Development of a time-resolved fluorometric detection system using diffusion-enhanced energy transfer

Facile synthesis of a class of aminochromene–aniliniumion conjugated far-red to near-infrared fluorescent dyes for bioimaging

An innovative class of aminochromene–aniliniumion conjugated far-red to near-infrared dyes, namely ACA, was developed.

A Broad G Protein-Coupled Receptor Internalization Assay that Combines SNAP-Tag Labeling, Diffusion-Enhanced Resonance Energy Transfer, and a Highly Emissive Terbium Cryptate

Although G protein-coupled receptor (GPCR) internalization has long been considered as a major aspect of the desensitization process that tunes ligand responsiveness, internalization is also involved in receptor resensitization and signaling, as well as the ligand scavenging function of some atypical receptors. Internalization thus contributes to the diversity of GPCR-dependent signaling, and its dynamics and quantification in living cells has generated considerable interest. We developed a robust and sensitive assay to follow and quantify ligand-induced and constitutive-induced GPCR internalization but also receptor recycling in living cells. This assay is based on diffusion-enhanced resonance energy transfer (DERET) between cell surface GPCRs labeled with a luminescent terbium cryptate donor and a fluorescein acceptor present in the culture medium. GPCR internalization results in a quantifiable reduction of energy transfer. This method yields a high signal-to-noise ratio due to time-resolved measurements. For various GPCRs belonging to different classes, we demonstrated that constitutive and ligand-induced internalization could be monitored as a function of time and ligand concentration, thus allowing accurate quantitative determination of kinetics of receptor internalization but also half-maximal effective or inhibitory concentrations of compounds. In addition to its selectivity and sensitivity, we provided evidence that DERET-based internalization assay is particularly suitable for characterizing biased ligands. Furthermore, the determination of a Z'-factor value of 0.45 indicates the quality and suitability of DERET-based internalization assay for high-throughput screening (HTS) of compounds that may modulate GPCRs internalization.

Synthesis and characterization of coumarin-based europium complexes and luminescence measurements in aqueous media

A series of new ligands suitable for the formation of luminescent lanthanide complexes in water is described. The chelates are designed for analyte labeling and play the role of fluorescent donor in homogeneous time-resolved fluorescence assays using LEDs as a light source for excitation at 370 nm. Ligands are constructed from a coumarin nucleus, for lanthanide sensitization, and different aminomethylenecarboxy moieties are introduced in positions 7 and 5, 6, or 8 of the sensitizer. A reactive spacer arm under biocompatible conditions (maleimide, azide) is introduced at position 3 for ultimate bioconjugation purposes. The synthesis and characterization of the ligands are described, together with the preparation of their corresponding europium complexes. Photophysical properties of the complexes are investigated in water by means of UV-vis and luminescence spectroscopy.

[Development and biological applications of various bioimaging probes]

Fluorescence imaging is the most powerful technique currently available for continuous observation of dynamic intracellular processes in living cells. However, only a very limited range of biomolecules can be visualized because of the lack of flexible design strategies for fluorescence probes. In our laboratory, it was elucidated that fluorescein which has been widely employed as a core of fluorescence probes could be understood as a directly linked electron donor/fluorophore acceptor system. Fluorescence properties of fluorescein derivatives could be easily anticipated and modulated by controlling the rate of photoinduced electron transfer (PeT) from the donor moiety to the xanthene fluorophore. Further, we found that the opposite direction of PeT from the singlet excited fluorophore to the electron acceptor moiety could be occurred. More than twenty probes for imaging of nitric oxide, beta-galactosidase, highly reactive oxygen species, zinc ion et al. have been developed according to precise and rational design strategies based on PeT mechanism.