Recently, the fluorescent detection of carbon monoxide (CO) in living cells has attracted great attention. However, due to the lack of effective ways to construct fluorescent CO probes, fluorescent detection of CO in living cells is still in its infancy. In this paper, we report for the first time the use of allyl ether as a reaction site for construction of fluorescent CO probes. By this way, two readily available allyl fluorescein ethers were prepared, which were found to be highly selective and sensitive probes for CO in the presence of PdCl2. These probes have the merits of good stability, good water-solubility, and rapid and distinct colorimetric and remarkable fluorescent turn-on signal changes. Moreover, a very low dose of these two probes can be used to detect and track CO in living cells, indicating that these two probes could be very promising biological tools for CO detection in living systems. Overall, this work provided not only two new promising fluorescent CO probes but also a new way to devise fluorescent CO probes.

•A new approach for development of efficient and highly selective H2S probes was reported.•Using this approach, two readily available fluorescent H2S probes were prepared.•These probes show rapid colorimetric and fluorescent turn-on response for H2S with high selectivity and sensitivity.•Fluorescent imaging of H2S in living cells was also conveniently applied.Since the biological significance of hydrogen sulfide (H2S) has been disclosed recently, great attention has been given to the development of efficient and selective fluorescent probes for H2S over other biothiols. Herein, we report that combining an aldehyde group with thiolysis of nitrobenzofurazan (NBD) ether can be used as a new approach to develop such kind of probes for H2S. Using this approach, two new fluorescent H2S probes were developed, and both of them can be used for rapid capture and visualization of H2S with excellent sensing properties including good water solubility, high selectivity and sensitivity, and distinct colorimetric and fluorescent turn-on responses. More importantly, these two probes are able to detect H2S in the presence of other biothiols. In addition, we also demonstrated that one probe can be used for fluorescent imaging of H2S in living cells with low cytotoxicity.

•A new colorimetric and ratiometric NIR fluorescent probe with enhanced fluorescence in the NIR region was reported for Cys.•This probe works well in aqueous solution around the physiological pH.•This probe shows high selectivity and sensitivity for Cys over Hcy and GSH.•This probe has low cytotoxicity and can be applied to image intracellular Cys.Ratiometric near-infrared (NIR) fluorescent probes are attractive tools for bioimaging applications. Although many fluorescent probes have been developed for detection of the biologically important cysteine (Cys), ratiometric NIR fluorescent probes for Cys are very rare, particularly those with significant fluorescence enhancement in the NIR region. In this work, a new ratiometric NIR fluorescent probe with significant NIR fluorescent turn-on changes was reported for rapid, colorimetric and ratiometric fluorescent detection of Cys. This probe is able to detect Cys in aqueous solution under mild conditions, with high selectivity and sensitivity for Cys over various analytes including the similar structured homocysteine (Hcy) and glutathione (GSH). The detection limit of this probe for Cys was found to be as low as 0.2 μM, which is far below the normal content of Cys (30–200 μM) in cells. Besides the excellent sensing properties, this probe shows low cytotoxicity and can be conveniently applied to image intracellular Cys in living cells, indicating it is a promising tool for biological applications.Download high-res image (274KB)Download full-size image

•The first colorimetric and ratiometric fluorescent CO probe was reported.•This probe shows rapid response and high selectivity and sensitivity for CO.•This probe can be used to detect CO in aqueous solution under mild conditions.•This probe can be used to develop convenient test strips for visual detection of CO gas in air.•This probe can also be used to image CO in living cells.Carbon monoxide (CO), a highly toxic gas, is now well known as an important gasotransmitter in living systems. Accordingly, development of fluorescent probes for CO is of great significance. However, fluorescent detection of CO in living systems is challenging due to the lack of effective probes, and particularly, ratiometric fluorescent probes for CO have not yet been reported. In this article, a readily available colorimetric and ratiometric fluorescent probe system for CO was reported. This probe system shows excellent sensing properties for CO including rapid response, high selectivity and sensitivity with a low detection limit (58 nM), and capable of giving distinct colorimetric and ratiometric fluorescent signal changes for CO in aqueous solution under mild conditions. In addition, this probe system has low cytotoxicity and can be used to ratiometrically detect CO in living cells. Furthermore, a very convenient paper test strip system can be developed with this probe for visual detection of CO gas. Overall, this work provided a very promising probe for colorimetric and ratiometric fluorescent detection of CO in air, aqueous solution, and living cells.Download high-res image (112KB)Download full-size image

•A novel fluorescent probe system for rapid detection of CO was reported.•This probe system is readily available and highly selective and sensitive for CO.•This probe system shows distinct colorimetric and fluorescent turn-on responses for CO.•This probe system can be used in a low dosage for fluorescent imaging of CO in living cells.Carbon monoxide (CO) is an important gasotransmitter in living systems. The biological detection of this gasotransmitter is still in its infancy and urgently needs probes. In this paper, a novel fluorescent probe system, which is based on the Pd0-mediated Tsuji–Trost reaction, is reported for rapid detection of CO both in in vitro and in living cells. This probe system is readily available and shows excellent sensing properties for CO including rapid and distinct colorimetric and fluorescent turn-on responses, high selectivity and sensitivity with a low detection limit (25 nM) in aqueous solution under mild conditions. In addition, fluorescent imaging of CO in living cells can be conveniently achieved by a low dose of this probe system.Download high-res image (101KB)Download full-size image

•A new highly selective and sensitive NIR fluorescent probe for bisulfite was reported.•This probe shows rapid response, distinct colorimetric and ratiometric fluorescent signal changes for bisulfite.•This probe can be conveniently used to detect bisulfite in real food samples.•This probe can be applied to image both exogenous and endogenous bisulfite in living cells.A novel aza-coumarin-hemicyanine conjugated hybrid was prepared, which was found to be a promising colorimetric and ratiometric near-infrared (NIR) fluorescent probe for detection of bisulfite/sulfite in aqueous solution. This probe shows a rapid response (within 30 s) and high selectivity and sensitivity for bisulfite/sulfite, giving distinct colorimetric and ratiometric fluorescence changes at 717 and 560 nm. The detection limit for bisulfite was estimated to be 87 nM. In addition, detection of bisulfite in food samples and bioimaging of both exogenous and endogenous bisulfite in living cells with this probe were successfully applied, which indicates that this probe holds great potential for bisulfite detection both in real samples and in living cells.

•A new selective fluorescent turn-on probe for detection of Cys was developed.•This probe is readily available with a simple structure.•This probe can be used to develop convenient paper test strips for Cys detection.•This probe can be applied for imaging of Cys in living cells.A new simple and readily available fluorescent probe for cysteine (Cys) was reported. This probe is based on an excited-state intramolecular proton transfer (ESIPT) dye and uses two acrylate moieties as the Cys reaction sites to promote signal changes. Importantly, this probe shows rapid fluorescent turn-on signal changes for Cys with high selectivity and sensitivity over various analytes including the similar structured homocysteine (Hcy) and glutathione (GSH) in aqueous solution under mild conditions. The detection limit of this probe for Cys was found to be as low as 0.80 μM, which is far below the normal content of Cys (30–200 μM) in cells. This probe was also successfully applied for bioimaging of intracellular Cys in living cells with low cytotoxicity. Besides, a paper test strip system was developed with this probe for a convenient detection of Cys.Download high-res image (196KB)Download full-size image

Carbon monoxide (CO) is an important gasotransmitter in living systems and its fluorescent detection is of particular interest. However, fluorescent detection of CO in living cells is still challenging due to lack of effective probes. In this paper, a readily available fluorescein-based fluorescent probe was developed for rapid detection of CO. This probe can be used to detect CO in almost wholly aqueous solution under mild conditions and shows high selectivity and sensitivity for CO with colorimetric and remarkable fluorescent turn-on signal changes. The detection limit of this probe for CO is as low as 37 nM with a linear range of 0–30 μM. More importantly, this probe (1 μM dose) can be conveniently used for fluorescent imaging CO in living cells.

The detection of hydrazine is of particular interest given its toxicity and high levels of use. In this paper, a new fluorescent probe was developed for rapid detection of hydrazine. This probe is chemically masked with a 2-fluoro-5-nitro-benzoic ester motif as a new reaction site for hydrazine. More importantly, unlike most probes for hydrazine in the literature that need to use high levels of organic solvents, this probe displays a fast colorimetric and fluorescent turn-on response for hydrazine with high selectivity and sensitivity in almost wholly water solution under mild conditions. The detection limit of this probe for hydrazine is about 0.10 μM (∼3 ppb) with a linear range of 0–20 μM. Further investigation showed that this probe could be used to develop an easy-to-prepare and easy-to-detect paper test strip for cheap and effective visual detection of hydrazine. In addition, this probe can be used to image hydrazine in living cells.

•A smart fluorescent probe for simultaneous detection and discrimination of H2S, Cys/Hcy and GSH was reported.•This probe is rather simple and can be readily prepared.•This probe shows rapid response for these four thiols with high selectivity and sensitivity.•Simultaneous detection and discrimination of Cys and GSH in living cells by this probe was successfully achieved.Development of a simple probe for simultaneous detection and discrimination of the most important four biothiols (H2S, Cys, Hcy and GSH) is important but a challenging task. In this paper, a very simple but versatile fluorescent probe was reported, which can be used for simultaneous detection and discrimination of H2S, Cys/Hcy and GSH. This probe not only can be easily prepared, but also shows rapid (within 150 s), selective and sensitive responses for these four biothiols with distinct fluorescent turn-on signal changes at 465 nm. Moreover, this probe is able to show unique absorbance enhancement at 540 nm for H2S, and additional fluorescence enhancement at 550 nm only for Cys/Hcy, thus providing a rapid, simultaneous detection and discrimination method for H2S, Cys/Hcy and GSH. Imaging and discrimination of Cys and GSH in HeLa Cells by this probe were also successfully applied.

•A readily prepared colorimetric and NIR fluorescent turn-on probe for rapid detection of sulfite was reported.•This probe uses long excitation wavelength (>600 nm) and shows relatively large Stokes shift (∼70 nm).•This probe has high selectivity and sensitivity for sulfite.•This probe can be applied to image sulfite in living cells with low cytotoxicity.A near-infrared (NIR) fluorescent turn-on probe for sulfite anions was developed. This probe uses naphthofluorescein as the NIR fluorophore and two levulinate groups as the reaction sites, and shows rapid response, high selectivity and sensitivity for sulfite anions with significant dual colorimetric and NIR fluorescence turn-on signal changes in DMSO-PBS buffer solution. The NIR fluorescence intensity at 695 nm (excited at 620 nm) increases linearly with sulfite concentration in a range of 0–300 μM and the detection limit was determined to be about 1.74 μM. The bioimaging experiments demonstrated that this probe has great potential for fluorescence imaging of sulfite in living cells.

An anthracene-bridged dinuclear zinc(II)–dipicolylamine complex was found to show high selectivity for ADP with a significant fluorescence enhancement over ATP, PPi and other common analytes in 100% aqueous solution. This complex can be used for fluorescence detection of ADP in living cells and for monitoring the activity of kinases.

In this paper, we report a highly selective and sensitive ratiometric NIR fluorescent probe that can be used for real-time detection of the biologically important hypochlorite with colorimetric and significant NIR fluorescent turn-on signal changes at NIR excitation wavelength. In addition, experiments showed that this probe can be applied to detect hypochlorite in tap water, serum samples, and living cells with low cytotoxicity.

In this paper, a new low dose fluorescent probe with excellent sensing properties for detection of biothiols (GSH, Cys and Hcy) was developed. This probe shows rapid response, high selectivity and sensitivity for biothiols with dual colorimetric and fluorescent turn-on signal changes. The detection limit of this probe for biothiols was found to be <10 nM based on the fluorescent detection. More importantly, this probe can be used to image biothiols effectively in living cells even with a low dose of 0.2 μM.

A new ratiometric fluorescent probe for the detection of highly toxic thiophenols was reported. To produce ratiometric fluorescence signal changes for thiophenols, this probe was designed to use a coumarin–naphthalimide dyad as the fluorescence resonance energy transfer (FRET) platform and dinitrophenyl ether as the recognition unit. This probe features high selectivity and sensitivity for thiophenols with a rapid detection process under mild conditions and remarkable fluorescence emission ratio changes (up to 340-fold). The application of this probe for thiophenol detection in real water samples was successfully applied.

A colorimetric and near-infrared fluorescent probe for thiophenols was developed. This new probe features remarkably large Stokes shift, and shows a rapid, highly selective and sensitive detection process for thiophenols with obvious colorimetric and near-infrared fluorescence turn-on responses. The detection limit of this probe for thiophenols was found to be 70 nM. In addition, this probe shows great potential for in vitro and in vivo detection of thiophenols, which was exampled by the successful application of this probe for quantitative detection of thiophenol in real water samples and fluorescence imaging of thiophenol in living cells and zebrafish.

•A new highly selective and sensitive NIR fluorescent probe for cysteine was reported.•This probe is readily available and uses long excitation wavelength.•This probe shows a rapid and a dual colorimetric and NIR fluorescent turn-on detection process.•This probe was successfully applied to image intracellular cysteine with low cytotoxicity.A readily available naphthofluorescein-based near-infrared (NIR) fluorescent probe was reported for rapid, colorimetric and NIR fluorescent turn-on detection of cysteine (Cys) with high selectivity and sensitivity over various analytes including the similar structured homocysteine (Hcy) and glutathione (GSH). This probe was successfully applied to bioimage intracellular Cys in living cells with low cytotoxicity.

We report herein a new approach, which combines fast nucleophilic addition of H2S to an aldehyde group and the subsequent intramolecular thiolysis of dinitrophenyl ether, and can be used to develop efficient and effective H2S probes.

We report a simple and readily available fluorescent probe for rapid, specific, and ratiometric fluorescent detection of the biologically important cysteine (Cys). This probe uses a visible-light excitable excited-state intramolecular proton transfer (ESIPT) dye (4′-dimethylamino-3-hydroxyflavone) as the fluorophore and an acrylate group as the ESIPT blocking agent as well as the recognition unit. Cleavage of the acrylate moiety can be achieved specifically and rapidly by Cys in aqueous solution under mild conditions, which leads to restore the ESIPT process and enables the probe to show a rapid, ratiometric fluorescent detection process for Cys with high selectivity over various analytes, including homocysteine (Hcy) and glutathione (GSH). The detection limit of this probe for Cys was found to be ∼0.2 μM and bioimaging of intracellular Cys by this probe was successfully applied in living cells, indicating that this probe holds great potential for biological applications.Keywords: bioimaging; cysteine; ESIPT; fluorescent probe; ratiometric; selectivity

A new colorimetric and fluorescent probe was reported, which can be used in a very low dosage (<20 nM) for rapid, highly selective and sensitive detection of biothiols.

The development of probes for rapid, selective, and sensitive detection of the highly toxic thiophenols is of great importance in both environmental and biological science. Despite the appealing advantages of near-infrared (NIR) fluorescent detection, no NIR fluorescent probes have been reported for thiophenols to date. Using the chemical properties of thiophenols that are able to cleave sulfonamide selectively and efficiently under mild conditions, we herein report a dicyanomethylene-benzopyran (DCMB)-based NIR fluorescent probe for thiophenols. This probe features remarkable large Stokes shift and shows a rapid, highly selective, and sensitive detection process for thiophenols with significant NIR fluorescent turn-on responses. The potential applications of this new NIR fluorescent probe were demonstrated by the quantitative detection of thiophenol in real water samples and by fluorescent imaging of thiophenol in living cells.

Combining metal–anion coordination and π–π stacking interactions, a zinc complex of a novel anthracene-based cyclophane was designed to recognise adenine nucleoside polyphosphates. This complex was found to show selective fluorescence enhancement for ATP, ADP, AMP and PPi in neutral aqueous solution. Among them, ADP induced the largest fluorescence change to the complex, while ATP showed the strongest binding affinity to the complex. This property was used to sense ATP in the presence of excess amounts of other phosphates such as ADP, AMP, PPi and Pi.

In this paper, a visible light excitable ESIPT probe was developed, which was found to be a very promising colorimetric and fluorescent sensor for rapid and selective detection of hydrogen sulfide in aqueous solution. The sensing mechanism and the application of this probe for hydrogen sulfide detection in biological serum and in simulated wastewater samples were investigated.

A new near-infrared (NIR) fluorescent probe, which contains a conjugated dicyanomethylene-benzopyran structure as the NIR fluorophore and an acrylate moiety as the reaction site, was found to be a promising NIR probe for biothiols (Cys, Hcy and GSH). This probe shows rapid response, high selectivity and sensitivity for biothiols (particularly for Cys and Hcy), accompanied by distinct color changes and significant NIR fluorescence turn on responses. The detection limit for Cys was found to be 81 nM. In addition, the imaging of biothiols by this probe was also successfully applied in living cells, indicating that this probe holds promise for applications in biological samples.

Introducing four –CH2OH groups to an anthracene bridged Zn–DPA complex was found to result in a new highly selective and controllable excimer-based fluorescent sensor for pyrophosphate in water.

In this paper, a new dual colorimetric and fluorescent probe for cyanide anions was developed. This probe contains an electron-donating phenanthroimidazole moiety and a strong electron-withdrawing indolium derivative. The detection of cyanide was performed via the fast nucleophilic attack of cyanide on the indolium group of the probe, resulting in a rapid sensing process for cyanide with obvious color and fluorescence (at two different emission channels, one in the visible region and one in the near infrared region) signal changes, and with high selectivity and sensitivity. The detection limit was found to be 26 nM in aqueous solution, and the application of this probe for cyanide detection in simulated wastewater samples was investigated.

A simple and readily available mononuclear zinc complex, which appends two anthracene groups, was unexpectedly found to show high selectivity for ADP with a unique increased fluorescence response in neutral aqueous solution.

A novel merocyanine-based chemodosimeter was developed to detect fluoride ions in aqueous solution. This chemodosimeter was found to be a highly selective and sensitive colorimetric and fluorescent sensor for fluoride, and moreover, it shows a fast response within a few minutes to fluoride, thus providing a new and very promising sensor for rapid detection of fluoride in aqueous solution.

Effective fluorescent sensing of oxalate in water is significant but still remains a challenge. By using indicator-displacement assays, a readily available macrocyclic copper(II) complex was found to show a sensitive off–on fluorescent sensing for oxalate with high selectivity and high binding affinity (>107 M−1) in water at neutral pH.

A novel NBD-phenoxo-bridged dinuclear Zn(II) complex is found to be an effective colorimetric sensor for pyrophosphate (PPi) in pure aqueous solution over a wide pH range. This sensor shows high binding affinity (Ka ≈ 3 × 108 M−1) and high selectivity for PPi, and can be also used to assay the activity of pyrophosphatase in real time.

Introducing hydrogen bond donors to a receptor was found to be an effective approach to improve both its selectivity and binding affinity for pyrophosphate in water. The crystal structure of Zn3–ADP complex showed the improvements come from the combination of H-bonding and metal coordination in a manner similar to many metalloenzymes.

Combining metal–anion coordination and π–π stacking interactions, a zinc complex of a novel anthracene-based cyclophane was designed to recognise adenine nucleoside polyphosphates. This complex was found to show selective fluorescence enhancement for ATP, ADP, AMP and PPi in neutral aqueous solution. Among them, ADP induced the largest fluorescence change to the complex, while ATP showed the strongest binding affinity to the complex. This property was used to sense ATP in the presence of excess amounts of other phosphates such as ADP, AMP, PPi and Pi.

A novel NBD-phenoxo-bridged dinuclear Zn(II) complex is found to be an effective colorimetric sensor for pyrophosphate (PPi) in pure aqueous solution over a wide pH range. This sensor shows high binding affinity (Ka ≈ 3 × 108 M−1) and high selectivity for PPi, and can be also used to assay the activity of pyrophosphatase in real time.

A simple and readily available mononuclear zinc complex, which appends two anthracene groups, was unexpectedly found to show high selectivity for ADP with a unique increased fluorescence response in neutral aqueous solution.

We report herein a new approach, which combines fast nucleophilic addition of H2S to an aldehyde group and the subsequent intramolecular thiolysis of dinitrophenyl ether, and can be used to develop efficient and effective H2S probes.

A colorimetric and near-infrared fluorescent probe for thiophenols was developed. This new probe features remarkably large Stokes shift, and shows a rapid, highly selective and sensitive detection process for thiophenols with obvious colorimetric and near-infrared fluorescence turn-on responses. The detection limit of this probe for thiophenols was found to be 70 nM. In addition, this probe shows great potential for in vitro and in vivo detection of thiophenols, which was exampled by the successful application of this probe for quantitative detection of thiophenol in real water samples and fluorescence imaging of thiophenol in living cells and zebrafish.

A new colorimetric and fluorescent probe was reported, which can be used in a very low dosage (<20 nM) for rapid, highly selective and sensitive detection of biothiols.

Effective fluorescent sensing of oxalate in water is significant but still remains a challenge. By using indicator-displacement assays, a readily available macrocyclic copper(II) complex was found to show a sensitive off–on fluorescent sensing for oxalate with high selectivity and high binding affinity (>107 M−1) in water at neutral pH.

In this paper, a visible light excitable ESIPT probe was developed, which was found to be a very promising colorimetric and fluorescent sensor for rapid and selective detection of hydrogen sulfide in aqueous solution. The sensing mechanism and the application of this probe for hydrogen sulfide detection in biological serum and in simulated wastewater samples were investigated.