A nanoparticle-based ratiometric and self-calibrated fluorescent thermometer for single living cells.The homeostasis of body temperature and energy balance is one of the major principles in biology.  Nanoscale thermometry of aqueous solutions is a challenging but crucial technique to understand the molecular basis of this essential process.  Here, we developed a ratiometric nanothermometer (RNT) for intracellular temperature measurement in real time.  Both the thermosensitive fluorophore, β-diketonate chelate europium(III) thenoyltrifluoroacetonate, and the thermoinsensitive fluorophore, rhodamine 101, which was used as a self-reference, are embedded in a polymeric particle that protects the fluorophores from intracellular conditions.  As a demonstration of the spot-by-spot intracellular thermometry, we successfully followed the temperature change in individual RNT spots in a single cell together with the Ca(2+) burst induced by the Ca(2+) ionophore ionomycin. 
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