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A novel Zn2+ fluorescent probe Nʹ-((4′-(diphenylamino)-4-hydroxy-[1,1′-biphenyl]-3-yl)methylene)-2-hydroxybenzohydrazide (TPA-HPH) with a larger Stokes shift (210 nm) was designed and synthesized, which was seen to be highly selective and sensitive to Zn2+ ion over other metal ions in the system of MeCN:H2O (V/V = 6:4, pH = 7.0). Meanwhile, it was observed that the TPA-HPH solution changed from colorless to yellow by "naked eye" when Zn2+ was added. Under optimized conditions, the fluorescence intensity of the probe showed a good linear relationship with Zn2+ ion concentration in the range of 0–10 μM with a low detection limit of 7.3 × 10−10 M. The fluorescent mechanism was proposed. Most importantly, TPA-HPH could realize on-site monitor and live cell imaging for Zn2+ ion. [ABSTRACT FROM AUTHOR]

Glutathione (GSH) plays a critical role in maintaining oxidation-reduction homeostasis in biological systems. Considering the detection of GSH by fluorescence sensors is limited by either the short wavelength emission or the poor photostability, a highly stable colorimetric and ratiometric NIR fluorescent sensor (DCM-S) for GSH detection has been constructed on the basis of dicyanomethylene-4 H-pyran (DCM) chromophore. The specific disulfide bond is incorporated via a carbamate linker as the GSH responsive group, which simultaneously blue-shifts and quenches the fluorescence. Upon addition of GSH, DCM-S exhibits outstanding colorimetric (from yellow to red) and ratiometric fluorescent response with the 6-fold enhancement of NIR fluorescence at 665 nm in quantum yield. More importantly, the GSH-treated DCM-S (DCM-NH actually) possesses 20-fold longer fluorescence half-life period as well as much better photostability than the FDA-approved ICG. Finally, the ratiometric detection of GSH is also successfully operated in the living cell imaging, exhibiting NIR fluorescence and large Stokes shift (215 nm) with nearly no background fluorescence interference. As a consequence, DCM-S can be utilized as colorimetric and ratiometric NIR fluorescent sensor for GSH, with a great potential in the development of GSH-induced drug delivery system. [ABSTRACT FROM AUTHOR]

Three tricarbocyanine dyes (IR-897, IR-877, and IR-925) with different thiourea substituents that function as dosimeter units through specific Hg(2+)-induced desulfurization have been demonstrated in a fast indicator paper for Hg(2+) and MeHg(+) ions. In comparison with available Hg(2+)-selective chemodosimeters, IR-897 and IR-877 show several advantages, such as convenient synthesis, very long wavelengths falling in the near-infrared (NIR) region (650-900 nm) with high molar extinction coefficients, a ratiometric response, and quite low disturbance with Ag(+) and Cu(2+) ions. They exhibit large redshifts, which result in a clear color change from deep blue to pea green that can be easily monitored by the naked eye for a convenient indicator paper. In emission spectra, they display a characteristic turn-off mode at 780 nm and turn-on mode at 830 nm with titration of Hg(2+) ions. Remarkably, the signal/noise (S/N) ratio with other thiophilic metal ions (Ag(+) and Cu(2+)) is greatly enhanced with ratiometric measurement of two channels: excitation spectra mode (I(810 nm)/I(670 nm), monitored at 830 nm) and emission spectra mode (I(830 nm)/I(780 nm), isosbestic absorption point at 730 nm as excitation). The distinct response is dependent upon the electron-donating effect of the thiourea substituents; that is, the stronger the electron-donating capability of the thiourea substituents, the faster the Hg(2+)-promoted cyclization. Additionally, experiments with living SW1116 cells show that these three tricarbocyanine dyes with low toxicity can exhibit special characteristics that are favorable for visualizing intracellular Hg(2+) and MeHg(+) ions in biological systems, including excellent membrane permeability, minimal interfering absorption and fluorescence from biological samples, low scattering, and deep penetration into tissues.