Germanium-vacancy centers in detonation nanodiamond for all-optical nanoscale thermometry

Nanodiamonds with group-IV color centers, such as silicon-vacancy centers and germanium-vacancy (GeV) centers, exhibit excellent properties, including a sharp and stable zero-phonon line, surface functionalization, and low cytotoxicity. Because the line peak wavelength shifts linearly with the temperature under ambient conditions, the nanodiamonds are promising candidates for all-optical nanoscale thermometry inside a living cell. However, the particles used for temperature measurements have been reported to be larger than a few hundred nanometers. Here, we report temperature sensing using GeV detonation nanodiamonds. The GeV nanodiamonds have a mean particle size of 20 nm. These are the smallest particles among GeV-based particles used in thermometry. The sensitivity of the single GeV centers in the detonation nanodiamond is estimated to be almost consistent with the reported ones of the single GeV centers in bulk diamonds, which can potentially reach sub-kelvin temperature accuracy. The GeV detonation nanodiamonds should function as good photoluminescence probes and intracellular temperature sensors.