Stimulated emission depletion (STED) microscopy enables ultrastructural imaging of biological samples with high spatiotemporal resolution. STED nanoprobes based on fluorescent organosilica nanohybrids featuring sub-2 nm size and near-unity quantum yield are presented. The spin–orbit coupling (SOC) of heavy-atom-rich organic fluorophores is mitigated through a silane-molecule-mediated condensation/ dehalogenation process, resulting in bright fluorescent organosilica nanohybrids with multiple emitters in one hybrid nanodot. When harnessed as STED nanoprobes, these fluorescent nanohybrids show intense photoluminescence, high biocompatibility, and long-term photostability. Taking advantage of the low-power excitation (0.5 mW), prolonged singlet-state lifetime, and negligible depletion-induced re-excitation, these STED nanohybrids present high depletion efficiency (> 96%), extremely low saturation intensity (0.54 mW, ca.0.188 MWcm@2), and ultra-high lateral resolution (ca. lem/28).
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