Organic-Inorganic Hybrid Nanoparticles for Tracking the Same Cells Seamlessly at the Cellular, Tissue, and Whole Body Levels.

Techniques to elucidate the kinetics and distribution of the same cells in the whole body and in tissues are necessary for further studies of cancer, immunity, and regenerative medicine. Fluorescent imaging is a powerful technique for visualization of cells. However, current fluorescent probes are applicable in either the ultraviolet (UV)-visible (Vis) region (300-650 nm) or the biological transparency window (BTW, 650-900 nm), but not both. Thus, they cannot serve as fluorescent probes for both in vivo and in vitro imaging, and it is difficult to achieve imaging of the same cells seamlessly from the cellular level to the whole body and tissue levels using currently available fluorescent probes. Accordingly, in this paper, we describe organic-inorganic hybrid nanoparticles (HNPs) that could be used to achieve seamless tracking of the same cells. Within the HNPs, a porphyrin molecule, Vis-fluorophore, was surrounded by a siloxane chain, preventing the aggregation of porphyrin molecules. As a result, the porphyrin fluorescence was not quenched. Furthermore, indocyanine green (ICG), a BTW fluorophore, was localized on the HNP surface, leading to fluorescence resonance energy transfer (FRET) from porphyrin to ICG only near the HNP surface. Through the above structural design, the HNPs acquired both excitation (λ) and emission (λ) wavelengths in the visible region and BTW, respectively, as well as large Stokes shifts. The HNP-labeled immune cells successfully and the labeled cells were separated easily from unlabeled cells by fluorescence-activated cell sorting. The kinetics of the labeled cells in the whole body were revealed by fluorescence imaging within BTW. Furthermore, the distributions of the same labeled cells were elucidated by histological analysis within the UV-vis region. Thus, the HNPs served as fluorescent probes for seamless tracking of the same cells.