Highly Selective, Red Emitting BODIPY-Based Fluorescent Indicators for Intracellular Mg Imaging.

Most fluorescent indicators for Mg suffer from poor selectivity against other divalent cations, especially Ca, thus do not provide reliable information on cellular Mg concentrations in processes in which such metals are involved. We report a new set of highly selective fluorescent indicators based on alkoxystyryl-functionalized BODIPY fluorophores decorated with a 4-oxo-4-quinolizine-3-carboxylic acid metal binding moiety. The new sensors, and , display absorption and emission maxima above 600 nm, with a 29-fold fluorescence enhancement and good quantum yields (Φ > 0.3) upon coordination of Mg in aqueous buffer. Fluorescence response to Mg is not affected by the presence of competing divalent cations typically present in the cellular milieu, and displays minimal pH dependence in the physiologically relevant range. The choice of alkoxy groups decorating the styryl BODIPY core does not influence the basic photophysical and metal binding properties of the compounds, but has a marked effect on their intracellular retention and thus in their applicability for detection of cellular Mg by fluorescence imaging. In particular, we demonstrate the utility of a triethyleneglycol (TEG) functionalization tactic that endows with superior cellular retention in live cells by reducing active extrusion through organic anion transporters, which are thought to cause fast leakage of typical anionic dyes. With enhanced retention and excellent photophysical properties, can be applied in the detection of cellular Mg influx without interference of high concentrations of Ca akin to those involved in signaling.