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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]

[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]