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Although hypochlorous acid (HClO/ClO−) is regarded as a harmful reactive oxygen species (ROS) in cells, it plays an essential role in many physiological and pathological processes, such as an innate immunity and metabolic balance. In this paper, we developed a new carboxy Bodipy-based probe for rapid, sensitive, and specific monitoring of ClO−. Bp-S produces bright fluorescent Bp-COOH based on the selective recognition of ClO− to thiocarbamate groups. Bp-S exhibits high selectivity, high sensitivity, and high resistance to photobleaching in the recognition of ClO−. Fluorescence imaging of this probe in Hela cells and RAW264.7 cells also successfully detected changes in exogenous/endogenous ClO−, respectively, suggesting that Bp-S has high potential for future disease diagnosis and research. [ABSTRACT FROM AUTHOR]

Abnormal microenvironments (viscosity, polarity, pH, etc.) have been verified to be closely associated with numerous pathophysiological processes such as inflammation, neurodegenerative diseases, and cancer. As a result, deep insights into these pathophysiological microenvironments are particularly beneficial for clinical diagnosis and treatment. However, the monitoring of pathophysiological microenvironments is unattainable by the traditional clinical diagnostic techniques such as magnetic resonance imaging, computed tomography, and positron emission tomography. Recently, fluorescence imaging has shown tremendous advantages and potential in the tracing of pathophysiological microenvironment variations. In this context, a general discussion is provided on the state-of-the-art progress of fluorescent probes for visualizing pathophysiological microenvironments (viscosity, pH, and polarity), since 2016, as well as the future perspectives in this challenging field. [ABSTRACT FROM AUTHOR]

We present a ratiometric fluorescent probe for monitoring pH featuring superb photostability and chemostability. The down-regulation of the intracellular pH during autophagy in living cells induced by various stimuli, including several drugs and starvation, was quantified, which could provide instructive value to construct autophagy models to study the related pathological processes. [ABSTRACT FROM AUTHOR]

We describe a colorimetric and fluorescent probe 3a to detect cellular peroxynitrite with high selectivity and sensitivity. 3a was successfully applied in the bioimaging of exogenous and endogenous peroxynitrite in living cells. The up-regulation of peroxynitrite in cancer cells and normal cells during 5-fluorouracil treatment was finally monitored. [ABSTRACT FROM AUTHOR]

A colorimetric and fluorescent probe ER-ClO was presented in this work to detect cellular hypochlorite with high selectivity and sensitivity. With an organelle targeting unit, ER-ClO was successfully applied in the bio-imaging of exogenous and endogenous hypochlorite in the endoplasmic reticulum in a ratiometric manner. [ABSTRACT FROM AUTHOR]

Protons play crucial roles in many physiological and pathological processes, such as receptor-mediated signal transduction, ion transport, endocytosis, homeostasis, cell proliferation, and apoptosis. The urgent demand for pH imaging and measurement in biological systems has incited the development of fluorescent pH probes. Numerous fluorescent probes have been reported, but many lack the abilities needed for biological applications. Hence, the development of new pH probes with better biocompatibility, sensitivity, and site-specificity is still indispensable. This review highlights the recent trends in the development of fluorescent materials as essential tools for tracing pH variations in the biological processes of diverse living systems. [ABSTRACT FROM AUTHOR]

Developing effective methods to detect and image Cys in vivo has become an increasingly important area of research. In this work, two colorimetric and fluorescent sensors 1 and 2 were presented for detecting Cys with different reactive rates in an intramolecular cyclization reaction between acrylate and thiols. Probe 2 is the isomer of the probe 1 , which has greater steric hindrance than probe 1 . The performed reaction kinetics experiments showed that the reaction rates of 1 with thiols were far more rapid than those of 2 with thiols. From the observed crystal structures of these two compounds, we speculate that the larger steric hindrance around the acrylate group in probe 2 outweighs the electronic effect, thus slowing down the reaction between the acrylate and thiols. Probe 1 was successfully applied with negligible cell toxicity toward the imaging of biothiols in living cells and zebrafish. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescent probe (RMClO-2) for ClO− based on the conjugate of coumarin–rhodamine was presented, which could sense ClO− with fast response (within 5 s), high sensitivity and excellent selectivity. More importantly, RMClO-2 is the first mitochondria-targeted ratiometric fluorescent probe to image exogenous and endogenous ClO−. [ABSTRACT FROM AUTHOR]

A biotin–rhodamine–TPP conjugate (BiTClO) was reported as a real-time (within 10 s) fluorescent probe for the sensing of mitochondrial hypochlorite with excellent selectivity and high sensitivity (0.21 μM). Moreover, it is the first tumor-specific and mitochondria-targeted fluorescent probe applied in cell imaging. [ABSTRACT FROM AUTHOR]

Abstract: A coumarin-based multifunctional fluorescent sensor containing a di-2-picolylamine (DPA) moiety (1) was presented. Interestingly, this probe could similarly act as ON-OFF type fluorescent sensor for Co2+ and Cu2+, then in situ generated 1-Co(II) and 1-Cu(II) ensembles could further serve as OFF-ON type fluorescent sensors to achieve the discrimination of Zn2+ from Cd2+ and selective recognition of sulfide anion in aqueous solution via displacement approach, respectively. Specially, 1-Cu(II) could permeate the cell membrane and could be used in fluorescence imaging of S2− in living biological samples. These ON-OFF-ON type fluorescent sensors exhibited high selectivity and sensitivity towards the targets. [Copyright &y& Elsevier]

[Display omitted] • Reaction mechanisms of various types of sulfur-based fluorescent probes with HOCl. • The advantages and disadvantages of sulfur-based fluorescent probes for HOCl. • The applications of sulfur-based fluorescent probes for HOCl. Hypochlorous acid (HOCl) is an endogenously produced reactive oxygen species (ROS), which acts as a protector against microbes. However, its aberrant production is implicated in various oxidative-stress related pathophysiological processes, such as cardiovascular disorders, arthritis, and neurodegenerative diseases. Therefore, the direct, rapid, sensitive, and selective detection of endogenous HOCl in living systems is of essential importance for better understanding the HOCl-involved chemical biology. In the last two decades, sulfur-based fluorescent probes for HOCl have been widely designed and they usually show rapid reaction rate, high selectivity and excellent sensitivity. This review summarized the advances that have been made in the development of sulfur-based fluorescent probes for HOCl, and their reaction mechanisms were emphatically discussed. Lastly, the achievements, challenges, and perspectives in this field were outlooked. [ABSTRACT FROM AUTHOR]

A coumarin TCF-based water-soluble near-infrared fluorescent probe was presented, which could be used for the rapid, colorimetric and ratiometric detection of SO2 derivatives with a detection limit of 0.27 nM. Moreover, this probe could successfully image the analyte in living cells. [ABSTRACT FROM AUTHOR]

The endogenous hypochlorite (ClO−) is a double-edged sword for cellular functions. However, the roles of ClO− in most cellular processes remains unclear because of the limitation of detection techniques. Thus, exploiting novel fluorescent probes for ClO− with improved sensing performance is of great value. In this work, we presented the preparation of a benzothiazine-fused coumarin derivative PBC with a piperazine moiety to improve its solubility and cell membrane permeability. The sulfur atom in the probe can be oxidized into sulfoxide group by ClO−, accompanied by a 150-fold emission intensity enhancement at 520 nm with prominent selectivity and sensitivity (detection limit: 6.82 nM). The rapid response (within seconds) also endowed the probe with real-time detection ability. Additionally, PBC was successfully applied in the bioimaging of exogenous and endogenous ClO− in MCF-7 cells. Image 1 • A novel benzothiazine-fused coumarin derivative PBC was prepared. • PBC showed rapid response, excellent selectivity, and superb sensitivity toward hypochlorite. • PBC was successfully utilized to detect exogenous and endogenous hypochlorite in living cells. [ABSTRACT FROM AUTHOR]

Hydrazine plays wide roles in industrial fields but causes serious safety issues due to its high toxicity and strong activity; hence, it is important to develop reliable and convenient analytical tools for detection of hydrazine. In this work, two optical probes 1 and 2 were presented for detecting hydrazine incorporating malononitrile and 2-benzothiazoleacetonitrile, respectively. Probe 1 with dicyanovinyl was demonstrated to be more highly reactive to hydrazine, owing to the stronger electron-withdrawing ability of malononitrile. Moreover, probe 1 showed excellent selectivity toward hydrazine vapor over other amines in colorimetric and fluorescence turn-on modes. The hydrazone product between probe 1 and hydrazine was also confirmed by HRMS. In addition, probe 1 -loaded TLC plates can discriminate hydrazine vapor from other volatile amines by naked eyes. Furthermore, probe 1 was successfully utilized for detection of hydrazine in living cells. Image 1 • Two phenothiazine-based probes 1 and 2 with different vinyl substituents were presented for detecting hydrazine. • Probe 1 showed excellent selectivity toward N 2 H 4 in colorimetric and fluorescence turn-on modes. • Probe 1 was successfully applied in the detection of hydrazine vapor as well as in the imaging of intracellular N 2 H 4. [ABSTRACT FROM AUTHOR]

The spatiotemporal inspection of ROS behavior during liver fibrosis (LF) progression can facilitate its diagnosis and anti-oxidant therapy. However, none of fluorescent probes for ROS has been devoted to this issue. In this study, we proposed a HOCl-specific fluorescent probe to monitor LF process for the first time. The probe was featured with easy preparation, high selectivity, superb sensitivity (0.97 nM), rapid response (within seconds), and good membrane permeability. It can monitor delicate cellular HOCl changes from various endo-sources, and discriminate different cell types (normal or cancer) according to their inherent HOCl levels. Especially, we constructed two LF rat models by either chemical treatment (CCl 4 injection) or surgical operation (bile duct ligation), and for the first time observed that HOCl level in LF tissues increased along with its stage of development while that during acute liver injury or liver cirrhosis was unchanged or reduced. The results strongly evident the potential of HOCl as a unique biomarker for LF detection and even clinical diagnosis. [Display omitted] • A probe was reported for HOCl with an ultralow detection limit of 0.97 nM. • The probe can discriminate hepatoma cells from normal liver cells. • Two kinds of liver fibrosis models were established. • HOCl level in liver fibrosis tissues increased along with its progression. [ABSTRACT FROM AUTHOR]

[Display omitted] • A benzothiazine-fused coumarin chromophore BCLD with unique polarity sensitivity was presented. • The cell uptake pattern of BCLD was investigated. • The ability of BCLD to illuminate lipid droplets was showcased. • The variations of lipid droplets during ferroptosis, cuproptosis, and autophagy were described. Dynamics of lipid droplets (LDs) in various pathological processes provides important information about lipid metabolism during theses biological processes, while only a few reports focused on this field. In this work, a benzothiazine-fused coumarin chromophore BCLD with strong fluorescence in low-polarity environment is described. It is confirmed that cyclization-induced rigidification might be a promising approach to enhance the LDs specificity of phenothiazine-based strucutres.The probe is found to enter cells through a clathrin-mediated endocytosis, and is able to monitor LDs variations in living cells, especially during various pathological processes. It is found that obvious increase in polarity of LDs during ferroptosis and cuproptosis was visualized while a dramatic decrease in the number of LDs was recorded during autophagy, indicating different lipid metabolism manners and LD dynamics in these pathological processes. This work supports the potentials of LDs as markers for drug design targeting ferroptosis, cuproptosis, and autophagy. [ABSTRACT FROM AUTHOR]

Abstract: A coumarin-based reactive probe 1 is reported for the highly selective detection of Cu+. The benzylic ether (C–O) bond of probe 1 can be cleaved selectively by the reaction with Cu+ under a physiological reducing environment, resulting in a fluorescent change. The maximum emission peak exhibited a red shift from 410nm to 472nm, and a remarkable enhancement of emission intensity ratios (I 472/I 410) from 0.26 to 13.82 was observed. [Copyright &y& Elsevier]

Lipid droplets (LDs) are closely associated various diseases, such as liver diseases and cancers. In the last decade, a mountain of fluorescent probes has been developed for LDs, while the ones bearing near-infrared (NIR) emission, superb specificity, and high stability are still lacking. In this work, we prepare a phenothiazine-derived probe that shows a suitable hydrophobicity with ClogP as 6.25 and a strong emission at 681 nm in the low polarity solvents such as 1,4-dioxane, enabling the NIR imaging of LDs. The probe is verified to showcase high chemostability, superb pH tolerance, and excellent anti-photobleaching capacity. Using the probe, the changes in the polarity, size, and number of LDs can be monitored in living cells under different stimuli. Moreover, a variety of morphological dynamics of LDs is visualized over a period of time, including fusion, fission, transfer of lipid, LD growth, and lipolysis. Utilizing its NIR feature, in vivo tumor imaging is achieved and the therapeutic efficacy of cisplatin is primarily assessed in a triple-negative breast cancer mice model using LDs as the biomarker for the first time. These results suggest that NIR-LD is potential to act as a potent imaging agent for LDs-related diseases. [Display omitted] • A NIR fluorescent probe was prepared for imaging of lipid droplets. • The probe manifests high chemostability, superb pH tolerance, and excellent anti-photobleaching capacity. • Diverse morphological dynamics of LDs is visualized, including fusion, fission, transfer of lipid, LD growth, and lipolysis. • In vivo and ex vivo tumor imaging is established in a triple-negative breast cancer mice model. [ABSTRACT FROM AUTHOR]

[Display omitted] • A fluorescent probe AS-CN was developed for simultaneous discrimination of HOCl and viscosity. • The probe showed an emission enhancement at 710 nm to viscosity or at 593 nm to HOCl. • Dynamic upregualtions of viscosity and HOCl during the formation of foam cells were monitored. • The variations of HOCl and viscosity in AS mice were visualized. The precise detection of atherosclerosis has been a research hot point since its importance in the diagnosis of cardiovascular diseases. Here we synthesized a near-infrared fluorescent probe AS-CN with a D − π − A structure, enabling independent dual-response determination of hypochlorous acid (HOCl) and viscosity during AS progression. The performance of this probe is excellent, with large Stokes shift, low detection limit, high sensitivity, and good biocompatibility. The simultaneous variations of HOCl and viscosity during the formation of foam cells were successfully investigated for the first time. Especially, we further applied it to achieve the non-invasive in vivo detection in the atherosclerotic mouse and realized the evaluation of atherosclerosis from chemical (ROS) and physical (viscosity) dimensions, respectively. We hope that AS-CN acts as a potent tool in the detection of atherosclerosis. [ABSTRACT FROM AUTHOR]

[Display omitted] • A benzophenothiazine-based fluorescent probe BPPy for HOCl was prepared. • BPPy showed rapid response, excellent selectivity, and superb sensitivity toward HOCl. • BPPy was successfully utilized to detect HOCl generation associated with diabetic cataract. Diagnosis of diabetic cataract (DC) in the early stage is of great significance for drug intervention and surgery circumvention for DC patients. However, the lack of reliable imaging tools greatly limits the diagnosis of early DC. In this context, a fluorescent probe BBPy for hypochlorous acid (HOCl) is presented based on the oxidation of phenothiazine. The probe displays apparent emission enhancement at 562 nm toward HOCl with high selectivity, superb sensitivity (detection limit: 12.6 nM), and rapid response (within seconds). Using the probe, the HOCl generation in diabetic human lens epithelial cells was monitored, as well as the HOCl down-regulation during antioxidant treatment. Therefore, it is proposed that HOCl can be a promising biomarker for DC and fluorescence imaging technique can be regarded as a candidate tool for DC diagnosis. [ABSTRACT FROM AUTHOR]

Atherosclerosis is closely associated with cardiovascular and cerebrovascular diseases, which are the leading causes of death worldwide. The early diagnosis of atherosclerosis is helpful for prevention and treatment of related diseases. The formation of foam cells with upregulated HOCl level has been considered as a hallmark of the early atherosclerosis lesion. In this work, we reported a fluorescent probe AS-ClO for the detection of mitochondrial HOCl in foam cells for the first time. Upon reaction with HOCl, AS-ClO produced a dramatic fluorescence enhancement at 520 nm. The probe showed excellent selectivity toward HOCl with a low detection limit (12.53 nM) and a rapid response (within 5s). The mitochondria targetability of the probe was further confirmed by co-imaging test. The foam cells derived from MOVAS and RAW264.7 cells pre-treated with oxidized low-density lipoprotein exhibited 12.58-fold and 10.88-fold fluorescence enhancement with the help of the proposed probe, respectively. Moreover, a higher mitochondrial HOCl level in calcified MOVAS cells was imaged for the first time. Lastly, the over-production of HOCl in abdominal aorta sections from atherosclerotic mice was observed. The probe is anticipated to be used in the diagnosis of atherosclerosis and related diseases. [Display omitted] • A mitochondria-targeted fluorescent probe AS-ClO was prepared. • AS-ClO can sensitively detect endogenous HOCl in various types of living cells. • AS-ClO was successfully utilized to detect HOCl in foam cells, calcified cells, and abdominal aorta sections from atherosclerotic mice. [ABSTRACT FROM AUTHOR]