The photo-bleaching experiment was conducted by using equal concentrations of both Nuc-DAOTA + and a reference nucleus-stain, propidium iodide suitable for fixed cells. Both dyes were used to stain fixed 3T3 cells in three separate experiments and the average intensity was calculated for each experiment from three nuclei. The photobleaching results showed that Nuc-DAOTA + performed equally competent for photostability during whole experiment with slight initial intensity drop (Figure , ESI).