Luminescence lanthanide ions/complexes

Assays based on luminescent lanthanide ions were developed initially in the 1970s, when instrumentation became available which could distinguish long-lived luminescence from a shortlived background. Leif and co-workers reported the first attempts to use lanthanide complexes (in this case europium complexes with 1,10-phenanthroline and 7-diketonates, i.e., [Eu(phen)(diketo-nate)3]) as tags for antibodies.107 These proved kinetically unstable in the pH regime required... 

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. 

Steemers, F.J., Verboom, W, Reinhoudt, D.N., et al (1995) New sensitizer-modified calix[4]arenes enabling near-UV excitation of complexed luminescent lanthanide ions. Journal of the American Chemical Society, 117, 9408-9414. 

Figure 13.4 Typical design principle of lanthanide complex-based chemosensors based on binding of an analyte (an) (a) directly influencing the Ln(III) luminescence, (b) influencing photophysical properties of the ligand, and (c) addition of a sensitizing analyte onto a poorly luminescent lanthanide-containing sensor [1]. (Reproduced from J.C.G. Bunzli and C. Piguet, Taking advantage of luminescent lanthanide ions, Chemical Society Reviews, 34, 1048-1077, 2005, by permission of The Royal Society of Chemistry.)...

Lanthanide ions exhibit long-lived, strong luminescence in the visible region. Their f f absorption bands are, however, very weak and FRET to lanthanide ions is thus inefficient. Efficient FRET and even two-photon absorption118 can be achieved by complexation with appropriate chromophores as an antenna. Lanthanide ion complexes (Figure 2.21) are used... 

For coordinating and sensing luminescent lanthanide ions, a luminescent ruthenium bipyridyl complex has been covalently linked to one, two or six lower rim acid-amide modified caUx[4]arene moieties in receptors 155-157. All these complexes coordinated with lanthanide ions, Nd , Eu and Tb, with the formation of adducts of variable stoichiometries. The adduct formation affected the Ru luminescence, which was strongly quenched by Nd ion, increased by the Tb ion and moderately quenched or increased by Eu ion (2004IC3965). 

Excitation of Near-hifrared Luminescent Lanthanide Ions and Complexes. 152... 

Concerning the luminescence of the second group of NIR luminescent lanthanide ions, the ions Tm and Ho " display even weaker luminescence in solution than Nd and Er, and the luminescence of their complexes has only... 

The first two chapters of this work cover theoretical and practical aspects of the emission process, the spectroscopic techniques and the equipment used to characterize the emission. Chapter 3 introduces and reviews the property of circularly polarized emission, while Chapter 4 reviews the use of lanthanide ion complexes in bioimaging and fluorescence microscopy. Chapter 5 covers the phenomenon of two-photon absorption, its theory as well as applications in imaging, while Chapter 6 reviews the use of lanthanide ions as chemo-sensors. Chapter 7 introduces the basic principles of nanoparticle upconversion luminescence and its use for bioimaging and Chapter 8 reviews direct excitation of the lanthanide ions and the use of the excitation spectra to probe the metal ion s coordination environment in eoordination compounds and biopolymers. Finally, Chapter 9 describes the formation of heterobimetallic complexes, in whieh the lanthanide ion emission is promoted through the hetero-metal. 

Until very recently, studies of the use of luminescent lanthanide complexes as biological probes concentrated on the use of terbium and europium complexes. These have emission lines in the visible region of the spectrum, and have long-lived (millisecond timescale) metal-centered emission. The first examples to be studied in detail were complexes of the Lehn cryptand (complexes (20) and (26) in Figure 7),48,50,88 whose luminescence properties have also been applied to bioassay (vide infra). In this case, the europium and terbium ions both have two water molecules... 

Kawa, M., and Frechet, J.M.J. (1998) Self-assembled lanthanide-cored dendrimer complexes enhancement of the luminescence properties of lanthanide ions through site-isolation and antenna effects. Chem. Mater. 10, 286-296. 

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