Development of a polarity-sensitive ratiometric fluorescent probe based on the intramolecular reaction of spiro-oxazolidine and its applications for in situ visualizing the fluctuations of polarity during ER stress.

Polarity is a vital element in endoplasmic reticulum (ER) microenvironment, and its variation is closely related to many physiological and pathological activities of ER, so it is necessary to trace fluctuations of polarity in ER. However, most of fluorescent probes for detecting polarity dependent on the changes of single emission, which could be affected by many factors and cause false signals. Ratiometric fluorescent probe with "built-in calibration" can effectively avoid detection errors. Here, we have designed a ratiometric fluorescent probe HM for monitoring the ER polarity based on the intramolecular reaction of spiro-oxazolidine. It forms ring open/closed isomers driven by polarity to afford ratiometric sensing. Probe HM have manifested its ratiometric responses to polarity in spectroscopic results, which could offer much more precise information for the changes of polarity in living cells with the internal built-in correction. It also showed large emission shift ( 133 nm), high selectivity and photo-stability. In biological imaging, HM could selectively accumulate in ER with high photo-stability. Importantly, HM has ability for in situ tracing the changes of ER polarity with ratiometric behavior during the ER stress process with the stimulation of tunicamycin, dithiothreitol and hypoxia, suggesting that HM is an effective molecule tool for monitoring the variations of ER polarity.

Construction of a polymer-based fluorescent probe with dual responsive sites for monitoring changes of lysosomal viscosity.

As highly dynamic organelles, lysosomes are involved in various physiological processes. The viscosity of lysosomes plays critical roles in maintaining their normal physiological function and abnormal variations of viscosity are associated with many diseases. Monitoring the changes of lysosomal viscosity could contribute to understanding lysosome-related physiological and pathological processes. In this work, based on an indole fluorophore and fluorescent polymer, poly(2-hydroxyethyl methacrylate) (PHEM), a new polymeric fluorescent probe, In-PHEM, with dual responsive sites for tracking changes of lysosomal viscosity is presented. In-PHEM showed excellent fluorescence properties and high photostability. With this robust probe, the variation of the lysosomal viscosity in cells under different physiological conditions, including inducer stimulation, the process of starvation and apoptosis, was monitored using dual-channel imaging. Therefore, this work may provide a powerful tool for monitoring changes of lysosomal viscosity and helping to understand the relationship between the viscosity changes of lysosomes and their related diseases.

A fast fluorescent probe for tracing endoplasmic reticulum-located carboxylesterase in living cells.

Carboxylesterase (CEs), mainly localized in endoplasmic reticulum (ER), are responsible for hydrolyzing compounds containing various ester bonds. They have been closely associated with drug metabolism and cellular homeostasis. Although some CE fluorescent probes have been developed, there are still a lack of probes that could target to the ER. Here, we developed a novel fluorescent probe CR with a specific ER anchor for monitoring CEs. In CR, p-toluenesulfonamide was chosen for precise ER targeting. A simple acetyl moiety was used as the CE response site and fluorescence modulation unit. During the spectral tests, CR displayed a fast response speed (within 10 s) towards CEs. In addition, it showed high sensitivity [limit of detection (LOD) = 5.1 × 10-3 U/ml] and high selectivity with CEs. In biological imaging, probe CR could especially locate in the ER in HepG2 cells. After cells were treated with orilistat, CR succeeded in monitoring the changes in the CEs. Importantly, CR also had the ability to trace the changes in CEs in a tunicamycin-induced ER stress model. Therefore, probe CR could be a powerful molecular tool for further investigating the functions of CEs in the ER.

Monitoring cysteine level changes under LPS or H2O2 induced oxidative stress using a polymer-based ratiometric fluorescent probe.

Cysteine (Cys) is a critical amino acid that involves in many physiological and pathological processes in the human body, and it plays an important role in maintaining redox homeostasis in living systems. The concentration of intracellular Cys is abnormal under oxidative stress thus leading to many diseases. Therefore, it is significant to develop an effective method for detection of Cys under oxidative stress. In this work, we propose a new polymer-based ratiometric fluorescent probe with good selectivity and sensitivity for detecting Cys. The bioimaging experiments results show that the novel probe has a rapid ratiometric response to Cys, which can be used to monitor Cys level changes during LPS or H2O2 induced oxidative stress in living cells and zebrafish.

A fluorescent probe for specific detection of cysteine in lysosomes via dual-color mode imaging.

Biothiols, as part of the reactive sulfur species (RSS), are a class of bioactive molecules that play important physiological roles in human body. However, due to the similarity in structure and reaction sites of biothiols, it is difficult to differentiated detection them at the same time. In this work, a fluorescent probe CM-NBD combined coumarin derivative and 7-nitrobenzofurazan has been developed, which can effectively detect biothiols through simple ether cleavage. Because of a specific location group, CM-NBD can well localize in lysosomes with a high co-localization coefficient. Interesting, due to the weakly acidic environment of lysosomes, Cys can be distinguished from Hcy/GSH and H2S via dual-color mode. The probe is able not only to image exogenous biothiols but also to discriminate Cys from Hcy/GSH and H2S in cells and zebrafish model.

Single-/Dual-Responsive pH Fluorescent Probes Based on the Hybridization of Unconventional Fluorescence and Fluorophore for Imaging Lysosomal pH Changes in HeLa Cells.

As a weak acidic organelle, lysosomes maintain acidic pH ranging from 4.5 to 5.5 and abnormal lysosomal pH levels can result in functional deficiency of lysosomes. Tracking the pH changes in lysosomes will help us to understand lysosome-related biological processes and diseases. However, pH-stimuli-responsive polymer-based lysosomal pH fluorescent probe with good water solubility and biocompatibility have rarely been reported. In this work, on the basis of naphthalimide chromophore and poly(N,N-dimethylaminoethyl methacrylate), we designed lysosome-targeted fluorescent probe NapBr-PDM or NapMl-PDM with single- or dual-responsive sites for monitoring pH changes in lysosomes. Both NapBr-PDM and NapMl-PDM exhibited a narrow polydispersity index, excellent fluorescence properties, water solubility, and high photostability. The synthesized probe NapBr-PDM, with a single-responsive site, showed fast response to pH changes and well-stained lysosomes, which could monitor lysosomal pH changes in cells after incubation with chloroquine. NapMl-PDM had good lysosomes-targeting property and highly sensitive response to pH, which could track lysosomal pH changes. Moreover, NapMl-PDM achieved tracking of lysosomal pH changes in cells during lysosomal storage disorder induced by high-concentration sucrose solution for the first time. Therefore, this work provided useful tools for monitoring intracellular pH changes as well as studying the relationship between lysosomal pH and its related diseases.

Substituting copolymeric poly(alkylenetetrasulfide) for elemental sulfur to diminish the shuttling effect of modified intermediate polysulfides for high-performance lithium-sulfur batteries.

Poly(alkylenetetrasulfide) can be synthesized to replace sulfur in a chitosan-derived porous carbon (CPC) based composite cathode of lithium-sulfur batteries. Introducing a -CH2- or -CH2CH2- unit in-between the S-S bond of a polysulfide (e.g., Li2S4 → Li-S2-CH2-S-Li or Li-S-CH2CH2-S-Li) diminishes the adverse shuttling effect, proved by experimental tests and first-principle calculations.

Preparation, characterization and application of magnetic Fe3O4-CS for the adsorption of orange I from aqueous solutions.

Fe3O4 (Fe3O4-CS) coated with magnetic chitosan was prepared as an adsorbent for the removal of Orange I from aqueous solutions and characterized by FTIR, XRD, SEM, TEM and TGA measurements. The effects of pH, initial concentration and contact time on the adsorption of Orange I from aqueous solutions were investigated. The decoloration rate was higher than 94% in the initial concentration range of 50-150 mg L(-1) at pH 2.0. The maximum adsorption amount was 183.2 mg g-1 and was obtained at an initial concentration of 400 mg L(-1) at pH 2.0. The adsorption equilibrium was reached in 30 minutes, demonstrating that the obtained adsorbent has the potential for practical application. The equilibrium adsorption isotherm was analyzed by the Freundlich and Langmuir models, and the adsorption kinetics were analyzed by the pseudo-first-order and pseudo-second-order kinetic models. The higher linear correlation coefficients showed that the Langmuir model (R(2) = 0.9995) and pseudo-second-order model (R(2) = 0.9561) offered the better fits.