  We report a new approach to controllable thermal stimulation of a single
living cell and its compartments. The technique is based on the use of a single
polycrystalline diamond particle containing silicon-vacancy (SiV) color
centers. Due to the presence of amorphous carbon at its intercrystalline
boundaries, such a particle is an efficient light absorber and becomes a local
heat source when illuminated by a laser. Furthermore, the temperature of such a
local heater is tracked by the spectral shift of the zero-phonon line of SiV
centers [2]. Thus, the diamond particle acts simultaneously as a heater and a
thermometer. In the current work, we demonstrate the ability of such a Diamond
Heater-Thermometer (DHT) to locally alter the temperature, one of the numerous
parameters that play a decisive role for the living organisms at the nanoscale.
In particular, we show that the local heating of 11-12 {\deg}C relative to the
ambient temperature (22 {\deg}C) next to individual HeLa cells and neurons,
isolated from the mouse hippocampus, leads to a change in the intracellular
distribution of the concentration of free calcium ions. For individual HeLa
cells, a long-term (about 30 s) increase in the integral intensity of Fluo-4 NW
fluorescence by about three times is observed, which characterizes an increase
in the [Ca2+]cyt concentration of free calcium in the cytoplasm. Heating near
mouse hippocampal neurons also caused a calcium surge - an increase in the
intensity of Fluo-4 NW fluorescence by 30% and a duration of ~0.4 ms.
