Spatiotemporally Mapping Thermodynamics of Lysosomes and Mitochondria using Cascade Organelle-Targeting Upconversion Nanoparticles

The intracellular metabolism of organelles, like lysosomes and mitochondria, are highly coordinated spatiotemporally and functionally. The activities of lysosomal enzymes significantly rely on the cytoplasmic temperature, and heat is constantly released by mitochondria as the byproduct of ATP generation during active metabolism. Here, we develop temperature-sensitive LysoDots and MitoDots to monitor the in situ thermodynamics of lysosomes and mitochondria. The design is based on upconversion nanoparticles (UCNPs) with high-density surface modifications to achieve the exceptionally high sensitivity of 2.7% K-1 and accuracy of 0.8 K for nanothermometry to be used in living cells. We show the measurement is independent of the intracellular ion concentrations- and pH values. With Ca2+ ion shock, the temperatures of both lysosomes and mitochondria increased by 2[~]4 {degrees}C. Intriguingly, with Chloroquine treatment, the lysosomal temperature was observed to decrease by up to [~]3 {degrees}C, while mitochondria remained relatively stable. Lastly, with oxidative phosphorylation inhibitor treatment, we observed a 3[~]7 {degrees}C thermal increase and transition from mitochondria to lysosomes. These observations indicate different metabolic pathways and thermal transitions between lysosomes and mitochondria inside HeLa cells. The nanothermometry probes provide a powerful tool for multi-modality functional imaging of subcellular organelles and interactions with high spatial, temporal and thermal dynamics resolutions. Graphical AbstractCascade organelle-targeted nano-thermometers based on upconversion LysoDots and MitoDots. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=159 SRC="FIGDIR/small/480800v1_ufig1.gif" ALT="Figure 1"> View larger version (93K): org.highwire.dtl.DTLVardef@13b8124org.highwire.dtl.DTLVardef@19b78a8org.highwire.dtl.DTLVardef@e866corg.highwire.dtl.DTLVardef@19b51d3_HPS_FORMAT_FIGEXP M_FIG C_FIG