Tb‐doped La0.9Tb0.1F3 nanoparticles were prepared by a simple and reproducible microwave‐assisted synthetic protocol in water. The nanoparticles were characterized by XRD, TEM, dynamic light scattering and inductively coupled plasma atomic emission spectroscopy elemental analysis. Eleven ligands with varying coordination and photosensitizing abilities were designed to bind at the surface of the Tb‐doped nanoparticles. The photosensitizing behavior was monitored by electronic absorption spectroscopy and steady‐state and time‐resolved emission spectroscopy. The two most effective photosensitizing ligands were used to isolate and purify the capped nanoparticles. The composition and spectroscopic properties of these nanoparticles were measured, which revealed either 2660 and 5240 ligands per nanoparticle, molar absorptivities of 7.6×106 and 1.6×107 m−1 cm−1 and luminescence quantum yields of 0.29 and 0.13 in water, respectively. These data correspond to exceptional brightness values of 2.2×106 and 2.1×106 m−1 cm−1, respectively. The as‐prepared nanoparticles were imaged in HeLa cells by fluorescence microscopy, which showed their specific localization in lysosomes.
Fluorescent nanoparticles (NPs) have become irreplaceable tools for advanced cellular and subcellular imaging. While very bright NPs require excitation with UV or visible light, which can create strong autofluorescence of biological components, NIR-excitable NPs without autofluorescence issues exhibit much lower brightness. Here, we show the application of a new type of surface-photosensitized terbium NPs (Tb-NPs) for autofluorescence-free intracellular imaging in live HeLa cells. The combination of exceptionally high brightness, high photostability, and long photoluminecence (PL) lifetimes for highly efficient suppression of the short-lived autofluorescence allowed for time-gated PL imaging of intracellular vesicles over 72 h without toxicity and at extremely low Tb-NP concentrations down to 12 pM. Detection of highly resolved long-lifetime (ms) PL decay curves from small (∼10 μm) areas within single cells within a few seconds emphasized the unprecedented photophysical properties of Tb-NPs for live-cell imaging that extend well beyond currently available nanometric imaging agents.
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