Lanthanide‐Based Conjugates as Polyvalent Probes for Biological Labeling

Abstract

A series of lanthanide complexes of [LnL(H2O)] composition, suitable for biological labeling has been studied, in which L is a strongly chelating ligand containing chromophoric bipyridylcarboxylate units and Ln = Sm, Eu, Gd, Tb, and Dy. For the Gd complex, a combined 17O NMR and 1H NMRD study has been performed. The water exchange rate obtained, kex298 = (5.2 ± 0.6) × 106 s–1, is slightly higher than those for [Gd(dota)(H2O)]– or [Gd(dtpa)(H2O)]2–. Transformation of the uncoordinated carboxylate function of the ligand into an activated ester ensures covalent linking of the complex to bovine serum albumine (BSA). The relaxivity properties of the Gd complex labeled on BSA revealed a limited increase of both longitudinal and transversal relaxivities. This can be related to the partial replacement of the inner‐sphere water molecules by coordinating functions of the protein. Additionally, the Sm and Dy complexes are described and chemically characterized. Their photophysical properties were investigated by means of absorption, steady‐state and time‐resolved spectroscopy, evidencing efficient photosensitization of the lanthanide emission by ligand excitation (antenna effect). Luminescence lifetime measurements confirmed the presence of a water molecule in the first coordination sphere that partly explained the relatively poor luminescence properties of the Dy and Sm complexes in aqueous solutions. The spectroscopic properties of the series of complexes are questioned in terms of time‐resolved acquisition techniques. Finally, their availability for use in time‐resolved luminescence microscopy is demonstrated by staining experiments of rat brain slices, where the complex showed enhanced localization in some hydrophilic regions of the blood–brain barrier (BBB).(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Long-Lived Emissive Probes for Time-Resolved Photoluminescence Bioimaging and Biosensing

“…0.52 ns) was longer than that in pure water (0.45 ms), indicative of a higher microviscosity. 470 The TGL image with a delay time of 100 μs clearly showed that the chelate was localized in the regions of the choroid plexus, which was a part of the blood− brain barrier mainly composed of hydrophilic epithelial cells. Lu, Jin, and co-workers upgraded a high efficient dual-color lowbackground TGL microscope to by incorporation of synchronization of a high power flash lamp with high repetition rate (1 kHz) and a robust time-gating detection unit into a commercial epi-fluorescence microscope.…”

“…TGL imaging is more important and advantageous in organism and tissue imaging because the increased autofluorescence and scattering compromise the contrast of the nontime-gated imaging. A Tb (III) chelate 99 (see Chart ) was used to image rat brain slices . The TGL image with a delay time of 100 μs clearly showed that the chelate was localized in the regions of the choroid plexus, which was a part of the blood–brain barrier mainly composed of hydrophilic epithelial cells.…”

Lanthanide Luminescence for Biomedical Analyses and Imaging

“…The coupling is achieved either directly, e.g., in immunoassays in which the lanthanide probe is linked to a monoclonal antibody mAb, or indirectly, with the chelate being covalently bound to avidin (or biotin), and the resulting duplex being then fixed onto a biotinylated (or avidin derivatized) mAb via the strong avidin−biotin interaction (log K ≈ 10 15 ) . Alternatively, avidin may be substituted by streptavidin or bovine serum albumin (BSA) . Examples of indirect and direct coupling are depicted in Figure .…”

“…Multiparameter imaging is also feasible, as demonstrated by A. E. Soini et al, who used a combination of four different metal luminophores (Eu III , Tb III chelates, and Pd II , Pt II coproporphyrins) in conjunction with an organic marker (Syto 25) to image samples containing mixed populations of peripheral blood leukocytes; emission from the various luminescent stains was separated by time-resolved detection . Ligands bearing bipyridyl carboxylates units function as efficient antennae for several lanthanide ions and the Tb III bioconjugate with BSA yielded highly contrasted time-resolved luminescence images of rat brain slices …”

A Gadolinium‐Binding Cyclodecapeptide with a Large High‐Field Relaxivity Involving Second‐Sphere Water

“…10 mm) of complex. Rough estimates of t M can be obtained in favourable cases with somewhat smaller concentrations if the 17 O experiments are very carefully performed [54] with spherical NMR samples in a 10 mm probe of a spectrometer operating at a high frequency (! 500 MHz).…”