Fluorescent labeling of biomolecules (immunoassays, biochips...) is one of the leading applications of semiconductor nanocrystals. They combine a tunable emission wavelength with a large absorption spectrum. Their improved stability against photobleaching compared to organic dyes represents another advantage. We are working on new methods for the hydrosolubilisation of nanocrystals and their grafting on proteins or oligonucleotides, and on the use of QDs in FRET-based immunoassays. In recent years also nanotoxicological studies both in vitro and in vivo have been undertaken, in particular on novel types of QDs like InP.

 
Fluorescence microscopy images of agarose beads (mean size: 50µm), labeled with biotinylated nanocrystals (top row) and with biotinylated R-Phycoerythrin (bottom row). The photos are taken at the specified time intervals under continuous irradiation with a mercury lamp. While the fluorescence of the Phycoerythrin labeled beads is practically extinguished after 15 minutes, the emission of the nanocrystal labeled ones can still be detected after 8 hours, demonstrating a significantly higher photostability.
Details

CuInS₂/ZnS QDs under room light (left), UV light (middle), and bio-distribution (right) revealed by fluorescence reflectance imaging.

InP/ZnS QDs showing long-term (> 3 months) colloidal stability and retaining > 90% of the initial fluorescence quantum yield after aqueous phase transfer with bifunctional thiols under optimized conditions. These comprise the precise adjusting of pH value of the aqueous phase containing the new ligand and the use of an appropriate reducing agent for disulfide bonds, such as tris(2-carboxyethyl)phosphine, TCEP.

 Main collaborators:
 I. Texier and coll. (CEA Grenoble, DRT/LETI/DTBS)
 M. Dahan and coll. (Institut Curie, Paris)
 M. De Waard (INSERM Grenoble)
 D. Imbert, M. Mazzanti, M. Carriere (CEA Grenoble, INAC/SyMMES)
C. Tortiglione (CNR Pozzuoli)
 L. Charbonniere (IPHC Strasbourg)
N. Hildebrandt (IEF Orsay)

Our current research focuses on the development of cadmium-free fluorescent probes for in vivo and in vitro applications.

Funding from the European Union FP6/FP7 (POC4LIFE), from the French Research Agency ANR (SYNERGIE, NIRA, NANOFRET, NEUTRINOS) and from CEA is acknowledged.