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Infrared probes for bioanalysis and subcellular imaging

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Organometallic complexes including carbonyl ligands (CO) display unique spectroscopic features owing to the presence of characteristic and intense bands in the mid-IR range (2000 cm-1 region), where biomolecules do not absorb. These bands originate from the stretching vibration modes of the C-O bonds and their number and position depend on the metal and the space group of the complex. This spectral property led to the development of a new non isotopic immunoassay metho called CMIA associating metal carbonyl (MCO) complexes and IR spectroscopy.
To extend the usefulness of MCO entities as bioprobes, we also focussed our studies on the labeling of antibodies. The purpose was to introduce as many MCO groups as possible without compromising the recognition ability of the antibodies for their antigens. To do that, Fe(CO)2 entities were conjugated to generation 4 PAMAM dendrimer via its terminal amino groups, then the modified dendrimer was coupled to an antibody (IgG) via its polysaccharide moieties.
Recent progresses have been witnessed in IR instrumentation for microscopic scale analysis (synchrotron beam IR spectromicroscopy, AFM-IR) For instance, chemical imaging of a MDA-MB-231 breast cancer cell incubated with a mestranol derivative carrying a Re(CO)3 entity (25 µM, 1 h) was achieved with a IR microscope using a multi-beam IR source for a synchrotron and a focal planar array detector (IRENI). ; mapping of the MCO probe was established on the basis of its absorption at 1915 and 2025 cm-1 at a resolution in the µm range.

Imaging of mestranol-Re(CO)3 within a MCF-7 breast cancer cell was also achieved at higher resolution by AFM-IR which showed preferential accumulation of this molecule in the Golgi apparatus.

A. Vessières, Metal carbonyl tracers and the ferrocifen family, two facets of bioorganometallic chemistry. J. Organomet. Chem. 2013, 734, 3-16. DOI : 10.1016/j.jorganchem.2012.12.020
S. Clède, F. Lambert, C. Sandt, S. Kascakova, M. Unger, E. Harte, M-A. Plamont, R. Saint-Fort, A. Deniset-Besseau, Z. Gueroui, A. Vessières, C. Policar, Analyst 2013, 138, 5627-5638. DOI : 10.1039/c3an00807j