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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]

Acid–base balance plays a key role in regulating biological processes, and the cells must stabilize the pH within a certain range, and pH instability will cause a series of diseases. Therefore, tracking intracellular pH changes was important for understanding physiological and pathological processes. Fluorescent probes were favored by researchers as simple, fast and efficient pH detection tools, which have potential research value. In this work, a ratiometric and colorimetric sensor based on rhodamine (Rh-TPE) was fabricated for monitoring the pH change through the mechanism of fluorescence resonance energy transfer (FRET). Rh-TPE has demonstrated the advantages of high sensitivity, outstanding cell permeability and low toxicity. Moreover, the fluorescence ratio (F593/F455) of Rh-TPE displays a pH-sensitive response from 2.0 to 8.4 (pKa = 4.27) and a linear response from pH 3.3 to 5.0, which was ideal for mapping pH in living biosystems. Additionally, the results confirmed that the response signal was pH-dependent and regulated via switchable forms between closed and opened spirolactam ring forms. Spectacularly, Rh-TPE has successfully realized sensing and mapping of pH in living cells, bacteria and zebrafish. The above results exhibited that Rh-TPE could be a powerful tool for sensing and visualizing pH in living biosystems. [ABSTRACT FROM AUTHOR]

The aim of this study was to overcome the reported shortcomings of the glutathione (GSH) detection of rhodamine-based fluorescent probes, such as poor selectivity to thiol groups and reversible unstable covalent binding with the thiol groups. Here, we have developed a simple and specific fluorescent probe based on rhodamine B, which can be used to selectively detect GSH in solution and perform bioimaging in living cells. This design strategy uses a specific reaction between allenamide and the GSH thiol group, which proceeds rapidly in a phosphate buffer/tetrahydrofuran (PBS/THF) mixture with specific selectivity, and forms a stable and irreversible conjugate. The combined simplicity and specificity of the recognition process enables it to serve as a fluorescent probe for detecting GSH level changes in living cells. Such a new recognizing strategy thus may open a new window for its further application in detecting GSH levels both in vitro and in vivo. [ABSTRACT FROM AUTHOR]

Over the past decades, gallium (Ga) compounds have gained importance in the field of cancer treatment. Gallium acts as an iron mimic and disturbs iron-dependent propagation and other processes in tumor cells. However, the toxicity of gallium was also well documented in vitro and in vivo in animals. Though the oral administration of gallium in humans is less toxic, it has also been shown that a long period of administration could induce tumor fibrosis. Chromium (Cr), a naturally occurring heavy metal, is commonly used in industrial processes and can cause severe health problems in humans. It has been found to be closely involved in the metabolism of nucleic acids, proteins and fats in humans. Cr(iii) salts can be used as micronutrients and dietary supplements. However, similar to gallium (Ga3+), chromium (Cr3+) can build up to an excessive degree that is harmful to the human body. Therefore, it would be of great interest to develop chemosensing for the selective and sensitive detection of gallium and chromium ions in vitro and in vivo. Herein, we reported that an NBD-based (4-chloro-7-nitrobenzo-2-oxa-1,3-diazole) fluorescent probe (NBDT) was fabricated with demonstrated extraordinary specificity and sensitivity. A swift response toward Ga3+ and Cr3+ ions was discovered using fluorescence enhancement over a wide pH range and with cycle stability. Furthermore, lighted up by Ga3+ and Cr3+ ions in vitro, this NBDT sensor was successfully applied to detect exogenous Ga3+ and Cr3+ ions in MDA-MB-231 and HepG2 cells. Additionally, using zebrafish as the in vivo model, we demonstrated the capability of this NBDT for detecting and imaging Ga3+ and Cr3+ ions in zebrafish. Taken together, this NBDT has indicated great potential for detecting and monitoring Ga3+ and Cr3+ ions in vitro and in vivo. [ABSTRACT FROM AUTHOR]

Acid-alkaline balance plays a crucial role in all biological processes. Accordingly, monitoring pH changes will help us to understand the functional status of these physiological and pathological processes. Though fluorescent probes may be a useful tool for detecting pH changes, and there are many limitations to currently available probes, such as background interference, potential cytotoxicity, and poor cell permeability, which call for a solution urgently. In this work, a rhodamine-derived colorimetric and ratiometric sensor (Rh–HN) was fabricated for monitoring pH change via the mechanism of fluorescence resonance energy transfer (FRET). Rh–HN has been shown to possess several advantages over other probes, such as high sensitivity, outstanding permeability, and low toxicity. Besides, the fluorescence intensity ratio (F 526 /F 592) of Rh–HN displays a pH-sensitive response from 2.0 to 7.5 (p K a = 5.05) and linear response from pH 3.8 to 6.4, which was desirable for mapping pH change in the biological systems. Besides, the results indicated that Rh–HN generated a pH-dependent response regulated by switchable forms between closed and opened spirolactam ring. Overall, Rh–HN has accomplished sensing and mapping of pH in living cells, bacteria, and zebrafish. Those results demonstrated that the great potential of Rh–HN in sensing and visualizing pH in the living biosystem. Image 1 • A Rhodamine-derived sensor Rh–HN was developed to visualize and monitor pH variation with p K a = 5.05. • Rh–HN exhibited reversible colorimetric/ratiometric responses to pH by switching of closed and opened spirolactam. • Response mechanism of Rh–HN was revealed by density functional theory calculation. • Rh–HN has successfully accomplished pH mapping in living cells, bacteria and zebrafish. [ABSTRACT FROM AUTHOR]

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]

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 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]

[Display omitted] • A bodipy-based fluorescence probe for sensing O 2 − was developed. • Up to a 12.9-fold enhancement in the intensity of fluorescence was achieved. • The bodipy based probe BODIPY-T has specific selectivity for O 2 − than others. • The probe can be utilized to detect O 2 − level changes in RAW264.7 cells. The superoxide anion radical (O 2 −), a pernicious ROS in living cells, has long been recognized as an important cell signaling molecule involved in numerous physiological and pathological processes, including innate immunity and metabolic homeostasis. Here, we developed a new bodipy-based fluorescent probe for monitoring O 2 − based on the selective cleavage of phosphate bond in BODIPY-T by O 2 −, producing a high-brightness fluorescent BODIPY-COOH. The probe exhibits excellent selectivity for O 2 − with little interference from other ROS species. Fluorescence imaging of RAW264.7 cells also demonstrated successful detection of endogenous O 2 − changes in living cells, indicating that BODIPY-T is a potential probe for the diagnosis and study of the corresponding diseases. [ABSTRACT FROM AUTHOR]

Superoxide anions (O 2 •─), which are precursors of reactive oxygen species (ROS), are mainly produced in the mitochondria. This precursor of ROS is involved in both pathological and physiological processes, hence their role in many disease conditions and complications is pivotal. Though with time they are capable of being changed into related ROS species, their quantification will aid in targeting and complete eradication through numerous chemical reactions. The presence of a high reduction potential fosters the innate anionic charge to impede their reactivity with centers considered to be electron-rich. Though there are numerous quantification processes for the O 2 •─, the use of a fluorescent probe which serves as a low invasive approach with deep tissue penetration and prolonged time of analysis has emerged to change the status quo when it comes to the way of analyzing O 2 •─. Although, in some cases, this approach happens to be faced with some difficulties such as autofluorescence, photobleaching, shallow penetration, etc. This review seeks to give a general overview of the recent development in this research field, outcomes, and the yield of employing Two-photon, NIR, and other ratiometric fluorescent probes, their ability to sensitively and selectively target O 2 •─ in vivo and in vitro. Superoxide anions are involved in both pathological and physiological processes, playing a huge role in most disease conditions of an organism. Fluorescent probe possesses properties that allow the non-invasive means of quantification, imaging, and monitoring of these superoxide anions through either one-photon, two-photon fluorescence imaging, or a combination of both qualities in vivo and in vitro. [Display omitted] • Fluorescence probes present a low-invasive means for O 2.•─ detection. • Fluorescence probes sensitively and selectively target O 2.•─ in cells for bioimaging. • Detection of O 2.•─ provides a means of diagnosis of related physiological conditions. [ABSTRACT FROM AUTHOR]

[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]

[Display omitted] • ESIPT-based fluorescent probe (NBD-hnap) is prepared for sencing group IIIA ions. • NBD-hnap could be recognized group IIIA ions with fluorescence on strategy. • The response mechanism of NBD-hnap for group IIIA ions is confirmed with DFT. • NBD-hnap can visualized group IIIA ions to image in living cells and zebrafish. Aluminum (Al), gallium (Ga), indium (In) are three essential elements in group IIIA of the periodic table, which all share similar chemical properties and are also vital in many aspects of bio- and environmental systems. Proper control of their levels is thus necessary as overexposure to them has been linked to onsets of many diseases. Fluorescence based molecular probes have always been the driving horse for detecting vital ions including group IIIA ions. However, only a few such probes have been reported so far and all of them are faced with one or more shortcomings such as not very high sensitivity, incapability to detect multiple ions simultaneously, and poor cell penetration abilities due to emitted fluorescence at shorter wavelengths. To meet those challenges, we herein presented the successful development and application of a novel group IIIA ions fluorescent probe, NBD-hnap , in live RAW264.7 cell and zebrafish models, especially the imaging of ocular tumor cell OCM-1 (human choroid melanoma cells). NBD-hnap was synthesized by a simple conjugation of NBD and hnap molecules under suitable conditions. Subsequent experimental analysis and theoretical calculations confirmed that NBD-hnap forms a 1:1 chelate with each of three selected group IIIA ions. Further evaluation proved that NBD-hnap can realize highly sensitive [LODs of 113, 82 and 150 nM for Al(III), Ga(III), and In(III) respectively in aqueous solutions] and highly selective (over a dozen of interfering cations) through an ESIPT-based fluorescent sensing mechanism with strong far-red emission around 640 nm. Those value merits make NBD-hnap superior to other group IIIA ion probes reported before and NBD-hnap is thus expected to find wider and greater applications in the near future. [ABSTRACT FROM AUTHOR]

Intracellular pH was tightly regulated in many biological processes in which cells must control pH changes within a precise range. Hence, tracing intracellular pH variation was important for understanding the physiological and pathological processes. Although fluorescent probes can be a necessary tool for detecting changes in pH, there are many limitations to existing probes, such as background interference, large cytotoxicity, and poor permeability, which need to be urgently overcome. In this work, a ratiometric and colorimetric chemosensor based on spiropyran (SP-DCCH) was fabricated for monitoring pH change using fluorescence resonance energy transfer mechanism. SP-DCCH has demonstrated the advantages of high sensitivity and selectivity, outstanding permeability and hypotoxicity. Moreover, SP-DCCH displays a pH-sensitive response from 1.68 to 7.21 (p K a = 4.87) and a linear response from pH 3.81 to 6.01, which was desirable for detecting pH change in living biosystem. As expected, the results confirmed that the response signal was pH-dependent and regulated via switchable forms between spiropyran and merocyanine. Spectacularly, SP-DCCH has successfully realized sensing and mapping pH in living cells, P. aeruginosa and zebrafish. The above results exhibited that SP-DCCH could be a powerful tool for sensing and visualizing pH in living systems. Image 1 • Spiropyran-based sensor SP-DCCH has been employed for visual recognition and quantification of pH change. • SP-DCCH can be switchable sensor of pH with colorimetric/ratiometric responses via spiropyran and merocyanine. • The response mechanism of SP-DCCH was excavated by time-dependent density functional theory. • SP-DCCH has successfully realized pH mapping in living cells, bacteria and zebrafish. [ABSTRACT FROM AUTHOR]

• Novelty sensor has employed to sense ClO− with ratiometric and colorimetric. • The sensing mechanism was explored by theoretical calculation. • The chemosensors for ClO− successful response in cells, bacteria and zebrafish. • Visualized fluorescence recovery of ClO− can be realized on filter paper. Hypochlorous acid (HOCl)/hypochlorite (ClO−) was a biologically important component of reactive oxygen species (ROS) and plays a key role in human immune function systems. HOCl/ClO− can destroy invasive bacteria and pathogens, and mediate the physiological balance of the organism with low concentrations, and cause oxidation of the biomolecules such as proteins, cholesterol and nucleic acid in biological cells, leading to a series of diseases with over capacity. Therefore, quantifying the content of HOCl/ClO− in organisms are extremely urgent. In this work, coumarin-salicylic hydrazide Schiff base (CMSH), a ratiometric and colorimetric fluorescent probe for ClO- detection based on coumarin as the fluorophore unit was rationally designed and synthesized. The results indicated that CMSH exhibits high selectivity and sensitivity for ClO- identification. Additionally, the ratios (I 470 /I 532) displayed brilliant ClO−-dependent quick and sensitive performance within 40 s and limitation of 128 nM, respectively. As well as the color of the solution changes from green to colorless accompanied by the fluorescence form green turns into blue with addition of ClO−. Totally, CMSH has been successfully employed as ratiometric sensor to image in living cells, bacteria and zebrafish with low cytotoxicity and good permeability. [ABSTRACT FROM AUTHOR]

Gallium, aluminum, and indium belong to Group IIIA of the periodic table with similar chemical properties, which were a double-edged sword for living organisms. Therefore, it's particularly important to detect the content of Group IIIA in organisms. Obviously, the fluorescent probe method has become a mainstream method for detecting metal ions with advantages of convenience and high efficiency. Unfortunately, fluorescent probes that can simultaneously detect these three metal ions are rarely reported. 3-hydroxyflavone (3-HF) is a highly focused molecule with chemical and photochemical properties and have great potential for bioimaging applications as sensors with excited-state intramolecular proton transfer (ESIPT). Here, 3-HF as ratiometric fluorescence probes have been developed for responding to Group IIIA ions including Ga(III), Al(III) and In(III) ions with ESIPT-based mechanism. 3-HF displayed highly specific sensing for Group IIIA ions over other cations with a green fluorescence transformation into blue fluorescence by the formation of 2:1 complexes. However, rapid response toward Group IIIA ions was developed using ratiometric fluorescence with wide pH range and good reversibility, and the response mechanism of 3-HF toward Group IIIA ions was annotated by density functional theory (DFT). Furthermore, the biological applicability of 3-HF has shown that 3-HF were able to detect and image Group IIIA ions in cells. Additionally, using a zebrafish model, we exhibited the capability of this 3-HF probe for detecting and imaging Group IIIA ions in zebrafish. This work achieves the detection and imaging of Group IIIA simultaneously by 3-HF probe in living cells and zebrafish and provides another example for "ESIPT OFF". Image 1 • Flavone-based probe detected Group IIIA with high selectivity and sensibility. • Responding mechanism of probe towards Group IIIA was exhibited by DFT. • 3-HF as ratiometric probe sensing Group IIIA with bioimaging in cells and zebrafish. [ABSTRACT FROM AUTHOR]

The semi-metallic element gallium has repeatedly shown bio-activities in preclinical and clinical studies. Gallium derivatives have already entered clinical trials for treatment of various refractory malignancies. To better monitor or track the status of administered gallium compound, herein a novel fluorescent probe N,N',N'',N'''-Tetrakis(2-hydroxybenzylidene)biphenyl-3,3',4,4'-tetramine (bis-salophen) has been designed and synthesized. The bis-salophen probe was found to recognize gallium ions (Ga3+) with high selectivity and sensitivity over other cations via fluorescence "turn on" strategy. The spectroscopy results exhibited a 1:2 stoichiometry for probe and Ga3+, and the association constant and limit of detection were calculated as 8.85 × 106 M−1 and 13.0 nM, respectively. Additionally, base on spectroscopy and theoretical research, the mechanism of Ga3+ sensing action was explored by density functional theory (DFT), which indicated suppression of photoinduced electron transfer (PET) action along with the interruption of π-conjugation between salicylaldehyde and 3,3-diaminobenzidine backbone by Ga3+ ions. Furthermore, the biological applicability of bis-salophen probe were evaluated in various normal and cancer cell lines, results have shown that this probe is highly selective and sensitive for cancer cells. Finally, zebrafish imaging confirmed and indicated that the probe is also capable of examining Ga3+ ions. Collectively, these results suggest that we have successfully developed a novel probe for selective and sensitive detection of Ga3+ ions both in living cells and zebrafish. We expect that our work here will shed light on future development of Ga3+ detecting probes and wider application in the filed of biology and medicine shall be anticipated. Image 1 • A symmetrical bis-salophen fluorescent probe has been synthesized and recognized Ga3+ with high selectivity and sensitivity over other metal ions via fluorescence "turn on" strategy. • The chemosensing behavior of probe for Ga3+ was explored by density functional theory calculations. • The fluorescent probe for Ga3+ successful recognition in living cells and zebrafish. [ABSTRACT FROM AUTHOR]