Jouko Kankare

Correlation between the lowest triplet state energy level of the ligand and lanthanide(III) luminescence quantum yield

Abstract The luminescence properties of 41 different Eu(III) and Tb(III) chelates that were synthesized with the purpose of developing new markers for chemical and biochemical applications were measured in aqueous solution and their suitability for labels in time-resolved immunoassays were evaluated. In spite of the influence of numerous factors on the luminescence quantum yields, a clear correlation was obtained between the energies of the lowest triplet state levels of the ligands and lanthanide (III) luminescence quantum yields of the respective chelates. Simultaneously Eu(III) and Tb(III) ions were observed to accept energy by their several different 5Dj, resonance levels depending on the energy of the lowest triplet state level of the ligand, and the Tb(III) luminescence quantum yields were observed to decrease due to the energy back transfer from excited Tb(III)∗ to the ligand when the energy difference between the 5D4 level of Tb(III) and the lowest triplet state energy level of the ligand is less than 1850 cm−1.

In situ spectroelectrochemical characterization of poly(3,4-ethylenedioxythiophene)

The electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT), in diAerent electrolyte‐solvent media was studied with cyclic voltammetry, in situ UV‐VIS-spectroelectrochemistry, electrochemical quartz crystal microbalance technique (EQCM) and with in situ Fourier transform infrared (FTIR) spectroscopy using external and internal reflection techniques. The eAect of polymerization current density and monomer concentration on the formation of the film structure was studied. The redox reactions and the stability of charged films of diAerent thickness were studied with cyclic voltammetry and open circuit potentiometric measurements. FTIR spectra were recorded in situ during step-wise and continuous potential cycling of the polymer films in diAerent electrolytes. A characterization of the doping induced IR-bands has been made. # 1999 Elsevier Science Ltd. All rights reserved.

The mechanism of the electrogenerated chemiluminescence of luminol in aqueous alkaline solution

Abstract The mechanism of the electrogenerated chemiluminescence of luminol in aqueous alkaline solution based on the rotating ring—disc electrode system is discussed. The disc electrode is maintained at a negative potential and the ring electrode at a symmetrically changing double-step potential. Hydrogen peroxide generated at the disc electrode by the reduction of oxygen is immediately transported to the ring electrode because of electrode rotation. Hydrogen peroxide and luminol are oxidized at the ring electrode during the positive pulse of the double-step potential. These oxidation processes generate a superoxide radical and a luminol radical as intermediates. The luminol radical reacts with the superoxide radical (or oxygen) emitting light.

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.

In-situ conductance measurement during electropolymerization

Abstract A mathematical model for the conductance of a growing conductive polymer layer on a double-band electrode has been developed. The model, which is based on the theories of conformal mapping and elliptic integrals, predicts that conductance is linearly related to the conductivity and approximately to the logarithm of the thickness of the polymer layer. A new type of ac conductimeter based on a double current follower has been constructed in order to monitor conductance during the electrochemical polymerization on a double-band microelectrode. By recording conductance during the galvanostatic polymerization of pyrrole and 3-methylthiophene the conductivities were obtained from the slope of the linear section of the graph vs logarithm of time and the growth rate from its intercept. The conductivity of polypyrrole-dodecylsulfate was in accordance with the reported values. The conductance of poly(3-methylthiophene) showed a catastrophic decline after a prolonged electropolymerization, presumably as a result of the known “polythiophene paradox”, i.e. polymerization potential being outside the stability range of the polymer. The method allows a facile measurement of the specific conductivity of a polymer without the need for calibration with materials of known conductivity and thickness.

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 .

Potentiometric response of conducting polymer electrodes for oxygen in neutral aqueous solutions

The effect of oxygen on the potential of electrodes coated with a thin layer of various conducting polymers and immersed in aqueous neutral buffer solution has been studied. A theoretical equation describing the dependence of the potential on the concentration of oxygen has been derived and shown to be in conformity with the experimental results for polyaniline, polypyrrole, and poly(3-methylthiophene). The theory is based on the formation of charge-transfer complexes between oxygen molecule and the reduced (undoped) form of conducting polymer.

Electropolymerization of pyrrole: Effects of pH and anions on the conductivity and growth kinetics of polypyrrole

Polypyrrole is one of the most studied conducting polymers. In situ AC conductimetry during electropolymerization is a method which allows the specific conductivity to be estimated for the polymer in statu nascendi. We have applied this method to the electropolymerization of pyrrole in aqueous solutions at various conditions. Polymers synthesized at lower pH range are of better quality than those synthesized at higher pH values. The use of small anions in the supporting electrolyte results in a layer of low conductivity at pH 7. The use of long-chain organic anions like sodium dodecylsulfate gives a high quality polymer even in neutral unbuffered solutions.

In situ ftir spectroelectrochemical characterization of poly(3,4-ethylenedioxythiophene) films

The electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT) and the redox behavior of poly(3,4-ethylenedioxythiophene) (PEDOT) were studied using electrochemical techniques and in situ internal reflection FTIR spectroscopy. A comparison of the IR spectra of PEDOT films taken during charging and discharging in different electrolytes is reported.

Lanthanide chelates as new fluorochrome labels for cytochemistry.

Anti-rabbit IgG labeled with a new fluorescent europium chelate was used to localize rabbit IgG to human smooth muscle myosin in a histological section. The antibody labeled with the europium chelate could be viewed with a conventional fluorescence microscope with a steady-state light source. This result encourages the development of a time-resolved fluorescence microscope, because a significant improvement in the signal-to-noise ratio can be anticipated.