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[Display omitted] • The high sensitivity of the probe with a detection limit of 58 nM. • Successful detection of endogenous and exogenous CO in living cells. • Capable of detecting CO in zebrafish. • NIR probe with a high signal-to-noise ratio for imaging CO in biological samples. Carbon monoxide (CO) is a highly emitted atmospheric pollutant that can pose a serious health risk when its concentration is too high. However, endogenous CO plays an important role in maintaining human health. The development of tools capable of detecting CO in environmental samples and biological samples is therefore essential. Although CO fluorescent probes have been reported, their further applications are limited by factors such as low sensitivity and emission wavelength. Here, we have constructed a CO probe with simple structure, high sensitivity, good selectivity and near-infrared (NIR) emission characteristics. The probe uses the dicyanoisophorone derivative as fluorophore and connects allyl moiety as the reaction site. After the response, the intramolecular charge transfer (ICT) process turns on and releases strong near-infrared fluorescence at 675 nm. The linear range of fluorescence intensity of the probe for CO concentration is 1–10 μM and the detection limit is as low as 58 nM. The high sensitivity and NIR emission give the probe excellent imaging of cellular exogenous and endogenous CO. Moreover, the probe can also be used to image CO in zebrafish. There is reason to believe that the probe can be a powerful tool for detecting CO concentrations in environmental samples and for analyzing the biological role of CO in organisms. [ABSTRACT FROM AUTHOR]

Sulfur dioxide (SO 2) is a significant gas signaling molecule in organisms, and viscosity is a crucial parameter of the cellular microenvironment. They are both involved in regulating many physiological processes in the human body. However, abnormalities in SO 2 and viscosity levels are associated with various diseases, such as cardiovascular disease, lung cancer, respiratory diseases, neurological disorders, diabetes and Alzheimer's disease. Hence, it is essential to explore novel and efficient fluorescent probes for simultaneously monitoring SO 2 and viscosity in organisms. We selected quinolinium salt with good stability, high fluorescence intensity, good solubility and low cytotoxicity as the fluorophore and developed a highly sensitive ratiometric probe QQD to identify SO 2 and viscosity changes based on Förster resonance energy transfer/twisted intramolecular charge transfer (FRET/TICT) mechanism. Excitingly, compared with other probes for SO 2 detection, QQD not only identified HSO 3 −/SO 3 2− with a large Stokes shift (218 nm), low detection limit (1.87 μM), good selectivity, high energy transfer efficiency (92 %) and wide recognition range (1.87–200 μM), but also identified viscosity with a 26-fold fluorescence enhancement and good linearity. Crucially, QQD was applied to detect HSO 3 −/SO 3 2− and viscosity in actual water and food samples. In addition, QQD had low toxicity and good photostability for imaging HSO 3 −/SO 3 2− and viscosity in cells. These results confirmed the feasibility and reliability of QQD for HSO 3 −/SO 3 2− and viscosity imaging and environmental detection. We reported a unique ratiometric probe QQD for detecting HSO 3 −/SO 3 2− and viscosity based on the quinolinium skeleton. In addition to detecting HSO 3 −/SO 3 2− and viscosity change in actual water and food samples, QQD could also monitor the variations of HSO 3 −/SO 3 2− and viscosity in cells, which provided an experimental basis for further exploration of the role of SO 2 derivatives and viscosity in biological systems. [Display omitted] • A dual-function fluorescent probe was designed for detecting SO 2 and viscosity. • QQD had large Stokes shift of 218 nm and wide detection rang of 1.87–200 μM. • QQD showed high sensitivity and selectivity. • QQD achieved the dual colorimetric and ratiometric fluorescent strategy. • QQD achieved the application of foods, water samples and living cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new quinoxaline-based turn-on fluorescent probe for biothiols was developed. • Detecting biothiols with at least 69-fold fluorescence enhancement. • The probe exhibited outstanding sensitivity and selectivity towards biothiols. • A promising tool for detecting endogenous and exogenous biothiols in living cells. Maintaining biothiols homeostasis is extremely important for the health of organisms. In this work, a pair of fluorescent probes (Acr-QX8A and Acr-QX9A) was designed and synthesized to monitor biothiols. The two probes applied the same fused four ring quinoxaline as the skeleton, benzyl carbamate as the linker and acryloyl group as the recognition site, whose only difference was the amino group's position on the skeleton. By comparing the optical properties, Acr-QX9A exhibited superior performances than Acr-QX8A and chosen for further studies. Probe Acr-QX9A displayed 180-fold, 135-fold and 69-fold fluorescence intensity enhancements upon interactions with Cys, Hcy and GSH respectively, owing to the release of fluorophore QX9A and the restoration of intramolecular charge transfer (ICT) process. Acr-QX9A showed good selectivity and excellent anti-interference, which could be served as the naked-eye colorimetric probe for biothiols detection. More importantly, the probe exhibited high sensitivity towards biothiols with outstanding detection of limits (75.2 nM for Cys, 92.7 nM for Hcy and 370 nM for GSH). Encouraged by the appreciable results in solutions, probe Acr-QX9A was then successfully applied as a promising tool for monitoring both endogenous and exogenous biothiols in living cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A triphenylamine based molecular probe (TPOH) is synthesized. • TPOH exhibits an extremely low toxic to HeLa cell. • TPOH has good prospects for biological and practical applications. • TPOH has the advantages of sensitive, rapidly response and low detection limit to the detection of Zn2+. A triphenylamine-based Schiff base (TPOH) was synthesized as a good fluorescent sensor for recognizing of Zn2+. The fluorescence intensity of the probe TPOH was significantly enhanced after coordination with Zn2+ with a yellow fluorescence at the excitation wavelength of 525 nm. In MeOH-H 2 O (3:7 in v/v) solution, the probe showed excellent selectively for Zn2+ over most other competing ions, which exhibited an Intramolecular Charge Transfer (ICT) mechanism in the recognition procedure. The reaction stoichiometry of 1:1 between TPOH and Zn2+ was determined based on the Job's plot and 1H NMR spectra, respectively. The HeLa cells maintained over 95 % of viability after 24 h exposure to TPOH, which identified the extremely low toxic of TPOH and can be used for in vivo cell imaging. [ABSTRACT FROM AUTHOR]

Hypochlorous acid (HOCl) is a crucial reactive oxygen species in biological systems, and its abnormal metabolism is associated with various diseases. Therefore, it is essential to accurately detect HOCl to understand its biological function and develop related therapeutic strategies for diseases. In this work, we developed a novel fluorescence probe, BCy-S , based on the twisted intramolecular charge transfer (TICT) mechanism for rapid and sensitive detection of HOCl in an aqueous solution. The probe exhibited a significant turn-on fluorescence response to HOCl, with high selectivity, rapid kinetics (less than 40 s), large Stokes shift (about 170 nm), and low detection limit (35.2 nM), based on the specific oxidation reaction of HOCl with sulfur atoms. Additionally, the outcomes of the bioimaging experiment showed that BCy-S was capable of real-time fluorescence visualization of HOCl in living HeLa cells and zebrafish. The development of BCy-S presents a new tool for investigating the physiological function of HOCl and its pathological role in diseases. [Display omitted] • A new TICT-based HOCl fluorescent probe has been designed and developed. • The probe exhibits an excellent sensitivity, large Stokes Shift and low detection limit to HOCl. • The probe could be applied for real-time fluorescence imaging of HOCl in live HeLa cells and zebrafish. [ABSTRACT FROM AUTHOR]

[Display omitted] • A fluorescent probe was synthesized based on benzopyran-chromone for detection of ONOO−. • The probe shows short response time for ONOO− (<30 s). • The probe shows specifically selectivity and a very low detection limit of 22.4 nM for ONOO−. • The probe can accurately identify endogenous and exogenous ONOO− in HeLa cells. Peroxynitrite is widely present in organisms and closely related to many pathophysiological functions. Therefore, it is of great physiological significance to develop capable probes for detecting ONOO−. In this work, a novel fluorescent probe B-Ch was designed based on the intramolecular charge transfer (ICT) effect. By means of molecular engineering, the replacement from diethylamine group to hydroxyl group has improved the detection sensitivity of the probe. After the addition of ONOO−, the solution color and fluorescence showed noticeable changes, which were visible to the naked eye. The probe showed excellent advantages: visualization, good selectivity, low sensitivity (22.4 nM), good stability and biocompatibility, exogenous and endogenous imaging of ONOO− in HeLa cells. [ABSTRACT FROM AUTHOR]

Monoamine oxidase A (MAO-A) is involved in various diseases such as heart failure (HF), prostate cancer (PCa), psychiatric disorders, etc. The precise sensing of MAO-A is important to elucidate its function in various biological processes, as well the diagnosis and treatment of related diseases. In this research, we created a brand-new fluorescence probe ANET for the specific detection of MAO-A. Propylamine moiety of ANET was specifically recognized for MAO-A and then the product EHBT was released. A well-calculated p K a value of 8.01 ± 0.02 was achieved for EHBT by pH-dependent spectra. The fluorescence at 700 nm of EHBT was observed at pH 8.0 due to the enhanced intramolecular charge transfer (ICT). The fluorescence intensity of EHBT at 559/700 nm was in a linear relationship with MAO-A concentration in the 0.375–1.50 μg/mL range. The detection limit was 19.8 ng/mL. It is well known that the environment of mitochondria is microalkaline (pH 8.0), however, other organelles are neutral or acidic. So the fluorescence at 700 nm of ANET could be notably turned on by MAO-A in mitochondria. In addition, ANET can selectively accumulate in the mitochondria through powerful electrostatic attractions. Finally, ANET was applied for specific imaging of MAO-A in mitochondria of SH-SY5Y, PC-3, and glucose-deprived (GD) H9c2 cells. [Display omitted] • A probe was developed for Monoamine Oxidases A (MAO-A) based on ICT. • ANET can selectively accumulate in the mitochondria through strong electrostatic interactions. • Since the p K a of EHBT matches the pH in mitochondria, fluorescence of EHBT can be specifically turned on at 700 nm. • ANET was capable of differentiating MAO-A overexpressing cells from other cells. [ABSTRACT FROM AUTHOR]

Highlights • Fluorometric and colorimetric modes were realized. • AIE and ICT effects controlled the detection process. • Real-time imaging were achieved in live cells and zebrafish. Abstract Since hypochlorite (ClO−) possesses the ability that oxidizes electron-rich objects with accompanying variations in spectroscopic features, we present here an effective strategy for generating new molecular-level probe that will be compatible for application in ClO− detection. This optical sensor has been established on a donor-π-acceptor (D-π-A) electronic structure derived from a pyrene derivative appended by 2-thioxo-dihydro-pyrimidine-4,6-dione (abbreviated as Py-Pd). Specifically, it can serve as a dual-mode sensor which exhibits fluorometric and colorimetric responses to the presence of hypochlorite. The high sensitivity, selectivity, fast response time (30 s) as well as low detection limit (75 nM) have been realized. Extensive spectroscopic analyses support the oxidation cleavage of bridge C C linkage leads to the transformation of Py-Pd to pyrene-2-carbaldehyde (Py-CHO). Such real-time imaging of hypochlorite has been also achieved in live cells and zebrafish model. In this sense, this molecular-based system can be employed as an indicator for early evaluation of optical responses of reactive oxygen species. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A new N-oxide based and turn on fluorescent probe for Fe2+ was developed. • The probe possessed a high selectivity for Fe2+ among various biologically relevant species and fast rapid response. • Monitoring Fe2+ with TPM fluorescence imaging for the first time. Abstract Iron is an essential element for human body, involved in important biochemical processes in the body, especially in biological oxidation. Misregulation of iron levels in the cell is concerned with serious diseases. Here, a novel two photon and turn on NIR-fluorescent probe based ICT for detection of Fe2+ is first reported. The probe exhibited brilliant selectivity and excellent sensitivity (DL = 4.5 μM), rapid response (15 min) and "naked-eye colorimetric sensor" for monitoring of Fe2+. More importantly, the probe was successfully applied to real-time monitor Fe2+ in living cell through two-photon microscopy fluorescence imaging with excitation 680 nm. [ABSTRACT FROM AUTHOR]

[Display omitted] • A dicyanoisophorone-based ICT fluorescent probe was prepared. • A strong yellow fluorescence enhancement after treatment by Hg2+. • The probe was applied to detect Hg2+ in water/food sample. Mercury ions are notoriously difficult to biodegradable, and its abnormal bioaccumulation in the human body through the food chain can cause various diseases. Therefore, the quantitative and real-time detection of Hg2+ is very extremely important. Herein, we have brilliant designed and synthesized (E)-O-(4-(2-(3-(dicyanomethylene)-5,5-dimethylcyclohex-1-en-1-yl)vinyl)phenyl) O-phenyl carbonothioate (ICM-Hg) as a selective fluorescent probe for Hg2+ detection in real samples and intracellular staining. ICM-Hg displayed high specificity toward Hg2+ by activating the intramolecular charge transfer (ICT) process, resulting in distinguished color change from colorless to bright yellow along with noticeable switch on yellow fluorescence emission. The fluorescent intensity of ICM-Hg at 585 nm shows a well linear relationship in the range of Hg2+ concentration (0–45 μM), and the detection of limit for Hg2+ is calculated to be 231 nM. Promisingly, ICM-Hg can efficiently detect Hg2+ in real samples including tap water, tea, shrimp, and crab with quantitative recovery as well as the intracellular fluorescence imaging. [ABSTRACT FROM AUTHOR]

Herein we report a new carbazole-benzo[e]indolium dye (CEBI) as a ratiometric fluorescent and chromogenic probe for sulfite (SO 3 2− ) detection based on intramolecular charge transfer (ICT) mechanism. Upon treatment with SO 3 2− , the probe CEBI displayed a remarkable fluorescence ratiometric response (∼560-fold fluorescenc enhancement) together with a color change from red to weak red and a large shift (135 nm) in emission wavelength. The experimentally observed changes in the spectral features of the probe upon addition of SO 3 2− were systematically studied using high resolution electrospray ionization mass spectrometry (HR-ESI–MS), proton nuclear magnetic resonance ( 1 H NMR), and time-dependent density functional theory (TDDFT) calculations. We found a linear relationship between the ratio of fluorescence intensities at 465 nm and 600 nm ( F 465 /F 600 ) and SO 3 2− concentration over the range of 0–40 μM with a detection limit of 0.025 μM. Moreover, the novel probe demonstrated fluorescence imaging of SO 3 2− in living cells and zebrafish, suggesting its potential in clinical diagnostics. [ABSTRACT FROM AUTHOR]

[Display omitted] • (Z)-4-(1-cyano-2-(7-hydroxynaphthalen-2-yl)vinyl)-1-methylpyridin-1-ium iodide (Mito-NPH) used pyridine salt as the receptor and naphthalenic unit as the donor for specific recognition of SO 2 derivatives based on intramolecular charge transfer (ICT) process. • Mito-NPH exhibits ultrafast response rate (within 10 s) and high selectivity toward SO 2 derivatives. • Mito-NPH can be successfully applied for imaging of mitochondrial endogenous SO 2 derivatives in live cells. Sulfur dioxide (SO 2) is a one of reactive sulfur species (RSS) that plays significant roles in many physiological processes. While abnormal levels of SO 2 in mitochondria have been related to various diseases. Hence, developing suitable fluorescent probe for monitoring SO 2 is significant in living organisms. In this research, we designed and synthesized a mitochondrial-target probe Mito-NPH featuring the graft of a strong electron-withdrawing 4-pyridiniumylacrylonitrile unit to an electron-donating naphthalenic unit that intramolecular charge transfer (ICT) process happened. The probe Mito-NPH underwent a nucleophilic addition of HSO 3 −/SO 3 2−to give fluorescent emission signal change from red to blue and exhibited specific response toward HSO 3 −/SO 3 2−over other analytes. Moreover, Mito-NPH showed ultrafast response rate (within 10 s) for HSO 3 −. Importantly, cell imaging results demonstrated that the probe can sense endogenous SO 2 in mitochondria. [ABSTRACT FROM AUTHOR]

A supramolecular fluorescent probe based on double-cavity nor-seco -cucurbit[10]uril (ns -Q[10]) was constructed using the non-covalent host-guest interactions between ns -Q[10] and positively charged Astrazon Pink FG (APFG). The intramolecular charge transfer (ICT) effect induces the APFG@ ns -Q[10] probe to emit strong orange-red fluorescence. APFG@ ns -Q[10] exhibits desirable optical properties and low toxicity, and has been successfully applied to the imaging of HK2 and HeLa cells. When APFG@ ns -Q[10] interacts with ClO-, the C C double bond in APFG is oxidized and the molecule is cleaved, which leads to the fluorescence is quenched. The specificity and sensitivity of APFG@ ns -Q[10] to ClO- allows it to be used for the detection and tracking of ClO- in cells. APFG@ ns -Q[10] demonstrates good biocompatibility, which is an excellent foundation for its application in cell imaging. • A supramolecular fluorescent probe based on ns -Q[10])was constructed using the non-covalent host-guest interactions. • APFG@ ns -Q[10] exhibits desirable optical properties and low toxicity, and was applied to the cell imaging. • The specificity and sensitivity of APFG@ ns -Q[10] to ClO- allows it to be used for the detection of ClO- in cells. [ABSTRACT FROM AUTHOR]

Mitochondrial viscosity and ONOO− are involved in various pathological and physiological processes. Abnormal viscosity or irregular ONOO− concentration would disrupt the normal function of cells. Hence, we skillfully designed and synthesized a dual-responsive probe Mito-HC-TZ for the simultaneous detection of ONOO− and viscosity by different channels. 3-ethylbenzothiazolium was acted as fluorescent rotor to regulate the twisted intramolecular charge transfer (TICT) process; the C = C of 3-ethylbenzothiazolium linked to the xanthene core could be easily broken by ONOO−. Thus, the probe responded to viscosity and ONOO− by red and orange fluorescence channels, respectively. Mito-HC-TZ had high selectivity, low cytotoxicity and wide range of pH values. The results of cell imaging experiments showed the probe could be used to respectively monitor the viscosity and ONOO− level in HepG2 cells. [Display omitted] • A NIR probe for viscosity and ONOO− according to two channels was developed. • Mito-HC-TZ could ratiometrically respond to mitochondrial viscosity and ONOO−. • Mito-HC-TZ was applied to detect the changes of viscosity and ONOO− in cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A Golgi-targetable fluorescent probe for hypochlorous acid has been reported. • The probe displays high sensitivity and high selectivity for HOCl. • The probe can be used for detection of HOCl within the Golgi apparatus of living cells. The Golgi apparatus (GA) is a vital organelle in biological systems and excess reactive oxygen species (ROS) is produced during stress in the Golgi apparatus. Hypochlorous acid (HOCl) is a significant reactive oxygen species and has strong oxidative and antibacterial activity, but excessive secretion of hypochlorous acid can affect Golgi structure or function abnormally, it will lead to a series of diseases including Alzheimer's disease, neurodegenerative diseases, autoimmune diseases, and Parkinson's disease. In present work, a novel fluorescent probe for Golgi localization utilizing naphthalimide derivatives was constructed to detect hypochlorous acid. The fluorescent probe used a derivatived 1,8-naphthalimide as the emitting fluorescence group, phenylsulfonamide as the localization group and dimethylthiocarbamate as the sensing unit. When HOCl was absent, the intramolecular charge transfer (ICT) process of the developed probe was hindered and the probe exhibited a weak fluorescence. When HOCl was present, the ICT process occurred and the probe showed strong green fluorescence. When the HOCl concentration was altered from 5.0 × 10−7 to 1.0 × 10−5 mol·L-1, the fluorescence intensity of the probe well linearly correlated with the HOCl concentration. The detection limit of 5.7 × 10−8 mol·L-1 was obtained for HOCl. The HOCl fluorescent probe possessed a rapid reaction time, a high selectivity and a broad working pH scope. In addition, the probe possessed good biocompatibility and had been magnificently employed to image Golgi HOCl in Hela cells. These characteristics of the probe demonstrated its ability to be used for sensing endogenous and exogenous hypochlorous acids within the Golgi apparatus of living cells. [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]

It is crucial to monitor intracellular pH values and their fluctuation since the organelles of cells have different pH distribution. Herein we construct a new small molecule fluorescent probe HBT-O for monitoring the subtle pH values within the scope of neutral to acid in living cells. The probe exhibited good water solubility, a marked turquoise to olivine emission color change in response to pH, and tremendous fluorescence hypochromatic shift of ∼50 nm (1718 cm −1 ) as well as the increased fluorescence intensity when the pH value changed from neutral to acid. Thus, the probe HBT-O can distinguish the subtle changes in the range of normal pH values from neutral to acid with significant fluorescence changes. These properties can be attributed to the intramolecular charge transfer (ICT) process of the probe upon protonation in buffer solutions at varied pH values. Moreover, the probe was reversible and nearly non-toxic for living cells. Then the probe was successfully used to detect pH fluctuation in living cells by exhibiting different fluorescence colors and intensity. These findings demonstrate that the probe will find useful applications in biology and biomedical research. [ABSTRACT FROM AUTHOR]

Fluorescence imaging plays an increasingly important role in biomedicine field due to its superior sensitivity and selectivity along with dynamic, real-time, in situ monitoring the occurrence and development of biological events. Therefore, it is crucial to construct a near-infrared (NIR) fluorescent molecule with excellent optical properties. Herein a NIR robust out mitochondria-targeting dye NN has been designed, synthesized and characterized, whose fluorescence properties are easily adjusted by changing the substitution position of the nitro group at the benzene ring in this fluorescent dye. NN was a unique fluorescence-enhanced nitro dye with high fluorescence quantum yields∼0.17, a large Stokes shift∼120 nm and stable chemical structure. Encouraged by this, a novel fluorescent probe NN - Sec based on intramolecular charge transfer (ICT) was constructed by grafting NN with a selenocysteine (Sec) recognition group 2,4-dinitrobenzenesulfonyl (DNBS), and it exhibited a targeted ability with great sensitivity and selectivity. Subsequently, the probe was used for NIR imaging in living cells and mice, and deep imaging results further illustrate its potential application in biosystems. The successful design of NN and NN - Sec offer a valuable theoretical basis and technical support for investigating the occurrence and development of Sec-related diseases. • A novel NIR fluorescent dye NN bearing nitro was reported with an enhanced fluorescence quantum yields. • The recognition group 2,4-dinitrobenzenesulfonyl of Sec was grafted with dye NN to synthesize fluorescent probe NN-Sec. • ANN-Sec can detect Sec in live cells and mice by high sensitivity and selectivity, accompanied by bright NIR emission. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel indanone-based fluorescent probe for detection Cys/Hcy was developed. • The stronger acceptor makes the probe with longer emission and higher activity. • The detection mechanism should be from ICT change of the probe after with Cys/Hcy. • The probe has low cytotoxicity and been applied for imaging the biothiols in cells. Effective detection of Cys and Hcy plays an important role in the diagnosis of diseases. In this work, a novel indanone-based fluorescent probe INIAc-CN for sensitively and effectively detecting Cys and Hcy was developed. The probe exhibited weak fluorescence, but obvious fluorescent enhancement after reacted with Cys/Hcy. Moreover, the good anti-interference and low cytotoxicity of the probe made it successfully applied for monitoring Cys and Hcy of in living cells. [ABSTRACT FROM AUTHOR]

Hydrazine (N 2 H 4) is carcinogenic, extremely toxic, and induces serious environmental contamination and physiological dysfunction; however, it is widely used as an industrial material. Hence, the development of a simple and effective analytical method to detect N 2 H 4 detection in both environmental and biological sectors is warranted. In this work, an intramolecular charge transfer (ICT) -based fluorescent probe 1 , namely (Z)− 1-(4-acetoxybenzyl)− 4-(1-cyano-2-(7-(diethylamino)− 2-oxo-2 H-chromen-3-yl)vinyl)pyridin-1-ium, was designed for dual-excitation (420 and 600 nm, excitation separations >160 nm), near infrared (NIR)-emissive, and ratiometric fluorescent detection of N 2 H 4. The sensing behavior of probe 1 for N 2 H 4 detection was shown to be available over a wide pH range, and detection limits of 68 nM and 569 nM were achieved at excitation wavelengths of 420 and 600 nm, respectively. In addition, probe 1 was successfully used to image mitochondrial N 2 H 4 in living cells and zebrafish. Furthermore, the probe was also capable of determining hydrazine signals in test strips and environmental soil. [Display omitted] • A dual-ratiometric fluorescent probe 1 with near-infrared emission was designed. • Probe 1 exhibited a large excitation separation up to 180 nm. • Probe 1 gives low LODs for N 2 H 4 detection at two independent excitation wavelengths. • Probe 1 could determine hydrazine within different soil samples. • Probe 1 was capable of imaging mitochondrial N 2 H 4 in living cells and zebrafish. [ABSTRACT FROM AUTHOR]

A fluorescent probe, 1,4-diethyl-7-(3-pyridin-2-yl-acroyloyl)-1,2,3,4-tetrahydro-5-oxa-1,4-diazaanthracen-6-one (probe 1 ), with an emission in near-infrared region was developed for sensitive and selective detection of biothiols. Probe 1 is essentially non-fluorescent due to the strong intramolecular charge transfer (ICT) from the electron-donating tetrahydroquinoxaline moiety to the electron-withdrawing pyridine group. Upon the treatment with biothiols, the conjugation system was broken via Michael addition reaction between biothiols and α,β-unsaturated ketone, which inhibited the ICT process and resulted in a remarkable fluorescence enhancement with an emission maximum at 660 nm. Moreover, probe 1 was successfully applied to image intracellular thiols in living cells. [ABSTRACT FROM AUTHOR]

Herein, based on 1,8-naphtholactam, we have developed twisted and conjugated fluorophores, NPM-1 and NPM-2, which featured efficient emissions in both dispersion and aggregation states with quantum yields up to 0.76 and 0.84, respectively. From spectral and density functional theory (DFT) calculation, the luminescence mechanism of both compounds was intramolecular charge transfer (ICT) in this D-A type molecules, and the structural differences lead to differences in the intensity of ICT effects. Moreover, NPM-1 exhibited efficient and stable emissions in a variety of environments due to its rational structural design. It was a sensitive lysosome-targeting dye and retains its fluorescence intensity under continuous laser irradiation. All these features made it an unprecedented chemical tool for real-time monitoring of lysosomal status and changes, leading to a better understanding of physiological and pathological processes. • A lysosome-targeting dyes with efficient emissions in both dispersion and aggregation states. • Highly conjugated and twisted structures enabling high quantum yields. • Spectral and density functional theory calculation reveals that the luminescence mechanism is ICT. • Sensitive and stable lysosome-targeting ability are demonstrated in the cell imaging. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel benzocoumarin-based fluorescent probe BL for monitoring HOCl was designed and synthesized. • BL exhibits simple synthesis, excellent selectivity, fast response (<60 s), high sensitivity (DL, 5.64 nM). • BL was successfully applied to detect HClO spiked in tap water, 84 disinfectants and lake water, and has achieved satisfying recovery rates. • BL could readily fabricate solid-state visual sensors to be used to convenient detect HClO. • BL was nontoxic andsuccessfully used to monitor the variations of endogenous/exogenous HOCl in live RAW 264.7 macrophages. Hypochlorous acid (HOCl) is widely used in daily production and life. It is also a kind of endogenously produced reactive oxygen species (ROS) in the human immune system, plays a crucial role in many pathophysiological processes. This work designed and synthesized a novel based on benzocoumarin fluorescent probe BL for specific detection HOCl. BL has brilliant selectivity, high sensitivity (5.64 nM), fast response (60 s), moderate water-solubility. The intramolecular charge transfer (ICT) sensing mechanism of BL has been verified by fluorescence, UV, MS, and density functional theory (DFT) calculations. BL can make into a solid-state visual sensor to detect HOCl conveniently. BL was also applied to detect HClO spiked in tap water, 84 disinfectants, lake water, and satisfying recovery rates. Finally, BL was low toxic and used to track the variations of endogenous/exogenous HClO in living cells successfully. Totally, BL provides a powerful and reliable monitoring tool to reveal the biological functions of HOCl and ensure safe use. [ABSTRACT FROM AUTHOR]

Abstract: A new fluorescent probe, 3-((4-([2,2′:6′,2″-terpyridin]-4′-yl)phenyl)ethynyl)-7-methoxy-2H-chromen-2-one (ZC-F7) composed of coumarin as the fluorophore and terpyridine as the receptor is designed and synthesized. Based on the intramolecular charge transfer (ICT) effect, the probe exhibits significant variation on emission wavelengths with shifts more than 100 nm after combined with Zn2+, in accordance with the conversion of emission colors from blue to green. Good selectivity and sensitivity of this probe towards Zn2+ can be found even on the ppb level in aqueous solution. The Job's plot test suggests a 1:1 stoichiometry between ZC-F7 and Zn2+. The application of the fluorescence probe in bio-imaging is also demonstrated, proving its potential usage in fields such as environment protection, water treatment and safety inspection. [Copyright &y& Elsevier]

[Display omitted] • DNPM was fabricated successfully with fully considering its binding to the primary sites in HSA. • Molecular simulation was used to assistant the design of the fluorescent probe. • DNPM exhibited a favorable HSA sensitivity and an excellent HSA binding ability. • DNPM realized fluorescent imaging of HSA in living cells. Forming a stable complex is a prerequisite for intramolecular charge transfer (ICT) probe to recognize proteins. Herein, a human serum albumin (HSA) structure-based fluorescent probe DNPM was fabricated successfully with fully considering its binding to the primary sites in HSA. Molecular simulation was used to assist the probe design. Two ICT ligands DNPM and MPM were initially designed. Both DNPM and MPM had favorable HSA binding abilities, but only DNPM had a satisfactory HSA sensitivity. Electromagnetic coupling played a key role in DNPM fluorescence enhancement. Due to the electromagnetic environment difference in protein structure, DNPM only exhibited strong sensitivity to serum albumins. DNPM could bind to Sudlow site I and site II in HSA but could not be displaced from its binding sites by common site specific drugs (e.g. phenylbutazone and ibuprofen). Besides, DNPM exhibited great potential for illumining serum albumin in living cells. The results provided a beneficial approach for designing and synthesizing high sensitive and selective fluorescent probes for proteins. [ABSTRACT FROM AUTHOR]

An AIE fluorescent probe (TPh-PyBz- β -gal) was designed and synthesized for β -gal detection based on a novel AIE fluorophore and receptor unit D -galactose residue connected by glycosidic bond. The probe exhibited selective and sensitive turn-on fluorescent responses toward β -gal with detection limit reaching to 0.22 U/mL in aqueous environment. After studied from measured data, we proposed that a possible recognition mechanism probably resulted from the cleavage of glycosidic bond along with obviously increasing fluorescent signal at 606 nm. Meanwhile, TPh-PyBz- β -gal showed low cytotoxicity, and could be successfully used for β -gal imaging in cells. An AIE fluorescent probe (TPh-PyBz- β -gal) was designed and synthesized for β -gal detection based on a novel AIE fluorophore and receptor unit D -galactose residue connected by glycosidic bond. The probe exhibited selective and sensitive turn-on fluorescent responses toward β -gal with detection limit reaching to 0.22 U/mL in aqueous environment. After studied from measured data, we proposed that a possible recognition mechanism probably resulted from the cleavage of glycosidic bond along with obviously increasing fluorescent signal at 606 nm. Meanwhile, TPh-PyBz- β -gal showed low cytotoxicity, and could be successfully used for β -gal imaging in cells. [Display omitted] • A novel AIE fluorescent probe with ICT effect was developed for selective and sensitive detection of β -gal. • The recognition mechanism could be from the cleavage of glycosidic bond along with increasing fluorescent signal at 606 nm. • The fluorescent probe shows low cytotoxicity, and can be successfully applied for β -gal imaging in living cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel fused four-ring quinoxaline was applied as the skeleton to detect H 2 O 2. • High selectivity towards H 2 O 2 in both independent and coexistence systems. • Low detection limit, wide pH tolerance, and low toxicity. • A designed off–on process for H 2 O 2 imaging in living cells. Hydrogen peroxide (H 2 O 2), a member of small-molecule reactive oxygen species (ROS), plays vital roles in normal physiological activities and the occurrence of many diseases. In this work, two off–on fluorescent probes, QX8A-H 2 O 2 and QX9A-H 2 O 2 , were firstly designed for H 2 O 2 detection with novel fused quinoxalines as the fluorophores and boronate moiety as the reaction sites. By comparing the optical properties, QX9A-H 2 O 2 with better performance was selected for further studies. QX9A-H 2 O 2 exhibited a high sensitivity to H 2 O 2 with the detection limit as low as 46 nM, and displayed a good selectivity towards H 2 O 2 over other reactants such as ROS, biothiols and various ions. The detection was based on the intramolecular charge transfer (ICT), proceeding through a sequential oxidative hydrolysis, 1,6-rearrangement elimination and decarboxylation process to release the fluorophore QX9A. Moreover, probe QX9A-H 2 O 2 was cell permeable and was successfully employed in both exogenous and endogenous H 2 O 2 imaging in living cells. [ABSTRACT FROM AUTHOR]

Abstract: The 4-propargylamino-1,8-naphthalimide based fluorescent probe 1 has been explored as a sensor for selective detection of Au3+. 4-Amino-1,8-naphthalimides, that possess typical intramolecular charge transfer (ICT) electronic characteristics, have been widely used as versatile platforms for fluorescent probes. The newly designed probe 1 contains a propargylamine moiety at C-4 of the naphthalimide chromophore that reacts with Au3+ to generate a product that has distinctly different electronic properties from 1. Specifically, the probe undergoes a remarkable change in its absorption spectrum upon addition of Au3+ that is associated with a distinct color change from yellow to light pink. In addition, a blue shift of ca. 56nm also takes place in the emission spectra of the probe. Consequently, 1 serves as a reaction-based sensor or so called chemodosimeter for Au3+. Importantly, surfactants enhance the rate of reaction of 1 with Au3+, thus, enhancing its use as a real time sensor. Finally, the results of studies probing its application to bioimaging of Au3+ in live cells show that the probe 1 has a unique ability to sense Au3+ in cells and, in particular, in lipid droplets within cells. [Copyright &y& Elsevier]

In situ imaging of nitric oxide (NO) is of great importance to study the critical roles of NO in various physiological and pathological processes. In most currently available fluorescent probes for NO, the o-phenylenediamine (OPD) based derivatives are the most greeted and studied, in which the OPD serves as the reactive site and fluorescence quencher to modulate a turn-on process via photoinduced electron transfer (PET). In this work, a unique turn-off probe containing OPD moiety, N-1 , was designed and synthesized, which was radically different from the typical PET-based turn-on fluorescent probes. By theoretical calculation of molecular orbital, it was verified that not the widely used PET mechanism, but the intramolecular charge transfer (ICT) mechanism should be responsible for the turn-off process. Probe N-1 exhibited a remarkable performance with 7-folds fluorescence intensity decrease (at 490 nm), a low detection limit (20 nM), a fast response to NO within 12 min and a high selectivity for NO over other relevant analytes. Furthermore, probe N-1 was also applied to imaging NO in living cells. All results demonstrated that the new probe N-1 could be a practical and ideal NO indicator with good biological significance. [Display omitted] • O-phenylenediamine-hemicyanine-based probe for NO with a unique turn-off property. • Theoretical calculation verified ICT rather than PET induced the turn-off process. • High selectivity towards NO with low detection limit and short response time. • N-1 was of low toxicity and successfully applied in cell imaging for NO detection. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel Near-infrared Turn-on Fluorescent probe has been synthesized. • Fast response to Selenocysteine with a large turn-on Near-infrared fluorescence signal. • Low detection limit, high selectivity and sensitivity. • Capability for identification of Sec in living cells and mice. Selenocysteine (Sec) plays critical roles in many physiological and pathological processes of human beings, thus it is of great significance to develop accurate methods for detecting and visualizing Sec. Herein, a new anthracene derivative (YZ-M5) as a near-infrared (NIR) fluorescent probe for sensing Sec was designed. Based on the target-induced modulation of the intramolecular charge transfer (ICT) process of the probe, YZ-M5 can display a rapid strong NIR fluorescence enhancement at 660 nm for Sec within 5 min. The quantitative detection range for Sec is 0–40 μM with a low detection limit of 18.5 nM. YZ-M5 also showed high selectivity and sensitivity, as well as the capability for identification of Sec in living cells and mice. [ABSTRACT FROM AUTHOR]

• An ultra-sensitive fluorescent probe TC-gal with high affinity to β-galactosidase was developed. • The detection of β-galactosidase with low background fluorescence and high signal-to-noise ratio was realized by the response of "turn-on" fluorescence of probe TC-gal. • The visualization of endogenous β-galactosidase in ovarian cancer cells and senescent cells was achieved. • The sensing mechanism based on a competition of TICT with ICT provided a novel idea for design of fluorescent biosensor. The detection of β-galactosidase is significant for identifying the occurrence of ovarian cancer and cellular senescence. Since the complexity and diversity of biological systems, fluorescent probes for biological detection are required to own good selectivity, high selectivity and strong anti-interference ability. To meet this challenge, we designed a "turn-on" fluorescent probe TC-gal by adjusting the effect of twisted intramolecular charge transfer (TICT) between intramolecular charge transfer (ICT) of the fluorophore for ultra-sensitive detecting of β-galactosidase. The β-galactosidase can specifically trigger an enhanced (more than 800 folds) light-up fluorescence of TC-gal due to attenuated TICT effect of tetraphenylethylene part and increased ICT effect induced by electron donating effect of generated hydroxyl. Such "turn-on" fluorescence selectively triggered by β-galactosidase endows probe TC-gal with low background fluorescence and high signal-to-noise ratio. It is demonstrated that designed TC-gal exhibits high selectivity, ultra-high sensitivity (LOD = 8.4 × 10−5 U/mL) and strong affinity (Km = 18.4 μM) to β-galactosidase in buffer solution with good anti-interference ability to other biological analytes. Furthermore, biocompatible probe TC-gal is successfully applied to detect endogenous β-galactosidase in ovarian cancer cells and distinguish senescent cells. We anticipate this work can inspire the generation of superior fluorescent biosensors for biological and medical application. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H 2 O 2) is associated with many physiological and pathological processes in biological systems. Here, we report 7-diethylamino-3-formyl-coumarin (Cou-CHO) as a turn-on fluorescent probe for H 2 O 2. The proposed probe employs a tandem Payne/Dakin reaction to convert the electron-withdrawing aldehyde to the electron-donating hydroxyl group, thus hindering the formation of twisted intramolecular charge transfer (TICT) state of 7-diethylaminocoumarin, and thereby resulting in a fluorescence turn-on response. Cou-CHO features high specificity, excellent sensitivity and fast response toward H 2 O 2. In particular, Cou-CHO enables the direct visualization of basal and endogenously produced H 2 O 2 in living cells. The results demonstrate that the tandem Payne/Dakin reaction can provide a new choice to develop H 2 O 2 -selective probes. [Display omitted] • A coumarin-based fluorescent probe for hydrogen peroxide is proposed. • The present probe employs a tandem Payne/Dakin reaction to convert the aldehyde to the corresponding hydroxyl group. • The turn-on fluorescence response is due to hindering formation of twisted intramolecular charge transfer state of 7-diethylaminocoumarin. • The probe enables the direct visualization of endogenous hydrogen peroxide in living cells. [ABSTRACT FROM AUTHOR]

As one kind of most important of gaseous signal molecule, hydrogen sulfide plays a significantly role in the processes of physiology and pathology. Therefore, the research on hydrogen sulfide and its related enzymes such as cystathionine-β-synthase (CBS), 3-mercaptoacetic acid thiotransferase (3MST) and cystathionine-γ-lyase (CGL) is very meaningful. In this work, a novel fluorescent probe HCB-BT was developed, which containing a hemicyanidin conjugated with benzothiazole unit though unsaturated olefinic bond as fluorophore and a 2,4-dinitrobenzenesulfonate unit as recognition group to detecting the hydrogen sulfide. The dinitrobenzenesulfonate unit quenches the fluorescence of HCB-BT by intramolecular charge transfer (ICT) process. In the presence of hydrogen sulfide, the fluorescence emission was switched on by spliting the 2,4-dinitrobenzenesulfonyl unit. The recognition mode was verified by nuclear magnetic titration and high-resolution mass spectrometry. Furthermore, the probe HCB-BT was successfully applied to detect endogenous hydrogen sulfide in living cells and mice. This probe will help uncover more physiological and pathological mysteries related to hydrogen sulfide. [Display omitted] • The NIR probe is easy to be prepared. • The probe detect HS− with ultra-sensitivity, high selectivity accompanying with a color change from purple to blue. • The detection process is rapid and the detection mechanism is simple. • The probe can be used as a useful tool for studying the physiological and pathological phenomena related to hydrogen sulfide. [ABSTRACT FROM AUTHOR]

The first endoplasmic reticulum-targeted fluorescent probe (Na-CM-ER) was designed and synthesized for monitoring carbon monoxide (CO) in endoplasmic reticulum of the living cells. • The probe Na-CM-ER is the first endoplasmic reticulum-targeted fluorescent probe for CO. • The probe Na-CM-ER shows high selectivity and sensitivity to CO. • The probe Na-CM-ER is applied for sensing exogenous/endogenous CO in the living cells. • The probe Na-CM-ER is successfully employed to monitor CO in subcellular endoplasmic reticulum. Carbon monoxide (CO) is a significant mediator in regulating endoplasmic reticulum (ER) stress, and its level may play a potential role in the treatment of vascular diseases combined with ER stress. In-situ visualization of CO in the ER helps to elucidate its physiological and pathological mechanistic behavior. Herein, a novel CO fluorescent probe (Na-CM-ER) with ER-targeting characteristics was structured. Na-CM-ER with naphthalimide as a fluorescent group, under the trigger of CO, an ICT (Intramolecular Charge Transfer) mechanism was constructed by converting a nitro group to an amino group and showed dazzling green fluorescence. Na-CM-ER exhibited satisfactory response speed, selectivity, photo-stability and sensitivity to CO in vitro. Furthermore, biological imaging experiments demonstrated that Na-CM-ER could monitor the changes of exogenous/endogenous CO in living cells and possess an ER-targeting property. To sum up, we hope that Na-CM-ER can be as a serviceable molecular tool for imaging CO in cellular ER. [ABSTRACT FROM AUTHOR]

Due to favourable efficiency and low cost, dual-response fluorescent probes play critical roles in the development of fluorescence assay system. Herein, a novel dual-response fluorescent probe (RDCN) was designed and synthesized for the detection of two environmental contaminants: hydrazine (N 2 H 4) and cyanide (CN−). Probe RDCN exhibited discriminative sensing behaviors to N 2 H 4 and CN− with different reaction mechanisms, allowing the high selectivity and sensitivity detection for N 2 H 4 and CN−. The probe itself displayed red-emitting fluorescence as a result of strong intramolecular charge transfer (ICT) between diethylamino and dicyano. After mixing with hydrazine, a new corresponding hydrazone came into being with an intense yellow fluorescence. While, the probe could also largely switch to blue fluorescence in response to CN−. Furthermore, the probe RDCN was successfully employed to determine N 2 H 4 and CN− in water samples with the detection limits of 0.08 μM and 0.33 μM, and to visualize N 2 H 4 and CN− in live cells by means of different fluorescence channels (blue and yellow channels), revealing that probe RDCN has potential applications for discriminative detection N 2 H 4 and CN− in biological environment. Image 1 • A dual-response fluorescent probe RDCN was developed for detection of hydrazine and cyanide. • Probe RDCN displayed significantly discriminative fluorescence signal towards hydrazine (red) and cyanide (yellow) based on different reaction mechanisms. • Probe RDCN could respectively and sensitively determine hydrazine (DL = 0.08 μM) and cyanide (DL = 0.33 μM). • The probe RDCN was successfully applied for imaging hydrazine and cyanide in living cells. [ABSTRACT FROM AUTHOR]

As a typical kind of endogenous reactive nitrogen species, peroxynitrite (ONOO−) is believed heavily involved in the pathogenesis of many diseases such as inflammation, neurodegenerative conditions, and cardiovascular disorders. Precisely estimating ONOO− level in cell compartments is crucial for unraveling the biological relevance of ONOO− and enabling effective control of ONOO−-associated pathogenicity but suffers from serious difficulty owing to the daunting elusive features of ONOO−, namely nanomolar level physiological concentration and millisecond level biological half-life. A new fluorescent probe capable of detecting ONOO− with limit of detection down to 1.2 nM, response time less than 1s, and high recognition specificity over other similarly interfering species was developed in this work. For the probe constructed by conjugating an isatin moiety with an electron-withdrawing tricyanofuran (TCF) moiety, the former enabled a highly selective ONOO−-mediated oxidative decarbonylation reaction while the latter significantly improved the electrophilicity of the 3-position carbonyl group of isatin moiety and therefore accelerate the ONOO−-mediated nucleophilic attack, which eventually enabled prompt and efficient recognition reaction. For the decarbonylated product featured with a released primary aniline moiety, TCF acted as an acceptor for enabling an intramolecular charge transfer (ICT) process and the remarkable change in electronic feature upon reaction with ONOO−, which generated turn-on fluorescence with large contrast and therefore the basis for ONOO− sensing. The cell fluorescence imaging performed in this work definitely verified the capability of the probe for mapping intracellular ONOO−, despite the daunting elusive features of such physiological species. A new type of fluorescent probe enabling highly specific detection of peroxynitrite anion (ONOO−) with limit of detection down to 1.2 nM, response time less than 1s, and high recognition specificity over other similar interferents was developed and its potential for mapping exogenous and endogenous ONOO− in living cells was confirmed. Image 1 • A new type of fluorescent probe for peroxynitrite anion (ONOO−) sensing with limit of detection down to 1.2 nM was developed. • The unprecedented recognition rate for ONOO− sensing with response time less than 1 s was verified. • The ability of the probe for mapping fluctuation of intracellular endogenous ONOO− was confirmed. [ABSTRACT FROM AUTHOR]

In this work, we have developed a new carbazole-based fluorescent probe (E)-1-methyl-4-(2-(5-(9-phenyl-9 H -carbazol-3-yl) thiophen-2-yl)vinyl)pyridin-1-ium (PCTP) for ratiometric and colormetric ClO− sensing. PCTP displayed red emission due to the intramolecular charge transfer (ICT) effect of phenylcarbazol moiety, while this effect can be rapidly weakened and led to the significant fluorescence change (from red to green) in the presence of ClO−. PCTP is more highly selective and sensitive towards ClO− detection than other various biological related species. The detection limit (LOD) was calculated to be 10.8 nM. More importantly, PCTP has been successfully applied in ClO− imaging in living cells and zebrafishes. • A novel colormetric and ratiometric fluorescent probe (PCTP) was designed and synthesized for detecting ClO−. • PCTP displays a low detection limit (10.8 nM) and large Stokes shift (124 nm). • PCTP successfully performed well in sensing ClO− in living cells and zebrafishes. [ABSTRACT FROM AUTHOR]

• A simple near-infrared fluorescence probe based on dicyanoisophorone was synthesized. • This probe exhibited excellent specificity in the detection of N 2 H 4 over other amino compounds. • This probe showed excellent response performance to N 2 H 4 through distinct fluorescence enhancement. • This probe was applicable for N 2 H 4 detection in living cells and real water samples. With the widespread use of N 2 H 4 , it brings potential risks to human health. In order to determine N 2 H 4 effectively in both environment and living systems, a simple near-infrared fluorescence probe was prepared for the specific response of N 2 H 4 based on the intramolecular charge transfer (ICT) mechanism. This probe provided a "turn on" fluorescence response to N 2 H 4 with characteristics including high selectivity, rapid response (within 1 min), low cytotoxicity, and low detection limit (0.022 μM). In addition, it can be used to expediently trace N 2 H 4 in HepG2 cells and water samples. Thus, Probe 1 is a promising tool to identify the level of N 2 H 4. [ABSTRACT FROM AUTHOR]