For FLIM and time-gated imaging staining method included 3T3 cells seeded in coverslip dishes were incubated with MitoTracker Red CM-H2XRos in 1:1000 in normal medium for 30 min. After 15 minutes the Nuc-DAOTA + was added in a final concentration of 75 μM and left to stain along with the MitoTracker. Then the medium was aspired and cells were briefly washed in PBS before being fixed in 2% PFA/PBS for 10 minutes.