Intracellular Subdegree Temperature Sensing and Dynamics by Thermoresponsive Silver Nanoclusters as Molecular Probes

Reported herein are long-lived, red-luminescent silver nanoclusters (AgNCs) protected by the small-molecule ligand thiolactic acid, which exhibit exceptional stability (shelf life exceeding three years, photostability ∼100%), water-solubility, and high biocompatibility, making them suitable for diverse applications such as sensing and live-cell imaging. The AgNCs display extremely sensitive (>2% K^-1) temperature-dependent luminescence, monitored by a dual approach of changes in photoluminescence intensity and excited-state lifetime, enabling precise local thermal environment monitoring with a very high-resolution temperature sensing down to subdegree levels (<0.5 K). MTT assay, confocal fluorescence imaging, and fluorescence lifetime imaging microscopy (FLIM) analysis of mammalian cells suggest that the non-cytotoxic AgNCs specifically stain lysosomes in live cells, functioning as an organelle-specific biomarker and providing critical insights into lysosomal dynamics and intracellular temperature fluctuations. The unique properties of these AgNCs, corroborated by detailed mechanistic studies, open new avenues for studying nanoscale subcellular physiology and developing temperature-sensitive diagnostics and preservation strategies.