Sakari Kulmala

Cathodically induced time-resolved lanthanide(III) electroluminescence at stationary aluminium disc electrodes

Abstract A time-resolved electroluminometer, which utilizes electrogenerated luminescence (EL) from disposable oxide-covered aluminium electrodes, is described in detail. The cathodic polarization of this disc electrode in aqueous electrolytes induces a faint background EL with peak emission at 570 nm and with a lifetime of 6 μs. This cell can be utilized to excite dysprosium(III), samarium(III) and terbium(III) by electrochemical means to their lowest excited singlet states and, thus, to produce lanthanide(III)-specific emissions. From the lanthanide(III) El systems tested so far, a cathodically induced EL of 2,6-bis[ N , N ,bis(carboxymethyl)aminomethyl]-4-benzoylphenol-chelated terbium(III) with a 2.1-ms lifetime is the longest lived and can be efficiently discriminated against the background EL on a time-resolved basis using instrumentally simple time-resolved detection; this time-resolved terbium(III) EL makes possible the determination of terbium(III) even below the picomole level in aqueous solutions.

Immunoassay by time-resolved electrogenerated luminescence

Abstract An immunoanalytical method based on electrogenerated luminescence was developed in which the labelling compound is the terbium chelate of 2,6-bis[ N,N -bis(carboxymethyl)aminomethyl]-4-benzoylphenol which is linked by a thioureido group to the antibody. The sandwich complex of the labelled antibody, antigen and antibody immobilized on the surface of an aluminium electrode is excited by an electrical pulse and, after a short delay from the end of the pulse, light emission is measured. The electroluminescence immunoassay is exemplified by the heterogeneous and homogeneous assays of human pancreatic phospholipase A 2 , for which both assay methods give a reasonably good linearity in the range 10–300 ng ml −1 .

Hot Electron Injection into Aqueous Electrolyte Solution from Thin Insulating Film-Coated Electrodes

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 film-coated electrodes to aqueous electrolyte solution. 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.

Mechanism of electrogenerated luminescence of terbium(III)-“2,6-bis[N,N-bis(carboxymethyl)aminomethyl]-4-benzoylphenol” chelate at an oxide-covered aluminium electrode

Abstract Generation of hydrated electrons at an oxide-covered aluminium electrode during its cathodic pulse-polarization in an aqueous electrolyte may well be the primary step of the electrogenerated luminescence of aromatic Tb(III) chelates. In the presence of appropriate precursors, hydrated electrons produce secondary oxidizing radicals, thus resulting in an energetic electrode/electrolyte interface which initiates the radiative 5D4 → 7Fj transitions of chelated terbium(III); the aromatic moiety of a Tb(III) chelate is excited by its consecutive interactions with hydrated electron and the secondary oxidizing radical followed by an intramolecular transfer of this excitation energy to the 5D4 level of coordinated terbium(III).

Feasibility of low-voltage cathodic electroluminescence at oxide-covered aluminum electrodes for trace metal determinations in aqueous solutions

Abstract Metal-catalyzed electroluminescence is generated at an oxide-covered aluminum electrode during the reduction of oxygen, potassium peroxodisulfate, and especially hydrogen peroxide in aqueous solutions. The feasibility of this electroluminescence for the determination of copper (5 × 10−9 M) and thallium (> 10−10 M) is demonstrated.

Hot electron-induced electrogenerated chemiluminescence of rare earth(III) chelates at oxide-covered aluminum electrodes

Aromatic Gd(III) and Y(III) chelates produce ligand-centered emissions during cathodic pulse polarization of oxide-covered aluminum electrodes, while the corresponding Tb(III) chelates produce metal-centered5D4 →7Fj emissions. It was observed that a redox-inert paramagnetic heavy lanthanoid ion, Gd(III), seems to enhance strongly intersystem crossing in the excited ligand and direct the deexcitation toward a triplet-state emission, while a lighter diamagnetic Y(III) ion directs the photophysical processes toward a singlet-state emission of the ligand. The luminescence lifetime of Y(III) chelates was too short to be measured with our apparatus, but the luminescence lifetime of Gd(III) chelates was between 20 and 70 μs. The mechanisms of the ECL processes are discussed in detail.

Electrogenerated luminescence of terbium(III) in aqueous solutions

Abstract It is demonstrated that oxide-bound terbium(III) at an aluminium electrode surface can be excited electrochemically to its lowest singlet state in aqueous electrolytes. The relaxation of this excited state to the vibrational ground states induces the well known narrow-band terbium(III) emissions at the peak wavelengths of 489, 548, 586 and 620 nm. In the presence of hydrogen peroxide and potassium peroxodisulphate, this cathodic electrogenerated luminescence (EL) can be used to produce an analytically feasible response for terbium(III) cation in aqueous solutions even at the 10 −8 M level. A detailed reaction scheme is presented for this cathodic terbium(III) EL and its utilization as an EL-based probe for environmental and clinical trace analysis is proposed.

Optical sensing of sulfite with a phosphorescent probe

Abstract Spectral-luminescent properties and quenching behavior of the covalent conjugate of the platinum(II) complex of coproporphyrin-I and bovine serum albumin (PtCP–BSA) was investigated. Quenching of phosphorescence by sulfite was studied in detail in an acidic range as a function of pH. Strong dynamic quenching of the phosphorescence by sulfite occurred at pH below 4.0 which was attributed to the formation of sulfur dioxide. The quenching reached its maximal level at pH below 1.5, Stern–Volmer quenching constants being as high as 2000xa0M−1. A new flow-injection system for the determination of sulfite was developed based on the PtCP–BSA conjugate immobilized on a preactivated Biodyne ABC membrane and placed in a flow-cell, with an acidic carrier buffer and fiber-optic phosphorescent detector. Such a solid-state phosphorescent probe is quenchable by sulfite and allowed rapid on-line detection of sulfite with a detection limit of about 10xa0μM. Performance of the new system and possible interferences were investigated.

Tb(III) chelate chemiluminescence induced by the dissolution of additively coloured potassium chloride in aqueous solutions of peroxydisulphate ions

Abstract Dissolution of an additively coloured alkali halide crystal in an aqueous peroxydisulphate solution results in the formation of hydrated electrons and sulphate radicals. These radicals are capable of inducing terbium(III) chelate chemiluminescence by fast subsequent redox reactions, where the radiative 5D4 → 7Fj transitions of coordinated terbium(III) is based on a chemical excitation of the aromatic ligand by its interactions with these radicals, which is followed by an intramolecular transfer of this excitation energy to the 5D4 state of terbium(III).

Terbium(III) lyoluminescence induced by the dissolution of UV-irradiated potassium peroxodisulfate in aqueous solutions

Abstract The ue5f8Oue5f8Oue5f8 bond of solid potassium peroxodisulfate can be ruptured by UV irradiation, which results in a solid solution of sulfate radicals in potassium peroxodisulfate. The dissolution of this irradiated solid in water produces a solid/solution interface rich in hydrated sulfate radicals, which can either recombine to form peroxodisulfate ions, or react with solvent or solutes in a sample solution. In terbium(III)-containing aqueous solutions, this dissolution produces the characteristic radiative 5 D 4 → 7 F-multiplet transitions of terbium(III). This study points out that the light-emitting pathway of this terbium(III) lyoluminescence consists of the following steps: (i) hydrated sulfate radical oxidizes terbium(III) to terbium(IV), (ii) terbium(IV) is immediately reduced by water via a process that is sufficiently energetic to leave the resulting terbium(III) in its lowest excited state 5 D 4 and finally, (iii) the relaxation of this excited 5 D 4 state of terbium(III) induces the aforementioned transitions. Thus, this terbium(III) lyoluminescence can be also classified as chemiluminescence. In addition, x-ray irradiated potassium peroxodisulfate is capable of generating an analogous terbium(III) lyoluminescence, which is, however, investigated only on qualitative basis. Lyoluminescence generation of both irradiated materials can be used to determine hydrated Tb(III) down to the micromolar level in aqueous solutions.