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• A novel mitochondrion-targeting turn-on fluorescent probe RThy for detecting •OH. • Its turn on mechanism is based on the cleavage of azo-bond by •OH. • The azo group acts not only as a quenching-group but also as recognizing-group of •OH. • It successfully tracked mitochondrion •OH in live cells and zebrafish. Detection and imaging of hydroxyl radical (•OH) with high sensitivity and selectivity in biological systems is of great importance in evaluating the role of •OH plays in the physiological and pathological processes. Herein, a novel mitochondrion-targeting turn-on fluorescent probe RThy , has been developed to detect •OH in living cells and zebrafish. Probe's turn on mechanism is based on the cleavage of azo-bond by •OH. In RThy sensing system, possessing two groups: a lipophilic cation as a targeting-group, and an azo group acts not only as a quenching-group for tunable light absorption but also as recognizing-group of •OH. In the absence of •OH, almost non-fluorescence emission at 550 nm was observed. However, after reaction with •OH, bright fluorescence emission at 550 nm gradually increased with the continuous addition of •OH, displaying ˜50 folds fluorescence intensity enhancements and a quite low detection limit of 8 nM. The selectivity test showed RThy exhibits excellent selectivity toward •OH among all the ROS/RNS species tested. Furthermore, the probe has been successfully employed for imaging •OH in living cells and zebrafish, thus demonstrating RThy as a useful tool for studying •OH in practical sample application, and providing powerful theoretical basis and technical support for investigation of the interaction •OH with physiological and pathology. [ABSTRACT FROM AUTHOR]

Copper (II) is one of the most of important cofactors for numerous enzymes and has captured broad attention due to its role as a neurotransmitters for physiological and pathological functions. In this article, we present a reaction-based fluorescent sensor for Cu 2+ detection ( NIR-Cu ) with near-infrared excitation and emission, including probe design, structure characterization, optical property test and biological imaging application. NIR-Cu is equipped with a functional group, 2-picolinic ester, which hydrolyzes in the presence of Cu 2+ with high selectivity over completed cations. With the experimental conditions optimized, NIR-Cu ( 5 μM ) exhibits linear response for Cu 2+ range from 0.1 to 5 μM, with a detection limit of 29 nM. NIR-Cu also shows excellent water solubility and are highly responsive, both desirable properties for Cu 2+ detection in water samples. In addition, due to its near-infrared excitation and emission properties, NIR-Cu demonstrates outstanding fluorescent imaging in living cells and tissues. [ABSTRACT FROM AUTHOR]

We report a novel turn-on two-photon fluorescent probe ( TPNF ) for detecting formaldehyde based on aza-Cope rearrangement and intramolecular charge transfer (ICT). The probe, containing a 1,8-naphthalimide dye with a homoallylamino group, has was shown with high selectivity, sensitivity and low cytotoxicity and it was capable of detecting formaldehyde in live cells. Moreover, a time-dependent density functional theory (TD-DFT) calculation was performed to demonstrate the turn on mechanism of the probe via ICT effect. Finally, a zebrafish larvae imaging experiment reveals that TPNF displayed a significant signal change when treated with FA in vivo. These results indicated that TPNF is a promising tool in more biomedical researches. [ABSTRACT FROM AUTHOR]

• The structures of small-molecule fluorophores for plasma membrane staining were summarized. • The membrane targeting groups were categorized and summarized. • The mechanisms to achieve the membrane specificty were summarized and discussed. • The bioimaging applications of fluorescent probes were summarized. Plasma membrane (PM), a phospholipid bilayer that separates the interior of cell from the extracellular fluid, is closely involved in various cellular activities. However, monitoring dynamic membrane has always been a challenge due to its dynamic structure and complex constitution. Owing to the distinct advantages of fluorescence imaging technology, diverse small molecular fluorescent probes have been well developed for membrane staining to investigate membrane function and monitor its dynamic activity. Herein, representative small molecular fluorescent probes reported in the last ten years were summarized and categorized into four groups according to their functional membrane-anchoring moieties, namely hydrophobic alkyl chain, ammonium unit, cholesterol, and short peptide sequence. In particular, the underlying mechanisms to achieve membrane-specific fluorescence staining were fully discussed, including membrane targeting group approach, aggregation induced emission (AIE), disassembly light up fluorescence strategy and restricted intramolecular rotation (RIM). Furthermore, membrane-targeting probes for super-resolution imaging of membrane dynamics were presented as an emerging technology. In this review, we showcased recent advances in this research area, and outlined potential challenges and prospects with the goal of driving the generation of innovative fluorescent probes for PM staining. [ABSTRACT FROM AUTHOR]

Hypochlorite anion, one of the biologically important reactive oxygen species, plays an essential role in diverse normal biochemical functions and abnormal pathological processes. Herein, an efficient high-resolution mitochondria-targeting ratiometric fluorescent probe for hypochlorous acid detection has been designed, synthesized and characterized. It is easily synthesized by the condensation reaction (C C) of a 2-(2-hydroxyphenyl) quinazolin-4(3H)-one fluorophore and a cyanine group (mitochondria-targeting), which made the whole molecular a large Stokes shift (210 nm) and the two well-resolved emission peaks separated by 140 nm. As a result, it is considered as a good candidate for high resolution hypochlorous acid imaging in live cells. The ratiometric fluorescent probe exhibited outstanding features of high sensitivity, high selectivity, rapid response time (within 50 s), and excellent mitochondria-targeting ability. Moreover, the probe can also be successfully applied to imaging endogenously hypochlorous acid in the mitochondria of living cells with low cytotoxicity, and high resolution. [ABSTRACT FROM AUTHOR]

In this study, Cu(II)-mediated differential alteration of cysteine (Cys) reactivity is reported by using a Cys-specific fluorescent probe. The probe could react with Cys to give out strong fluorescence. When Cys was preincubated with Cu(II), the fluorescence of the probe was decreased due to the inhibition of Cys's reactivity by Cu(II). Remarkably, experimental results reveal that the probe could detect Cu(II) at subnanomolar concentrations. In contrast, Cu(II) could only partially inhibit the reaction between Cys and Ellman's reagent (DTNB). Furthermore, selectivity experiments show that Cu(II) is a much more potent inhibitor for Cys compared to other metal ions. Cell imaging experiments also confirm the inhibitory effects of Cu(II) on Cys's reactivity in living cells. We envision that the probe could add a useful tool for sensitive and selective detection of Cu(II) for biomedical research. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H 2 S) has recently been identified as the third gaseous signaling molecule that is involved in regulating many important cellular processes. We report herein a novel fluorescent probe for detecting H 2 S based on iminocoumarin benzothiazole scaffold. The probe displayed high sensitivity and around 80-fold increment in fluorescence signal after reacting with H 2 S under physiological condition. The fluorescent intensity of the probe was linearly related to H 2 S concentration in the range of 0–100 μM with a detection limit of 0.15 μM (3σ/slope). The probe also showed excellent selectivity towards H 2 S over other biologically relevant species, including ROS, RSS and RNS. Its selectivity for H 2 S is 32 folds higher than other reactive sulfur species. Furthermore, the probe has been applied for imaging H 2 S in living cells. Cell imaging experiments demonstrated that the probe is cell-permeable and can be used to monitor the alteration of H 2 S concentrations in living cells. We envisage that this probe can provide useful tools to further elucidate the biological roles of H 2 S. [ABSTRACT FROM AUTHOR]

Abstract: We report herein a fluorescent probe for the detection of hydrogen sulfide (H2S) with high sensitivity and selectivity. The probe is installed with double azide groups and displays high sensitivity to H2S (around 120-fold turn-on response). It reacts with H2S with high selectivity over other reactive sulfur, nitrogen, and oxygen species. The probe was also applied to detect H2S in living cells. [Copyright &y& Elsevier]

Homeostasis of iron ions takes part in a number of biological processes. Its dysregulation is associated with various diseases. However, the lack of effective fluorescent probe for detecting ferrous ion (Fe2+) severely hinders our in-depth understanding of its biological functions. Herein, the aggregation induced emission (AIE)-based probe QM-Fe for Fe2+ detection was reported. The probe demonstrated intriguing photophysical properties including near infrared emission, large Stokes shift as well as AIE characteristics. In aqueous solution, the probe also displayed rapid response, high sensitivity, and high selectivity towards Fe2+. More importantly, QM-Fe demonstrated great ability to detect endogenous and exogenous Fe2+ in living cells, showing superior property over the aggregation caused quenching (ACQ) probe DCM-Fe owing to in-situ monitoring and long-term tracking ability. We envision that this work will provide a solid basis for the development of next-generation Fe2+ fluorescent probes. • An AIE fluorescent probe QM-Fe for Fe2+ detection was reported. • The probe displays prominent properties including fast response, large Stokes shift and NIR emission. • This probe was successfully utilized to visualize exogenous and endogenous Fe2+ in HepG2 cells. • The AIE probe demonstrates priority to ACQ probe in in-situ monitoring and long-term tracking of Fe2+. [ABSTRACT FROM AUTHOR]

Lysine crotonylation plays vital roles in gene transcription and cellular metabolism. Nevertheless, methods for dissecting the molecular mechanisms of decrotonyaltion remains limited. So far, there is no single-step fluorescent method developed for enzymatic decrotonylation activity detection. The major difficulty is that the aliphatic crotonylated lysine doesn't allow π-conjugation to a fluorophore and decrotonylation can not modulate the electronic state directly. Herein, we have designed and synthesized two activity-based single-step fluorogenic probes KTcr-I and KTcr-II for detecting enzymatic decrotonylation activity. These two probes can be recognized by histone deacetylases and undergo intramolecular nucleophilic exchange reaction to generate fluorescence signal. Notably, peptide sequence-dependent effect was observed. KTcr-I can be recognized by Sirt2 more effectively, while KTcr-II with LGKcr peptide sequence preferentially reacted with HDAC3. Compared to other methods of studying enzymatic decrotonylation activity, our single-step fluorescent method has a number of advantages, such as facileness, high sensitivity, cheap facility and little material consumed. We envision that the probes developed in this study will provide useful tools to screen inhibitors which suppress the decrotonylation activity of HDACs. Such probes will be useful for further delineating the roles of decrotonylation enzyme and aid in biomarker identification and drug discovery. The first single-step fluorescent probes to detect enzymatic decrotonylation activity. Image 1 • The first single-step fluorescent probes to detect decrotonylation activity of HDACs. • The probes undergo intramolecular nucleophilic exchange reaction to generate fluorescence signal. • Peptide sequence-dependent effect for enzyme recognition was observed. • KTcr-I can be used to screen inhibitors which suppress the decrotonylation activity of enzymes. [ABSTRACT FROM AUTHOR]