Luminescence detection complexes

The opportunity of use of a ternary complex of ions Eu(III) with oxatetracycline (OxTC) and citrat-ions (Cit) for luminescent detection of OxTC in milk after chromatographic isolation is shown. 

The very first spectroscopic instruments, from Newton s prism and pinhole to Frauenhofer s simple spectroscope, were constructed to observe luminescence. Even though the great sensitivity of luminescence detection seemed to promise that luminescence would become an important tool for chemical analysis, the fact is that absorption spectroscopy was the first spectroscopic technique to be widely used. At first glance, this may seem surprising since absorption spectroscopy is inherently less sensitive and had to await the development of more complex instrumentation, especially, electronically amplified detection. 

Charbonniere, L. J. Ziessel, R. Montalti, M. Prodi, L. Zaccheroni, N. Boehme, C. Wipff, G. Luminescent lanthanide complexes of a bis-bipyridine-phosphine-oxide ligand as tools for anion detection. J. Am. Chem. Soc. 2002, 724(26), 7779-7788. 

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]. 

Ruthenium complexes have been applied successfully to the luminescent detection of proteins on blotting membranes like nitrocellulose [160]. The bipyridyl and phenanthroline complexes modified with aminoreactive NHS-ester or isothiocyanate groups are commercially available [161]. An even higher sensitivity and lower detection limit can be obtained by encapsulating... 

The formation of these ternary luminescent lanthanide complexes was the result of displacement of the two labile metal-bound water molecules, which was necessary because the energy transfer process between the antenna and the Ln(III) metal centre is distance-dependent. This ternary complex formation was confirmed by analysis of the emission lifetimes in the presence of DMABA and showed the water molecules were displaced by a change in the hydration state q from 2 to 0, with binding constants of log fCa = 5.0. The Eu(III) complexes were not modulated in either water or buffered solutions at pH 7.4. Lifetime analysis of these complexes showed that the metal-bound water molecules had not been displaced and that the ternary complex was not formed. Of greater significance, both Tb -27 and Tb -28 could selectively detect salicylic acid while aspirin was not detected in buffered solutions at pH 7.4, using the principle as discussed for DMABA where excitation of the binding antenna resulted in a luminescent emission upon coordination of salicylic acid to the complex. 

The detection of aromatic carboxylates via the formation of ternary complexes using lanthanide ion complexes of functionalised diaza-crown ethers 30 and 31 has been demonstrated [134]. Like the previous examples, these complexes contained vacant coordination sites but the use of carboxylic acid arms resulted in overall cationic 2+ or 1+ complexes. Furthermore, the formation of luminescent ternary complexes was possible with both Tb(III) and Eu(III). A number of antennae were tested including picolinate, phthalate benzoate and dibenzoylmethide. The formations of these ternary complexes were studied by both luminescence and mass spectroscopy. In the case of Eu-30 and Tb-30, the 1 1 ternary complexes were identified. When the Tb(III) and Eu(III) complexes of 30 were titrated with picolinic acid, luminescent enhancements of 250- and 170-fold, respectively, were recorded. The higher values obtained for Tb(III) was explained because there was a better match between the triplet energy of the antenna and a charge transfer deactivation pathway compared to the Eu(III) complex. 

In related work, Dong and Martin developed an assay that detects the catalytic activity of the enzymes pig liver esterase and porcine kidney leucine aminopeptidase by using substrates which have been labeled with metal-binding ligands [57], The enzymes catalyze changes in the substrates that affect their ability to bind to non-luminescent Ru complexes to form mixed-ligand complexes capable of ECL. 

Nieuwenhuizen and Harteveld [92] have realized a nerve agent dosimeter gas sensor based on the strong interaction between certain metal ions and organophosphorus compounds. In this case, the sensor material contains La(III) 2-bis(carboxymethyl)amino hexadecanoic acid and different factors such as humidity, concentration and layer thickness have been studied and optimized. Using a combination of a metallic complex with a molecular-imprinted polymer, a very sensitive sensor was developed for the detection of soman, a chemical warfare agent (the detection limit was 7 ppt) [93]. The biosensing material is based on a polymer coated onto a fiber-optic probe modified with a luminescent europium detection complex. This complex was... 

The luminescent cyclometalated complex [Pt(C4ANAN)py]+ 39 immobilized in Nafion film has been observed to exhibit a solvatochromic shift in emission maximum from 530 to 650 nm upon immersion in ethanol but no effect was detected with aprotic organic solvents (Fig. 19) [41]. On the contrary, the emission of the [Pt(C4ANAN)]+ luminophore anchored on silica materials (MCM-41/-48 and silica gel) showed a blue shift from Tmax 665 to 550 nm upon exposure to pentane vapor but no shift was observed for ethanol vapor (Fig. 20). 

Berggren K., Steinberg T. H., Lauber W. M., et al. (1999) A luminescent ruthenium complex for ultrasensitive detection of proteins immobilized on membrane supports. Anal Biochem 276(2), 129 3. 

Berggren, K., et al. (1999). A Luminescent Ruthenium Complex for Ultrasensitive Detection of Proteins Immobilized on Membrane Supports, , 4na/. Biochem. 276 129-143. 

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