Cell surface imaging and bioorthogonal chemistry

The labelling of the plasma membrane with targeted fluorescent probes offers a convenient and non-invasive means to image the cell membrane and follow morphological changes and dynamics in real-time. However, despite many examples of fluorescent plasma membrane probes, a “universal targeting/anchoring moiety” is still required. In the first research section of my PhD, I report on the development of a small library of stearic acid-based probes, labelled with 6-carboxyfluorescein, via solid-phase synthesis, in which variation in both charge and hydrophobicity were explored. An optimal probe was discovered that carried both a positively charged amino group and a stearic acid tail that exhibited intense plasma membrane brightness and robust retention. In the second section of my PhD thesis, I investigated a light-driven, reversible addition−fragmentation chain-transfer (photo-RAFT) polymerisation with a newly developed fluorophore-conjugated RAFT agent, containing a BODIPY dye attached to a thiocarbonylthio group. This new RAFT agent enabled light-controlled (470 nm) “on/off” polymerisation, producing well-defined polymers, with excellent photostability. It provides an expedient route to homogeneous fluorescently-labelled polymers. In the third part of my PhD thesis, I discovered amphiphilic polymer-based fluorescent probes which showed long-term plasma membrane binding, and that allowed imaging and simultaneous functionalisation of the cell surface with azides, as shown by fluorophore attachment via cycloaddition chemistry. The polymer structure was optimised using a library approach