ligands and the central ion is shown. The former chelate shows relatively weak ECL at an oxide-covered aluminum electrode but the ECL intensity can be strongly enhanced by the addition of peroxodisulfate ions. In the presence of 1 mM peroxodisulfate ions the ECL lifetime of this chelate is 0.94 ms, thus easily allowing time-resolved detection of the chelate. This chelate can be conjugated to antibodies by thioureido linkage and used as an electrochemiluminescent label in immunoassays as a marker which displays long-lived luminescence in the red end of the optical spectrum. The present ECL is mainly based on the ligand sensitized redox excitation of the chelate by analogous pathways to those known from the studies of aromatic Tb(III) chelates but the energy transfer from the emission centers of the aluminum oxide film can also have minor contribution to the excitation of the label.

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.

Ruthenium(II) tris(2,2′-bipyridine) chelate shows chemiluminescence (CL) both during dissolution of metallic aluminium in alkaline conditions, and during dissolution of magnesium metal in acidic conditions. The presence of peroxodisulfate ions strongly enhances the CL. Magnesium system provides considerably better detectability of the present chelate giving linear calibration plot spanning over many orders of magnitude of concentration down to subnanomolar concentration levels. The possible primary species generated and luminescence mechanisms are shortly discussed.

Hot electrons can be injected from conductor/insulator/electrolyte (C/I/E) junctions into an aqueous electrolyte solution. Injected hot electrons induce electrogenerated chemiluminescence (ECL) of various luminophores in fully aqueous solutions. Such ECL gives the basis of electrochemiluminoimmunoassays and DNA-probe assays where different luminophores can be used as electrochemiluminescent labels. This work shows that SYBR® Green I is suitable as an ECL label in detection methods based on C/I/E tunnel-emission electrodes such as oxide-coated aluminium, magnesium and silicon electrodes.

A bicapped [60]fullerene–γ-cyclodextrin complex has been prepared in an aqueous boric acid–caesium borate buffer. It is shown that this water-soluble complex generates an anomalous [60]fullerene specific blue–green emission at the cathodically polarized aluminium/aluminium oxide interface but not at the zirconium/zirconium oxide and tantalum/tantalum oxide interfaces. A mechanistic pathway for the formation of this emission is proposed: the cathodic polarization of the aluminium/aluminium oxide interface injects a hot electron from the conduction band edge of the aluminium oxide to the higher acceptor levels 2t2g and/or 4ag of [60]fullerene. The relaxation of these acceptor levels to the 5t1u level (LUMO) of [60]fullerene initiates the intense emission peaking at around 445 nm. Further, use of this cathodic electroluminescence (EL) for the recognition of [60]fullerene from its mixtures with higher fullerenes is proposed.

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).

The near-infrared electrogenerated chemiluminescence (IR ECL) of Yb(III) chelates at a pulse-polarized oxide-covered aluminium cathode is described for the first time. The observed 2 F 5/2 → 2 F 7/2 radiative transition of Yb(III) is the lowest-energy ECL in aqueous solution reported to date. Also, a proposed explanation for the excitation and emission processes of this near-IR ECL of Yb(III) chelates has been given. The phenomenon offers many new application possibilities for analytical purposes, for example, a new point of view for wavelength discrimination.

Dissolution of X-ray irradiated sodium chloride or additively coloured potassium chloride induces generation of hydrated electrons which produce thallium(I)-specific chemiluminescence in the presence of thallium(I) ions. Such a luminescence is also called extrinsic lyoluminescence (ELL) of X-ray irradiation coloured sodium chloride, or additively coloured potassium chloride. The present ELL is considered chemiluminescence induced by dissolution-produced strong reducing and oxidising agents, i.e. hydrated electrons, surface-bound and only partially hydrated hole centres, and hydroxyl or sulphate radicals (in the case of additively coloured potassium chloride dissolved in solution containing peroxodisulphate ions). Dichlorothallate(I) (Tl(I)Cl − 2 ) was the main emitter in the ELL processes at about 430 nm. The reduction-initiated excitation pathway of TlCl − 2 involves a colloidal thallium atom surrounded by chloride anions (Tl(O):2Cl − ) while in the less important oxidation-initiated excitation pathway the precursor of excited Tl(I)Cl − 2 is transiently existing Tl(II)Cl − 2 produced by dissolution-uncovered hole centres (or sulphate radicals). Both of the lyoluminescence procedures allow Tl(I) to be detected below nanomolar concentrations, yielding linear log–log calibration plots spanning several orders of magnitude of concentration.

Energy transfer between aluminium oxide F-center and lanthanide cations at an oxide-covered aluminium electrode during the cathodic pulse-polarization of the electrode is investigated by means of Stern-Volmer luminescence quenching kinetics. Terbium III -specific extrinsic luminescence is observed while some other lanthanides are observed to quench the F-center luminescence. Different quenching efficiencies of the lanthanides are discussed to be dependent on the different energy acceptor characteristics of the tri- or divalent lanthanides.

1-Aminonaphthalene-4-sulfonate (ANS)-specific extrinsic lyoluminescence (LL) of X-ray irradiated sodium chloride is observed at 425 nm when the irradiated salt is dissolved in an aqueous solution of ANS. The paper discusses, in detail, the mechanism of the ANS-specific LL and its analytical applicability. Also, the intrinsic LL of X-ray irradiated sodium chloride is studied. Hydrated electron as well as hole scavenger experiments support the proposal that in the case of the intrinsic LL of X-ray irradiated sodium chloride, trapped electrons (mainly F-center electrons) are released and hydrated whereas trapped holes (V-centers) remain surface-bound and are only partially hydrated before recombination occurs. These hydrated electrons and dissolving solid surface-bound hole centers, which are probably only partially hydrated, are able to act as reducing and oxidizing agents, respectively, in the luminophore oxidation-initiated reductive excitation pathway of ANS. Solution additives (halides and pseudohalides) show that in the chemiluminescence processes in question, oxidizing agents will follow the Marcus theory of electron transfer reactions. The LL method described allows the determination of ANS in the concentration range ≈10 −11 − 10 −7 M. This suggests that aminonaphthalene derivatives can be used as label molecules in high sensitivity lyoluminobioaffinity assays.

A pulse-polarization of an oxide-covered aluminium cathode in an aerated aqueous buffer containing micelle-incorporated [60]fullerene and [70]fullerene generates fullerene specific emissions at λ 440 nm and λ 425 nm which respond to the fullerene concentrations down to around 10 -7 M.

TbIII chelates containing aromatic moieties show sonoluminescence in aqueous solutions during the sonolysis of water. The observed 5D4→7FJ transitions of TbIII are due to the excitation of ligand, followed by an intramolecular energy transfer from the ligand to the central ion, which finally emits. No sonoluminescence of hydrated or EDTA-chelated TbIII ion could be observed. Ligand excitation can be based either on an energy transfer from the intrinsic emission centres of the sonolysis of water to the aromatic ligand, or on redox reactions between the ligand and hydroxyl radicals and hydrogen atoms produced by the sonolysis of water. Experimental results give greater support to the latter, chemiluminescent, excitation pathway.

An instrumentally simple on-column time-resolved luminescence capillary electrophoresis (CE) detector for determining and characterizing migrated europium(III) chelates on the basis of their long-lived 5D0→7F-multiplet transitions has been constructed. In addition to the background fluorescence arising from the cell walls, this time-resolved luminescence method of measurement also allows an efficient discrimination of the analyte emission against the short-lived background fluorescence caused by possible fluorescent impurities in the electrophoresis buffer; this should provide a feasible means of constructing a CE detector for the trace analysis of europium(III) chelates and also of samples of biological interest labelled with europium(III) chelates. If supplied additionally with a device for determining the excited-state lifetimes of separated europium(III) chelates, this time-resolved luminescence detector should make possible the peak identification of migrated europium(III) chelates.

Some of the luminescent aromatic Tb(III) chelates can be excited at oxide-covered magnesium and n-ZnO:Al/MgO composite electrodes by cathodic pulse polarization in aqueous solution. This is based on the cathodic injection of hot electrons into the aqueous electrolyte solution and successive redox reactions in one-electron steps resulting in the excited states of the chelates. Due to the relatively long luminescence lifetime of multidentate Tb(III) chelates, these chelates can be very sensitively detected by time-resolved electrochemiluminescence (TR-ECL) measurements using the present working electrodes. Thus, metal or highly doped semiconductor electrodes coated by a thin MgO film lend themselves as nontransparent or in some cases, even optically transparent working electrodes for generation of free radicals and cathodic ECL in aqueous solution. The results suggest that also other even more efficient optically transparent composite tunnel emission electrodes than the present n-ZnO:Al/MgO electrodes could be constructed by coating n-ZnO:Al glass electrodes with other wide band gap insulating oxides.