Near-Ir Two-Photon Fluorescent Sensor For K\u3csup\u3e+\u3c/sup\u3e Imaging In Live Cells

A new two-photon excited fluorescent K+ sensor is reported. The sensor comprises three moieties, a highly selective K+ chelator as the K+ recognition unit, a boron-dipyrromethene (BODIPY) derivative modified with phenylethynyl groups as the fluorophore, and two polyethylene glycol chains to afford water solubility. The sensor displays very high selectivity (\u3e52-fold) in detecting K+ over other physiological metal cations. Upon binding K+, the sensor switches from nonfluorescent to highly fluorescent, emitting red to near-IR (NIR) fluorescence. The sensor exhibited a good two-photon absorption cross section, 500 GM at 940 nm. Moreover, it is not sensitive to pH in the physiological pH range. Time-dependent cell imaging studies via both one- and two-photon fluorescence microscopy demonstrate that the sensor is suitable for dynamic K+ sensing in living cells