Solvatochromic BODIPYs with Polarity-Independent Absorption for Functional Super-resolution Imaging of Live Cell...

Functional super-resolution microscopy (SRM) has recently emerged as a powerful technique for concurrently mapping nanoscale physicochemical properties of the subcellular environment. This is accomplished by capturing both the spatial localization and single-molecule fluorescence spectral shifts of environmentally sensitive fluorescent probes. However, current fluorophore choices for functional SRM are largely limited to Nile Red derivatives, which suffer from several limitations. Here we report two solvatochromic and far-red-emitting fluorophores with polarity-independent absorption specifically tailored for functional SRM, based on a boron dipyrromethene (BODIPY) chromophore. We systematically characterize their photophysical and solvatochromic properties and directly compare their performance to that of Nile Red. A zwitterionic lipid is introduced to the dye to enable transient-binding-based single-molecule switching and to achieve selective targeting of the plasma membrane in live cells. The functional SRM capability of this probe is demonstrated by mapping nanoscale membrane polarity changes under the influence of cholesterol in live U2OS cells with a localization precision of 16-20 nm.