A Bioresponsive Near-Infrared Fluorescent Probe for Facile and Persistent Live-Cell Tracking

Molecular imaging significantly transforms the field of biomedical science and facilitates the visualization, characterization, and quantification of biologic processes. However, it is still challenging to monitor cell localization in vivo, which is essential to the study of tumor metastasis and in the development of cell-based therapies. While most conventional small-molecule fluorescent probes cannot afford durable cell labeling, transfection of cells with fluorescent proteins is limited by their fixed fluorescence, poor tissue penetration, and interference of autofluorescence background. Here, a bioresponsive near-infrared fluorescent probe is reported as facile and reliable tool for real-time cell tracking in vivo. The design of this probe relies on a new phenomenon observed upon fluorobenzene-conjugated fluorescent dyes, which can form complexes with cytosolic glutathione and actively translocates to lysosomes, exhibiting enhanced and stable cell labeling. Fluorobenzene-coupled hemicyanine, a near-infrared fluorophore manifests to efficiently staining tumor cells without affecting their invasive property and enables persistent monitoring of cell migration in metastatic tumor murine models at high resolution for one week. The method of fluorobenzene functionalization also provides a simple and universal "add-on" strategy to render ordinary fluorescent probes suitable for long-term live-cell tracking, for which currently there is a deficit of suitable molecular tools.