Rhodamine B isothiocyanate doped silica-coated fluorescent nanoparticles (RBITC-DSFNPs)-based bioprobes conjugated to Annexin V for apoptosis detection and imaging.

We report here a novel bioprobe based on Rhodamine B isothiocyanate doped silica-coated fluorescent nanoparticles (RBITC-DSFNPs) for early-stage apoptosis detection and imaging. RBITC-DSFNPs were constructed by synchronous hydrolysis of APTES-RBITC and tetraethoxysilane in water-in-oil microemulsion, and the bioprobes were prepared through modifying Annexin V with RBITC-DSFNPs. The characterization of RBITC-DSFNPs and the bioprobes' application for apoptosis detection and imaging were investigated. It was demonstrated that RBITC-DSFNPs are uniform and possess excellent photostability. The bioprobes could specifically recognize early-stage apoptotic cells through the binding between Annexin V and phosphatidylserine (the externalization of which from the inner to the outer membrane is an early and major event in the apoptotic process) on the outer membrane of apoptotic cells. Moreover, the RBITC-DSFNPs labeling method was also used to monitor the increase of the number of early-stage apoptotic cells along with the extended induction time. Compared with the conventional fluorochrome such as Cy3-labeled Annexin V for staining apoptotic cells, the RBITC-DSFNPs labeling method possesses much better photostability, which offers a promising approach for tumor-related research.