An Organometallic Ir(III) Molecular Probe for Imaging Microtubules in Fluorescence and Electron Microscopy

Microtubules are a critical component of the cell cytoskeleton and an important actor in cell mitosis and adhesion. Yet their imaging has been limited by the lack of effective probes. Fluorescent imaging can be performed using either taxol derivates, immunoglobins, or genetically encoded fluorescent proteins. These approaches however tend to hinder microtubulin functionality and they do not bestow any contrast in electron microscopy. Here we present a cyclometalated Iridium(III) complex that bind to microtubulin and allow both fluorescent and electron microscopy imaging. The complex displays a light switch phenomena coupled with strong luminescence intensity upon tubulin protein binding without interfering into cell proliferation. Furthermore, the application of super resolution imaging of microtubule ultrastructure within brain neuron network under stimulated emission depletion (STED) microscopy was successfully demonstrated. More importantly, the Ir-Tub showed its capability to display microtubule structure under protein monomeric level by means of energy-filtered transmission electron microscopy (EF-TEM). This innovative complex sheds light on the visualization and modeling of precise microtubule structure, aiding a much better understanding of correlated cellular mechanisms and ultimately associated diseases.