Veli-Matti Mukkala

Europium as a label in time-resolved immunofluorometric assays

A nonisotopic immunoassay has been developed based on a sensitive detection of europium (III) in water solution using time-resolved fluorometry. The europium label is bound to the antibody with EDTA derivatives, either diazophenyl-EDTA-Eu or isothiocyanatophenyl-EDTA-Eu. After the immunometric assay has been completed the europium is preferably dissociated from the antibody at low pH and measured by time-resolved fluorescence in a micellar solution containing Triton X-100, beta-diketone, and a Lewis base. The detergent solubilizes the chelating compounds in the solution and excludes water from the fluorescent ligand-europium complex. Europium concentrations as low as 5 X 10(-14)M were measured using a 1-s counting time. The sensitivity of the immunoassay of rabbit IgG used as a model system was 25 pg/ml (6 pg/assay).

Time-Resolution in Fluorometry Technologies, Labels, and Applications in Bioanalytical Assays

Referee: C. Morgan, School of Environmental and Life Sciences. University of Salford, U.K.

Co-fluorescence of europium and samarium in time-resolved fluorimetric immunoassays

In the presence of an excess of Y3+, the fluorescence intensities of Eu3+ and Sm3+, chelated with benzoyltrifluoroacetone (BTA) or thenoyltrifluoroacetone (TTA) in an aqueous solution containing 1,10-phenanthroline, were increased by factors ranging from 209- to 811-fold. This co-fluorescence phenomenon was used in a highly sensitive time-resolved fluorimetric detection of the lanthanides, Eu3+ and Sm3+. The detection limits of Eu3+ in the BTA- and TTA-based solutions were 4 and 15 fmol dm-3, respectively. The detection limits of Sm3+ were 0.11 and 0.12 pmol dm-3, respectively. The co-fluorescence enhancement systems were also applied in the double-label time-resolved fluorimetric immunoassay of luteinizing hormone and follicle stimulating hormone using specific antibodies labelled either with Eu3+ or Sm3+. The co-fluorescence enhancement solution was superior as compared with the commercial direct fluorescence enhancement solution based on the acidic solution of beta-naphthoyltrifluoroacetone, trioctylphosphine oxide and Triton X-100, in respect to the signal level obtained and the sensitivity. It is suited to time-resolved fluorimetric immunoassays in which particularly high detection sensitivities are required, and it can also be used in double-label assays employing Eu3+ and Sm3+ chelate labels.

Novel luminescent samarium(III) chelates

Abstract A series of new stable, luminescent samarium(III) chelates were synthesized and their photophysical properties were measured. The iodoacetamido activated chelate coupled to a peptide was used in a caspase-3 assay.

The use of europium (Eu3+) labelled primers in PCR amplification of specific target DNA

The polymerase chain reaction (PCR) has many potential applications in the field of DNA probe diagnostics. Here we describe a method that utilizes PCR and time-resolved fluorometry (TRF) for the detection of specific target DNA. First the DNA segment to be detected is amplified according to standard procedures. Then a pair of europium (Eu3+) and biotin-labelled primers nested within the amplified fragment is incorporated in a few additional PCR cycles. Thus amplified DNA fragments are generated that contain an affinity label (biotin) and a detectable label (europium). The doubly-labelled amplified DNA fragments are collected onto streptavidin coated microtitration strips and the bound Eu3+ is measured in a time-resolved fluorometer. We show here the application of this method to the detection of HIV-1 DNA. As few as five copies of HIV-1 DNA could readily be detected using this assay. The method described here is sensitive, rapid and easy to employ. In addition it lends itself to automation.

A dissociative fluorescence enhancement technique for one-step time-resolved immunoassays

AbstractThe limitation of current dissociative fluorescence enhancement techniques is that the lanthanide chelate structures used as molecular probes are not stable enough in one-step assays with high concentrations of complexones or metal ions in the reaction mixture since these substances interfere with lanthanide chelate conjugated to the detector molecule. Lanthanide chelates of diethylenetriaminepentaacetic acid (DTPA) are extremely stable, and we used EuDTPA derivatives conjugated to antibodies as tracers in one-step immunoassays containing high concentrations of complexones or metal ions. Enhancement solutions based on different β-diketones were developed and tested for their fluorescence-enhancing capability in immunoassays with EuDTPA-labelled antibodies. Characteristics tested were fluorescence intensity, analytical sensitivity, kinetics of complex formation and signal stability. Formation of fluorescent complexes is fast (5xa0min) in the presented enhancement solution with EuDTPA probes withstanding strong complexones (ethylenediaminetetra acetate (EDTA) up to 100xa0mM) or metal ions (up to 200xa0μM) in the reaction mixture, the signal is intensive, stable for 4xa0h and the analytical sensitivity with Eu is 40xa0fmol/L, Tb 130xa0fmol/L, Sm 2.1xa0pmol/L and Dy 8.5xa0pmol/L. With the improved fluorescence enhancement technique, EDTA and citrate plasma samples as well as samples containing relatively high concentrations of metal ions can be analysed using a one-step immunoassay format also at elevated temperatures. It facilitates four-plexing, is based on one chelate structure for detector molecule labelling and is suitable for immunoassays due to the wide dynamic range and the analytical sensitivity.n Figurexa0

Detection of amplified HTLV-I/II viral sequences using time-resolved fluorometry

Since its discovery, the polymerase chain reaction (PCR) has been used for different purposes in the field of DNA research. We tested the PCR for the diagnosis of HTLV-I/-II infections. PCR was used to amplify 141- and 149-base pair regions from the HTLV-I and HTLV-II virus genomes, respectively. The annealing temperature in the PCR amplification was optimized using 20% polyacrylamide gels and silver staining. Even a slight change (3 degrees C) in the annealing temperature had an effect on the specificity of the reaction. The PCR products were detected with biotin and Eu-labeled oligonucleotide probes in a solution hybridization format. The linearity of the assay was tested with serial dilutions of purified chromosomal DNA containing integrated HTLV-II sequences. The linearity was found to be dependent on the number of cycles used in the PCR amplification. The best linearity, at a target level of a few copies, was achieved using a low number of cycles. The specificity of the assay was tested using HTLV-I and HTLV-II-infected lymphocytes from the cell lines Hut102 and MO480, respectively. No cross reactivity between these analytes was observed.

Synthesis and properties of nanospheres copolymerised with luminescent europium(III) chelates

Europium(III) chelates based on β-diketone and thienylpyridine subunits tethered to an acrylamide function were synthesized. They were polymerised with styrene and acrylic acid in the presence or absence of trioctylphosphine. The photophysical properties of the nanobeads obtained are also discussed.