Time-resolved luminescence microscopy of bimetallic lanthanide helicates in living cells

The cellular uptake mechanism and intracellular distribution of emissive lanthanide helicates have been elucidated by time-resolved luminescence microscopy (TRLM). The helicates are non-cytotoxic and taken up by normal (HaCat) and cancer (HeLa, MCF-7) cells by endocytosis and show a late endosomal-lysosomal cellular distribution. The lysosomes predominantly localize around the nucleus and co-localize with the endoplasmatic reticulum. The egress is slow and limited, around 30% after 24 h. The first bright luminescent images can be observed with an external concentration gradient of 5 mu M of the Eu-III helicate [Q = 0.21, tau = 2.43 ms], compared to > 10 mM when using conventional luminescence microscopy. Furthermore, multiplex labeling could be achieved with the Tb-III [Q = 0.11, tau = 0.65 ms], and Sm-III [Q = 0.0038, tau = 0.030 ms] analogues.