Quantum dots based probes conjugated to annexin V for photostable apoptosis detection and imaging.

Quantum dots (Qdots) are nanoparticles exhibiting fluorescent properties that can be used for cell staining. We present here the development of quantum dots conjugated to Annexin V for specific targeting of apoptotic cells, for both apoptosis detection and staining of apoptotic "living" cells. For that purpose, Qdots Streptavidin Conjugates are coupled to biotinylated Annexin V, a 35-kDa protein which specifically recognizes and binds to phosphatidylserine (PS) moieties present on the outer membrane of apoptotic cells and not on healthy or necrotic cells. By using Annexin V, our Qdots probes are made specific for apoptotic cells. Staining of apoptotic cells was checked using fluorescence and confocal microscopy techniques and nonfixed cells. It is shown here that Qdots are insensitive to bleaching after prolonged exposure as opposed to organic dyes. This makes Qdots excellent candidates to continuously follow fast changes occurring at the membrane of apoptotic cells and facilitates time-lapse imaging as they alleviate any bleaching issue.