An Iridium (III) complex revealing cytoskeleton nanostructures under super-resolution nanoscopy and liquid-phase electron microscopy

Live cell actin visualization is fundamental for exploring cellular motility, cytokinesis, intracellular transport, and other correlated functions. The current imaging techniques that allow imaging of actin in its native environment are optical and electron microscopy. Such imaging techniques offer high enough resolution to investigate the ultrastructure of actin however they come at the expense of actin integrity. Inspired by the lack of suitable probes that preserve actin's integrity, we designed a cyclometalated Ir (III) complex that interacts with live cells and displays light switch behaviour upon specific actin binding. The exceptional photophysical properties of the proposed probe allow unprecedented resolution of cytoskeleton ultrastructures under stimulated emission depletion (STED) super-resolution nanoscopy. Moreover, the Ir complex enables the capability of visualizing actin polymers and periodicity under correlative light electron microscopy (CLEM) and liquid-phase electron microscopy (LPEM) at ∼ 8 nm resolution.