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

Abstract

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 μM of the Eu^III helicate [Q = 0.21, τ = 2.43 ms], compared to >10 μM when using conventional luminescence microscopy. Furthermore, multiplex labeling could be achieved with the Tb^III [Q = 0.11, τ = 0.65 ms], and Sm^III [Q = 0.0038, τ = 0.030 ms] analogues.