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.

Precise in vivo tracking of hydrogen peroxide is still challenging due to its dynamic complexity and intrinsic background interference. Herein, we describe a rational design strategy to construct asymmetric aza-boron-dipyrromethane derivative (BODIPY)-based ratiometric probes for in vivo tracking H 2 O 2 , which are composed of a near-infrared aza-BODIPY core, active targeting group, and H 2 O 2 -specific recognition unit. We take advantage of two terminal functionalized conjunctions in the bis-condensed aza-BODIPY by rationally introducing carbonyl group as an electrondeficiency linker for regulating intramolecular charge transfer-induced wavelength shift and by attaching hydrophilic polyethylene glycol-biotin segment as the active targeting moiety. The probe BP 5 -NB-OB features several striking characteristics: (i) ratiometric near infrared response in both absorption and emission spectra; (ii) active targeting ability (biotin receptor-mediated endocytosis) with excellent biocompatibility; and (iii) in vivo tracking of endogenous H 2 O 2 . It was demonstrated that the probe BP 5 -NB-OB was successfully utilized for tracking endogenous H 2 O 2 in living cells and tumorbearing mice, providing opportunities to insight into H 2 O 2 related diseases for clinical application.