Europium chelate

An eel of an europium (III) chelate was reported before (60 ). The complex was not involved in the electrolysis. Excited organic compounds formed electrochemically underwent an intermolecular energy transfer to the emitting Eu compound. Interestingly, in the absence of the redox-active organic compounds an eel of the europium chelate was not observed 2+... 

Organic fluorescent dyes with the appropriate spectral properties also can be paired with lanthanide chelates in FRET systems. For instance, many rhodamine dyes and the cyanine dye Cy5 have ideal excitation wavelengths for receiving energy from a nearby europium chelate. The LeadSeeker assay system from GE Healthcare incorporates various Cy5-labeled antibodies for developing specific analyte assays. In addition, if using a terbium chelate as the donor, then a Cy3 fluorescent dye can be used in assays as the acceptor. 

Figure 9.52 The isothiocyanate group of a TMT europium chelate can be used to label amine-containing proteins and other molecules to result in an isothiourea bond.

Figure 9.55 A carbostyril-DTPA europium chelator is a strong enhancer of lanthanide luminescence. The chemical structure and three-dimensional structure of the chelator are shown.

Diamandis, E.P., and Christopoulos, T.K. (1990) Europium chelate labels in time-resolved fluorescence immunoassays and DNA hybridization assays (Review). Anal. Chem. 62, 1149-1157. 

Scorilas, A., Bjartell, A., Lilja, H., Moller, C., and Diamandis, E.R (2000) Streptavidin-polyvinylamine conjugates labeled with a europium chelate Applications in immunoassay, immunohistochemistry, and microarrays. Clin. Chem. 46, 1450-1455. 

Figure 7.13 Decay curve for europium chelates showing reading time after the...

Homogeneous TR-FIAs have been reported in which proprietary lanthanide chelates are used. In a homogeneous immunoassay for T4, a fluorescent europium chelate coupled to thyroxine is quenched by antibody binding. 90 A similar approach is used for estrone-3-glucuronide. 91 TRFIAs based on homogeneous methods have not yet become widely used. 

E. P. Diamandis and R. C. Morton, Time-resolved fluorescence using a europium chelate of 4,7-bis(chlorosulfophenyl)-l,10-phenanthroline-2,9-dicarboxylic acid (BCPDA). Labelling procedures and applications in immunoassays, J. Immunol. Methods 112, 43-52 (1988). 

M. J. Khosravi and E. P. Diamandis, Immunofluorometry of choriogonadotropin by time-resolved fluorescence spectroscopy, with anew europium chelate as label, Clin. Chem. 33, 1994-1999 (1987). 

Braunwalder, A.F., Yarwood, D.R., Sills, M.A., and Lipson, K.E., Measurement of the protein tyrosine kinase activity of c-SRC using time-resolved fluorometry of europium chelates, Anal. Biochem., 238, 159, 1996. 

Self (S4) first proposed the concept of noncompetitive assay for haptens utilizing an adequate combination of an a-type and a jS-type anti-idiotype antibody, in which he used the term, selective antibody for the a-type antibodies. Then, Barnard and Cohen (Bl) applied this assay principle for the determination of serum E2, naming the assay system an idiometric assay. Figure 12A illustrates the assay procedure of the idiometric assay of E2. The target hapten is captured by excess anti-E2 antibody immobilized on microtiter strips by incubation at room temperature for 1 h (step i). After washing the strips, the /3-type anti-idiotype antibody was added in order to saturate (or block) the unoccupied paratope of the anti-E2 antibody (incubation, room temperature for 30 min) (step ii). The a-type anti-idiotype antibody, which has been labeled with a europium chelate (H4), was then added to the plate and incubated at room temperature for a further 2 h (step iii). Finally, fluorescence intensity due to bound europium was measured with a time-resolved fluorometer. Because of large steric hindrance around the bound jS-type antibody (MW 150,000), the labeled a-type antibody would. 

Ye ZQ, Tan MQ, Wang GL, Yuan JL (2004) Novel fluorescent europium chelate-doped silica nanoparticles preparation, characterization and time-resolved fluorometric application. J Mater Chem 14 851-856... 

Bhaumik (148) measured the rise time of the red fluorescence in some europium chelates. His data were collected with a stroboscopic instrument having a time-resolution capability of around 0.2 /xsec. Figure 40 shows the fluorescence-rise curve of the sDq- >1F2 transition in the piperidine adduct of the four-ligand europium dibenzoylmethide chelate. Data were collected at 77°K. 

Halverson et al. examined the fluorescent lifetimes and quantum efficiencies of a very large number of compounds. Their data on the luminescence of various europium chelates and synergic agent complexes demonstrates the efficacy of the sheath. 

E. P. Diamandis and T. K. Christopoulos, Europium Chelate Labels in Time-Resolved Fluorescence Immunoassays and DNA Hybridization Assays, Anal. Chem. 1990, 62, 1149A. 

In accordance with the proportionality (3.8 a), the magnitude of the pseudocontact shift, which predominates for lanthanide shift reagents, decreases with the distance of nucleus i from the paramagnetic ion. Thus, C-9 of camphor is shifted more than C-10 on addition of the europium chelate. Often, the crude approximation (3.8 a) is a valuable assignment aid. 

Salicylates.—In the course of his intramolecular energy transfer studies (p. 130) on europium chelates Weissman 630 prepared the 3-nitro and 5-nitro salicylate complexes. He was one of the first to demonstrate the phenomena of intramolecular energy transfer (IMET) from the coordinated ligands to the central rare earth ions giving characteristic fluorescence of the metal ions. However, no analytical data on these compounds are available. 

The use of europium chelates, with their unusually long fluorescence decay times, as labels for proteins and antibodies has provided techniques that are referred to as time-resolved fluoroimmunoassays (TRFIA). Fluorophores as labels for biomolecules will be the topic of Sect. 3. Nevertheless, TRFIAs always have to compete with ELISA (enzyme-linked immunosorbent assays) techniques, which are characterized by their great versatility and sensitivity through an enzyme-driven signal amplification. Numerous studies have been published over the past two decades which compare both analytical methods, e.g., with respect to the detection of influenza viruses or HIV-1 specific IgA antibodies [117,118]. Lanthanide luminescence detection is another new development, and Tb(III) complexes have been applied, for instance, as indicators for peroxidase-catalyzed dimerization products in ELISAs [119]. 

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