POLYMETALLIC LUMINESCENT DENDRIMER-LANTHANIDE COMPLEXES

The medical and biological fields of today have high demands for luminescent molecules for fluorescence microscopy and imagery that can report biological activities or would allow the quantification of in vivo biologically relevant molecules or ions. Fluorescence microscopy is a principal technique due to its high sensitivity and versatility.This work explores a new concept to optimize the intensity of luminescent complexes by maximizing the number of lanthanide cations and the number of sensitizing groups per discrete molecule of complex. PAMAM (polyamidoamine) dendrimer ligands have been chosen as the coordinating unit for the formation of these polymetallic lanthanide complexes. Generation 3 dendrimer possess 60 amide groups, i.e. 60 oxygen groups to bind 7-8 lanthanide cations with a coordination number of 9. In addition, the globular structure of the dendrimer is expected to shield the lanthanide cations from molecules (such as water) that can diminish the luminescence of the complex through non-radiative deactivation. Another advantage of this strategy is that sensitizers do not need to be directly bound to the metal ion, allowing for a broader choice of lanthanide sensitizers. A family of naphthalimide groups was chosen as sensitizers because of the high population of their triplet state, a desirable property for the ligand to lanthanide energy transfer, and their sensitivity to oxygen molecules. Preliminary experiments have demonstrated that each of the dendrimer-naphthalimide ligand is able to coordinate eight Ln3+ cations. These ligands are able to sensitize several visible and NIR emitting lanthanides.The luminescent neodymium complexes were injected into the cells and the emission intensity was monitored through near-infrared fluorescence microscopy. The fluorescence intensity was proportional to the concentration of oxygen present in the cell. The decrease of oxygen concentration from 21% to 1.5% induced an increase of the luminescence signal of 60%. These preliminary experiments are the first examples of a luminescent lanthanide complex emitting in the near-infrared domain used for fluorescence microscopy. It demonstrates that the complex used is luminescent and stable enough to be used as a reporter in physiological conditions