For the purpose of live cells imaging, first we evaluated the cytotoxicity by using the standard MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide) assay on Chinese hamster ovary (CHO) cells. The CHO cells were treated with different concentrations of Nuc-DAOTA + for 24 hours at 37 o C (Figure ). The results showed that >90% of the CHO cells stayed viable at 8.2 μM concentrations of Nuc-DAOTA + and an IC50 value was calculated to be 74 μM.