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It is crucial for cell physiology to keep the homeostasis of pH, and it is highly demanded yet challenging to develop luminescence resonance energy transfer (LRET)-based near-infrared (NIR) ratiometric luminescent sensor for the detection of pH fluctuation with NIR excitation. As promising energy donors for LRET, upconversion nanoparticles (UCNPs) have been widely used to fabricate nanosensors, but the relatively low LRET efficiency limits their application in bioassay. To improve the LRET efficiency, core/shell/shell structured ß-NaGdF[sub 4]@NaYF[sub 4]:Yb,Tm@NaYF[sub 4] UCNPs were prepared and decorated with hemicyanine dyes as an LRET-based NIR ratiometric luminescent pH fluctuation-nanosensor for the first time. The as-developed nanosensor not only exhibits good antidisturbance ability, but it also can reversibly sense pH and linearly sense pH in a range of 6.0-9.0 and 6.8-9.0 from absorption and upconversion emission spectra, respectively. In addition, the nanosensor displays low dark toxicity under physiological temperature, indicating good biocompatibility. Furthermore, live cell imaging results revealed that the sensor can selectively monitor pH fluctuation via ratiometric upconversion luminescence behavior. [ABSTRACT FROM AUTHOR]

Previous reports of fluorescent sensors for alcohols based on charge-transfer character of their excited state are based on mono-, di-, and tetra-phosphonate cavitands, which are capable of selecting analytes through shape/size selection and various specific H-bonding, CH−π, and cation–dipole interactions. To contrast, color changes based on absorption properties of the ground state are more suitable for direct observation with the naked eye. Three sensitive and selective colorimetric sensors for C1–C4 alcohols have been developed on the basis of alcohol-mediated ground-state intramolecular proton transfer. Reverse proton transfer induced by water achieves a fully reversible reaction. In addition, the solvent color indicates alcohol concentration. [ABSTRACT FROM AUTHOR]

A highly fluorescent chemosensor based on 1,8-naphthyridine with high sensitivity and selectivity toward Ni2+/Cu2+ over other cations both in aqueous solution over a wide pH range (4--10) and in cellular environments was developed. Counteranions such as acetate, sulfate, nitrate, and perchlorate have no influence on the detection of such metal ions. Ethylenediamine showed high selectivity toward the in situ-prepared Cu2+ complex over die Ni2+ complex, which can be applied to distinguish Ni2+ and Cu2+. The Ni2+-induced fluorescence on--off mechanism was revealed to be mediated by intramolecular charge transfer from the metal to the ligand, while that by Cu2+ involves intramolecular charge transfer from the ligand to the metal, as confirmed by picosecond time-resolved fluorescence spectroscopy and time-dependent density functional theory calculations. [ABSTRACT FROM AUTHOR]