It is difficult to overstate the physiological importance of potassium for life as its indispensable roles in a variety of biological processes are widely known. As a result, efficient methods for determining physiological levels of potassium are of paramount importance. Despite this, relatively few K+ fluorescence sensors have been reported, with only one being commercially available. A new two-photon excited fluorescent K+ sensor is reported. The sensor is comprised of 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 (<52-fold) in detecting K+ over other physiological metal cations. Upon binding K+, the sensor switches from non-fluorescent 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.
A new mitochondrial targeting fluorescent probe is designed, synthesized, characterized, and investigated. The probe is composed of three moieties, a BODIPY platform working as the fluorophore, two triphenylphosphonium (TPP) groups serving as mitochondrial targeting moiety, and two long highly hydrophilic polyethylene glycol (PEG) chains to increase its water solubility and reduce its cytotoxicity. As a mitochondria-selective fluorescent probe, the probe exhibits a series of desirable advantages compared with other reported fluorescent mitochondrial probes. It is readily soluble in aqueous media and emits very strong fluorescence. Photophysical determination experiments show that the photophysical properties of the probe are independent of solvent polarity and it has high quantum yield in various solvents examined. The probe also has good photostability and pH insensitivity over a broad pH range. Results obtained from cell viability tests indicate that the cytotoxicity of the probe is very low. Confocal fluorescence microscopy colocalization experiments reveal that this probe possesses excellent mitochondrial targeting ability and it is suitable for imaging mitochondria in living cells.
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