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Abstract Hydrogen polysulfides (H 2 S n , n > 1) influence a variety of important biological functions and activities associated with hydrogen sulfide (H 2 S). The development of probes for rapid, selective, and sensitive detection of H 2 S n still remains a great challenge. Lysosome plays crucial roles in various physiological processes among living cells, which arouse high interest in detecting endogenous lysosome-targetable H 2 S n. To the best of our knowledge, there is no lysosome-targetable probe for H 2 S n has been reported. In this work, a new lysosome-targetable probe NIPY NF , based on the scaffold of imidazo [1,5-]pyridine, with a large Stokes shift (215 nm), low detection limit (84 nM), fast response time (6 min) and low cytotoxicity was designed and synthesized. Furthermore, NIPY NF was successfully applied into the cell imaging for detection of endogenous lysosome-targetable H 2 S n. Graphical abstract Image 1 Highlights • A novel lysosome-targetable probe NIPY NF was reported. • NIPY NF could discriminate H 2 S n over other analytes with high sensitivity, a low detection limit and a large Stokes shift. • NIPY NF could detect the endogenous H 2 S n in lysosome of living cells. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) is one of the endogenous regulators of many physiological processes. NIPY-OH based on an imidazo[1,5-α]pyridine has a large Stokes shift, high photostability with green-emission, relatively high fluorescence quantum yield. NIPY-OH could serve as an excellent candidate for the design of fluorescent probes. However, the reported probes cannot sufficiently take advantage of the optical properties of NIPY-OH due to the water-soluble problem. Herein, a new fluorescent probe NIPY-PBA, based on NIPY-OH, was designed for the detection of hydrogen sulfide. By rational design, compared with other probes, we successfully obtained the probe with higher sensitivity (limit of detection = 43 nM) and shorter response time (1.5 minutes) due to better water solubility. NIPY-PBA maintained the excellent optical properties of a 230-fold fluorescence enhancement with a large Stokes shift (208 nm) at the same time. Furthermore, NIPY-PBA was applied for the fluorescence imaging of H2S in living cells with low cytotoxicity, indicating NIPY-PBA has great potential to monitor H2S in biological systems. [ABSTRACT FROM AUTHOR]

Two new β-diketone-boron difluoride based near-infrared fluorescent probes 1 and 2 which exhibit polarity sensitivity have been designed and synthesized. Probes 1 and 2 are composed of a β-diketone-boron difluoride moiety as an acceptor unit, and a diethylamino group and a phenolic hydroxyl group as donor units. The long conjugate structures form a "donor–acceptor–donor" configuration, induce intramolecular charge transfer (ICT), and confer near-infrared fluorescence emission and excellent polarity sensitivity. The photophysical properties of these two probes were investigated in detail. Experimental data demonstrated that as the environmental polarity decreased, the fluorescence intensity of the probes increased obviously, accompanied by a blue-shift of the maximum emission wavelength. In addition, these two probes were photostable and solely sensitive to polarity without interference from viscosity, pH and common active species. Theoretical calculations indicated that probes 1 and 2 displayed lower energy gaps and faster non-radiative decay in polar solvents. Furthermore, probes 1 and 2 were utilized to quantitatively detect the polarity of a binary mixture through the satisfactory linear relationship between the fluorescence emission intensity ratios and the orientation polarizability of the mixed solvent. Additionally, probe 1 was successfully utilized to visualize the polarity distribution of live cells. Both of these probes are perfect candidates for studying polarity in vitro and even in live systems. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S), an endogenous gaseous signalling molecule, has attracted attention in biochemical research. The detection of H2S in living systems is essential for studying its functions. Although a variety of probes have been reported for the detection of cellular H2S, the development of rapid, highly selective and sensitive near-infrared (NIR) probes for in vivo detection of H2S still remains a challenging target. Herein we synthesized a near-infrared fluorescent probe Cy-PBA, with good selectivity, high sensitivity (limit of detection = 21 nM) and rapid response time (＜1.5 minutes). Importantly, Cy-PBA was successfully applied for fluorescence imaging of H2S in living cells, mice and tissues with low cytotoxicity, indicating that it owns broad application prospects in the detection of H2S in biological samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new dye was synthesized and the spectral properties were studied. • The dye showed good spectral properties and was used to detect SO 2 derivatives. • The reactivity of the probe could be regulated by the thiomorpholine group. A new coumarin-hemicyanine dye was synthesized and used as a ratiometric fluorescent probe for SO 2 derivatives (HSO 3 -/SO 3 2-). The probe showed deep-red fluorescence, ratiometric response, good selectivity, low detection limit and well-separated emission bands. Moreover, the probe was mitochondria-targeted, and was applied to image SO 2 derivatives in living cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new pH sensitive fluorescent probe termed NAP-MDA is developed. • NAP-MDA possesses an excellent linear dependence with neutral to alkaline pH. • NAP-MDA is photostable and solely sensitive to pH. • NAP-MDA is successfully utilized to visualize the intracellular pH. A new pH-sensitive fluorescent probe NAP-MDA was designed and synthesized. NAP-MDA consists of 1,8-naphthalimide as fluorophore, morpholine and N,N-dimethylethylenediamine as pH-responsive groups. Due to the photoinduced electron transfer (PET) mechanism, the fluorescence of 1, 8-naphthalimide was thoroughly quenched under alkaline condition (pH > 10.0), however, NAP-MDA displayed increasing fluorescence as the rise of acidity. Notably, NAP-MDA possessed an excellent linear dependence with neutral to alkaline pH (7.2–9.4), with a pKa of 8.38. NAP-MDA had good photostability and reversibility. Meanwhile, the probe was selective to pH without interference from common reactive species, temperature and viscosity. Fluorescent testing strips were fabricated with NAP-MDA and were successfully utilized to visualize the different pH with a handhold UV lamp. Confocal fluorescence imaging in live cells demonstrated that NAP-MDA mainly fluoresced in lysosomes, and could be applied for quantification of the pH within live cells. [ABSTRACT FROM AUTHOR]

We herein develop a novel two-photon fluorescent probe termed L-pH for visualization of lysosomal pH within live cells. L-pH is composed of three moieties, including naphthalimide fluorophore as a fluorescence off-on response moiety, piperazine and morpholine groups as lysosomal targeting and pH responsive sites, as well as a reactive benzyl chloride segment for further lysosomal anchoring. The experimental results demonstrate that L-pH can instantaneously respond to various pH values with high sensitivity and selectivity, and has low cytotoxicity and excellent photostability. The one-photon and two-photon fluorescence imaging data indicate L-pH can preferably accumulate into lysosome and monitor the rise of lysosomal pH changes during myriad cell stress conditions, including heat shock, cell apoptosis and mitophagy. Moreover, L-pH was applied for imaging of pH difference in abdominal tissues of mice. L-pH will be a potential tool for monitoring lysosomal pH variation during lysosome-associated physiological and pathological states. Image 1 • A new two-photon fluorescent probe termed L-pH for lysosomal pH was reported. • L-pH possesses high sensitivity and selectivity, excellent lysosome-targeted ability and low cytotoxicity. • L-pH was applied for two-photon fluorescence visualization of lysosomal pH changes during various cell stress processes. • L-pH was applied for visualization of pH difference in vivo. [ABSTRACT FROM AUTHOR]