Table 2.

Current issues in luminescence nanothermometry

Category	Description	Comments
Validity of temperature in luminescence nanothermometry	• In aqueous conditions and luminescent temperature probes, the concept of temperature is valid even on a scale of 10 nm. • Temperature fluctuations can be on the order of 1 K at 10-nm scale with a characteristic correlation time on the order of 0.1 ns.	• The fluctuations can be averaged out in most of the current luminescence thermometry and be reduced.
The 105 gap issue	• Amplitude of temperature increase calculated using parameters well identified is unable to explain values determined in measurements.	• Non-luminescent thermal probes also report temperature increases in individual cells. • Thermal conductivity of a single lipid bilayer experimentally determined was about three times smaller than that of water. • Calculations including boundary heat resistance problem expect the average thermal conductivity in cells up to six times smaller than that in water. • This issue is still an open question.