Heat stroke is one of the most serious causes of mortality. To prevent the situation, it is fundamental to research the mechanism of heat cytotoxicity. The preliminary results revealed that heat stroke and the change of lysosome acidity had some certain correlation. To further clarify their relationship, herein, we report a highly selective and sensitive fluorescence probe (NT1) for turn-on sensing of the pH value. NT2 was synthesized as control compound. Compared to NT2, NT1 showed accurate lysosome target ability. In addition, the suitable pKa value (5.67) allows NT1 to response to the changes of lysosomal pH values. Most importantly, NT1 could be used to study the correlation between the change of lysosomal pH and heat stroke. It was shown that the lysosomal pH value increasing with temperature during heat stroke. Thus, NT1 was an excellent candidate for research of the complex biological mechanism of heat stroke.

Fluorescent probes, as noninvasive tools for visualizing the metabolism of biomolecules, hold great potential to explore their physiological and pathological processes. For cysteine (Cys), however, none of the reported fluorescent probes could image the metabolic processes in living cells. To achieve this goal, we developed a coumarin derivative based on rational design of the dual recognition sites for Cys and its metabolite, SO2. The probe displayed distinct two channels with turn-on fluorescent emission toward Cys and SO2, which were successfully applied for imaging both A549 cells and zebrafish. Further, with reversible fluorescent responses toward Cys, the probe could image the enzymatic conversion of Cys to SO2 in living A549 cells in a ratiometric manner. The present work reports the first probe to image the endogenous generated SO2 without incubation of the SO2 donors.

Herein, a novel near-infrared fluorescent probe for ratiometric detection of bisulfate was designed and developed based on a conjugation of naphthopyran-benzothiazolium system. The sensor showed excellent selectivity, high sensitivity and a rapid response toward bisulfite in aqueous solution. Upon the addition of HSO3–, the sensor displayed 37-fold (I520/I630) fluorescence intensity enhancement, accompanied by an apparent color change from violet to colorless, suggesting that the sensor can be used to detect HSO3– with “naked-eye”. Notably, the addition product can be applied to the design of regenerative chemodosimeters based on the H2O2 promoted elimination of bisulfite and recovery of probe 1. Further cell and zebrafish imaging experiment demonstrated that the sensor could image the bisulfite/H2O2 redox cycle in biological system with ratiometric manners.

•Two probes had excellent sensitivity and high selectivity for ClO−.•The recognition mechanisms were studied confirmed by density functional theory calculations.•Two probes in practical application was demonstratedTwo simple, efficient turn-on fluorescent probes for hypochlorite have been rationally designed and developed by utilizing the oxidation of hypochlorite. Notably, probe 1 and 2 displayed rapid and remarkable turn-on responses to ClO− in PBS buffer solution (pH 7.4). Further, the optical properties of two probes and their ClO−-addition products were confirmed by density functional theory calculations. And detection limits of two probes for ClO− based on the definition by IUPAC were calculated for 2.882 nM and 0.354 μM. More importantly, cell imaging experiments demonstrated that probe 1 was more suitable for detecting the ClO− in living A549 cells. And both two probes had the possibility of potentially applied in practical applications such as detecting the hypochlorite concentration of tap water and river water.In this study, two efficient turn-on fluorescent probes based on 1, 8-Naphthalimide for hypochlorite have been rationally devised and constructed. The detection limits of probe 1 and 2 for ClO− were calculated for 2.882 nM and 0.354 μM. Moreover, the optical properties of two probes and their ClO−-addition products were confirmed by density functional theory calculations. And both two probes had the possibility of potentially applied in practical applications such as detecting the hypochlorite concentration of tap water and river water.

•The compound is the first ratiometric fluorescent probe for the detection of Ho3 +.•The probe exhibits a lower detection limit (6 × 10− 8 M).•Its potential application in bioimaging was also illustrated.A ratiometric fluorescent probe for the detection of Ho3 + in DMSO-aqueous medium was designed and synthesized based on 1, 8-naphthalimide. The probe displayed response to Ho3 + with a fluorescence decrease at 512 nm and enhancement at 480 nm, accompanying with a distinct fluorescence change from bright yellow-green to cyan. Besides, the probe exhibited a lower detection limit (6 × 10− 8 M) and could be used in intracellular fluorescence imaging. To the best of the knowledge, it was the first ratiometric fluorescent probe for Ho3 + detection. This probe was expected to be a useful tool for further elucidating the roles of Ho3 + in materials, biology and environment.Based on the coordination reaction between probe and Ho3+ under mild conditions, we herein report the first ratiometric fluorescent probe which features a rapid signal response time (within 200 s), a good linearity range and a low detection limit (6 × 10− 8M). The potential application of this ratiometric fluorescent probe was demonstrated by fluorescent imaging in living cells.

•A novel ratiometric fluorescent chemodosimeter for selective detection of cyanide was obtained.•The probe showed a long emission wavelengths (>600 nm) and relatively large Stokes shifts (>100 nm).•This probe also could be used to bioimaging.A new red-emitting fluorescent materials (EP1) has been designed by taking consideration of the typical asymmetrical π-conjugation structure of the isophorone skeleton, which showed a special nucleophilicity for cyanide ion. The novel probe EP1 using an isophorone-based aldehyde as color reporting group to detect CN−, which was the first time to put forward this skeleton as new color reporting group to detect analytes in the library of chemsensor. Moreover, this new saturated red-emitting fluorescent probe with a typical donor-π-acceptor structure to detect CN− was by hampered ESIPT effect, which had a prominent fluorescence “ratiometric” changes accompanied with a large stokes shifts around 150 nm. In addition, the ability of this unique probe to detect cyanide anion in living cells (A549 cells) had also been proved. These results indicated that EP1 was a highly sensitive “ratiometric” dye with promising biological applications.Download high-res image (220KB)Download full-size image

The sulfide anion is significant in industrial processes, biology and environmental science. Hence, robust fluorescent sensors for sulfide which are water soluble and biocompatible are highly desirable. Here, we developed a novel red-emitting fluorescent probe (SP1) for the sulfide anion based on cleaving the dinitrobenzenesulfonate ester to restore the fluorescence, accompanied by a long wavelength emission at 644 nm. The detection process took place in 100% PBS buffer, which suggested it had excellent water solubility. Most importantly, the ability of SP1 to detect sulfide anions in living cells (MCF-7 cells) and zebrafish has also been proven.

•Two red-emission fluorescent probes were synthesized by a ‘one-pot’ reaction.•We concentrated on the comparative investigation on two probes abilities for H2S.•The long-emission probe can be used to imaging endogenous H2S using S-Nitroso-N-acetyl-DL- penicillamine (SNP) stimulating in cells and zebrafish.The gasotransmitter hydrogen sulfide (H2S) has attracted attention in recent years for its contributions to human health and diseases. In this work, the design strategy relied on ‘one-pot’ by employing BODIPY 1 dye and P-hydroxybenzaldehyde afforded two key intermediates, then further reacted with NBD thus obtaining products ‘single’ and ‘double’ arms types molecules (BDP-N1 and BDP-N2). Firstly we concentrated on the comparative investigation their response abilities for hydrogen sulfide. The response mechanisms are all based on the selective thiolysis of 7-nitrobenzo[c-1,2,5] oxadiazole(NBD) moiety attached to the styryl-BODIPY scaffold by H2S. However, it is worth mentioned that double‘arms’showed longer wavelength excitation and emission resulting from extended conjugation. Furthermore, these successes of intracellular imaging experiments in A549 cells indicated that the two probes are suitable for imaging of exogenous or endogenous hydrogen sulfide in living cells or living zebrafish.

AbstractThiole wie Cystein (Cys), Homocystein (Hcy) und Glutathion (GSH) spielen für das Redoxgleichgewicht in biologischen Systemen eine entscheidende Rolle. Dieser Kurzaufsatz fasst aktuelle Aspekte aus dem Bereich der reaktiven Thiolsonden für die biomedizinische Forschung und Diagnostik zusammen und betont die verbleibenden Herausforderungen für Chemiker im Bereich der selektiven Sonden und Sensoren. Der Fortschritt bei Sonden mit mehreren Bindungsstellen stellt eine kreative neue Richtung des Feldes dar, die gleichzeitige und akkurate ratiometrische Messungen ermöglichen kann. Neue Strategien zur Entwicklung von Sonden können helfen, aktuelle Aufgaben anzugehen. Dazu zählt das Monitoring von Krankheiten, die durch abweichende GSH-, Cys- und Hcy-Spiegel gekennzeichnet sind, wie etwa Autismus und chronische Erkrankungen, die auf oxidativem Stress beruhen.

•A novel NIR fluorescent material was prepared firstly and characterized fully.•The material can specially recognize HS−/CN− as a colorimetric and fluorescent probe.•The NIR fluorescent material was successfully used to detect endogenous H2S in A549 cells under SNP induced.A novel NIR fluorescent material, which is constructed with interweaved quinline and benzimidazole as the fluorophore system, indolium as a dye and reactive site under connected double bond conjugation. The sensor mechanism relied on strong nucleophilic attack of only HS−/CN− which shortened the conjugated system resulting in the fluorescent spectral changes as well as a change in color. Other nucleophilic reagents such as thiols and bisulfate did not undergo the reaction and therefore did not induce color and fluorescence changes. The pretty 1H NMR titration results strongly proved the nucleophilic mechanism. The fluorescent material was successfully used to detect endogenous H2S in A549 cells using S-Nitroso-N-acetyl-DL- penicillamine (SNP), a commercial NO donor to stimulate production of H2S and exogenous H2S.A novel NIR fluorescent material was constructed. Only strong nucleophiles such as HS−/CN− could attack and shorten the conjugated system resulting in the color and fluorescence change, thiols and bisulfate did not undergo the reaction. The material was showed a success application by A549 cell imaging under SNP stimulation.Download high-res image (73KB)Download full-size image

•A new “off-on” sensor which can fluorescence discriminate GSH from Cys/Hcy at intracellular concentrations.•The significantly different mechanisms enable the discrimination of GSH over Cys/Hcy through fluorescence response.•The probe has a good cell membrane permeability that can be applied in bioimaging in living cells.Glutathione (GSH) is the most abundant intracellular thiol with the concentration in the millimolar range. It has also been reported that GSH plays a crucial role in human pathologies, so it is meaningful to develop an effective probe for GSH. In this work, we report a coumarin-chlorine malononitrile “off-on” sensor for highly selective fluorescence detection of GSH over Cys/Hcy. The chlorine of the probe can be rapidly replaced by thiolates of biothiols through thiol-halogen nucleophilic substitution. The amino groups of Cys/Hcy but not GSH further replace the thiolate to form amino-substituted compound. Subsequently, an intramolecular Michael addition between the α,β-unsaturated malonitrile and thiol group may occur. However, GSH only forms thiol-substituted compound. The significantly different mechanisms enable the discrimination of GSH over Cys/Hcy through fluorescence response. Finally, fluorescence imaging of A549 cells indicated that probe 1 could be used for monitoring GSH in living cells. It would be a useful tool to understand the mechanisms of many related diseases.The statement: A coumarin-based “off-on” sensor was designed and synthesized, which was able to fluorescence selectivily discriminate GSH from Cys/Hcy. The significantly different mechanisms enable the discrimination of GSH over Cys/Hcy through fluorescence response. Finally, fluorescence imaging of A549 cells indicated that 1 could be used for monitoring GSH in living cells.Download high-res image (85KB)Download full-size image

•A ratiometric fluorescent probe for detection of H2S was prepared.•The fluorescent probe displayed excellent water solubility.•The fluorescent probe with biocompatibility can detect endogenous H2S in living cells.The third gasotransmitter hydrogen sulfide (H2S) plays a vital role to human health and diseases. A water-soluble ratiometric fluorescent probe (HS-1) for hydrogen sulfide (H2S) has been developed, which resulted in an increase of the emission at 403 nm along with a concomitant decrease of fluorescence peak at 519 nm, the ratios of emission intensities at 403 and 519 nm (I403/I519) displayed an increase from 0.27 to 8.54. This probe showed excellent selectivity toward H2S over other common anions and biothiols. Furthermore, these successes of intracellular imaging experiments in A549 cells indicated that this probe is suitable for imaging of ex-/endogenous hydrogen sulfide in living cells.A novel fluorescence H2S probe based on tandem nucleophilic substitution/cyclization reaction was obtained, which is a ratiometric fluorescent probe possessing good water solubility, membrane permeability, and compatibility with living cells for selective detection of ex-/endogenous H2S in living cells.Download high-res image (263KB)Download full-size image

•The probe is a novel fluorescent probe for the detection of Mg2+ with a 2: 1 coordination between probe and Mg2+.•The probe showed a low detection limit 5.01 × 10−8 M and 45 s response time for Mg2+ detection.•The probe is nearly non-toxic and could be applied in bioimaging.A novel “off-on” fluorescent probe based on 1, 8-naphthalimide derivative for the detection of Mg2+ in ethanol solution was designed and synthesized. The probe displayed responses to Mg2+ with a fluorescence enhancement at 523 nm, accompanying with a distinct fluorescence change from nearly colorless to bright yellow-green. Besides, the probe showed a rapid detection process (45 s), high fluorescence enhancement (up to 15-fold), a good binding constant (6.17 × 105 M−1) and a low detection limit of Mg2+ (5.01 × 10−8 M). Moreover, density functional theory (DFT) calculations were also performed to support the responding mechanism between the probe and the coordination complex. In addition, the cell cytotoxicity experiments suggested that the probe is nearly non-toxic and the fluorescence scanning microscopic experiments demonstrated that the probe was capable of monitoring at the intracellular Mg2+ level successfully.Download high-res image (157KB)Download full-size image

Intracellular pH values are some of the most important factors that govern biological processes and the acid–base homeostasis in cells, body fluids and organs sustains the normal operations of the body. Subcellular organelles including the acidic lysosomes and the alkalescent mitochondria undergo various processes such as intracellular digestion, ATP production and apoptosis. Due to their precise imaging capabilities, fluorescent probes have attracted great attention for the illustration of pH modulated processes. Furthermore, based on the unique acidic extracellular environment of acidic lysosomes, fluorescent probes can specifically be activated in cancer cells or tumors. In this review, recently reported lysosome and mitochondria specific pH imaging probes as well as pH-activatable cancer cell-targetable probes have been discussed.

•The interaction between probes and CN in solution was studied in detailed.•Probe 1 can be applied in bioimaging.•The detection limit is as low as 10−8M.In this work two novel fluorescent imaging materials for CN with twin binding groups (1 and 2) have been synthesized and fully characterized by standard analytical tools and spectroscopic techniques. The selectivity of 1 and 2 has been explored in aqueous solution, and the resulting turn-on fluorescence response toward CN among different anions was studied. The cyanide ion adduct was characterized using NMR and mass spectroscopy and detection mechanism was further confirmed to be the nucleophilic attack of the indolium group of probe by CN, which induces a turn-on fluorescence change. NMR and mass spectra indicate nucleophilic addition of CN to indolium group is reversible in ionization process. For the practical application of the sensors, 1 could be used for fluorescence-microscopic imaging of CN in biological applications.Based on the nucleophilic attack of the indolium group by CN under mild conditions, we herein report two new fluorescent probe which features a rapid signal response time, a good linearity range and a low detection limit. The potential application of this new fluorescent probe was demonstrated by fluorescent imaging of CN in living cells.

•The fluorescent sensor was the first alkyne fluorescent probe with excellent water-solubility for the detection of Pd2+.•The mechanism via catalytic-depropargylation to form oxime.•This probe also could be used to bioimaging.Palladium is significant in chemistry, biology and environmental science, while as a toxic metal, it could have adverse effects on our health and the environment. It is thus critical to monitor the changes of Pd (II) in living cells. Here, we developed a new colorimetric and fluorometric probe (TP1) based on palladium(II)-involved reactivity. Compared with the reported Pd (II) sensors, TP1 was the first alkyne compound fluorescent probe with excellent water-solubility for Pd2+, which was via catalytic-depropargylation to form oxime for the detection of Pd2+ within a rapid response time 80 s. The detection limit of TP1 toward Pd(II) was estimated as 0.47 μM. In addition, the ability of the TP1 to detect Pd(II) in living cells (HepG2 cells) has been also proven. These results indicated that TP1 was a highly sensitive turn-off Pd(II) dye with promising biological applications.A new fluorescent prob e for Pd2+ based on triphenylamine was developed. Among the tested metal ions, only Pd2+ could turn off the fluorescence intensity suggesting that the probe was a highly selective sensor for Pd2+. More importantly, the probe featured a rapid signal response time (within 80 s). In addition, the ability of the probe to detect Pd(II) in living cells (HepG2 cells) via quenching of the fluorescence had also been proved.

The reaction of salicylhydroxamic acid with hypochlorite produces 1,2-benzisoxazoline-3-one, a heterocycle that contains a fluorophore. As a result, this reaction was used as the basis for a new, selective and sensitive fluorescence system for the recognition of hypochlorite. The effectiveness of the method was demonstrated by its use to detect hypochlorite in a disinfectant solution as well as to image hypochlorite in cells.

We report herein a highly selective and sensitive turn-on fluorescent probe (compound 1) with a fast response time (less than 2 min) for thiophenol detection based on an “enhanced SNAr” reaction between thiophenols and a sulfonyl-ester moiety covalently attach to curcumin. Reaction of 1 in Hepes–MeOH (1:1, v/v, pH 7.4) in the presence of 4-methylthiophenol (MTP) resulted in a remarkable enhancement of the fluorescence. A linear response in the presence of MTP of the relative fluorescent intensity (F – F0) of 1 at 536 nm in the 0–40 μM MTP concentration range was found. A limit of detection (LOD) for the detection of MTP of 26 nM, based on the definition by IUPAC (CDL = 3 Sb/m), was calculated. Probe 1 was applied to monitor and imaging exogenous MTP in live cells and to the detection of MTP in real water samples.

•All kinds of fluorophores in Zn2+ fluorescent probes were classified.•Sensing applications results from their complexing and basic properties were discussed.•This review brings forward the current status in the design and development of Zn2+ fluorescent probes.With the biological importance of zinc, the development of probes for zinc has been an active research area in recent years. With the aim of designing, synthesising and applying fluorescent sensors for Zn2+, this review provides an insight into Zn2+ sensors based on different fluorophores over past decades and their applications in the detection of zinc. Several types of fluorophores have been reported, including quinoline, rhodamine, coumarin, fluorescein, 4-amino-1,8-naphthalimide, Dipyrrometheneboron Difluoride, pyrene, porphyrin and others. It is of greatest importance that selects the suitable fluorophores for the design and synthesis of outstanding selective colorimetric or fluorimetric probes for detection of Zn2+ in living cell. Based on the versatile means of modification in these fluorophores, we can envision that there still present ample opportunities for designing efficient and novel fluorescent probes for the detection of Zn2+ in biological and environmental.The detection of zinc has long held the attention of the research area because of the biological importance. This review highlights the advances in the development of fluorescent and/or colorimetric probes, and the probes are classified according to fluorophores into seven categories including (1) quinoline, (2) rhodamine, (3) coumarin, (4) fluorescein, (5) 4-amino-1,8-naphthalimide, (6) BODIPY, (7) pyrene, (8) porphyrin. We hope that this review will help to design highly selective simple fluorescent and/or colorimetric probes for Zn2+ detection of in living cell.

•The interaction between probe 1 and thiophenol in solution was studied in detailed.•The probe can be applied in bioimaging.•The detection limit is as low as 13 nM.Thiophenols, a class of toxic and polluting compounds, are widely used in industrial production. Meanwhile, some aliphatic thiols play important roles in living organisms. Therefore, the development of probes for specific thiophenol detection is of great importance. Herein, a novel highly sensitive and selective ‘off-on’ fluorescent probe for detecting thiophenols has been developed by an ICT mechanism through a rational design. The probe displays a large Stokes shift (140 nm) and 60-fold fluorescence intensity enhancement. More importantly, the probe features a rapid signal response time (within 100 s), a good linearity range and the detection limit is as low as 13 nM. In addition, the ability of the probe to detect thiophenols in living cells (HepG2 cells) via an enhancement of the fluorescence has also been demonstrated.A novel highly sensitive and selective ‘off-on’ fluorescent probe for detecting thiophenols has been developed by an ICT mechanism through a rational design. It displays a large Stokes shift (140 nm), a good linearity range, a rapid signal response time (within 100 s) and the detection limit is as low as 13 nM. In addition, the ability of the probe to detect thiophenols in living cells (HepG2 cells) via an enhancement of the fluorescence has also been proved.

•A green turn on fluorescent probe for biothiols in solution was developed.•The detection limit is as low as 10−8 M.•The probe can be applied in bioimaging.With the biological importance of biothiols, the development of probes for thiols has been an active research area in recent years. Here, we report a novel thiol-reactive fluorescent probe based on Michael addition reaction for selectively detecting thiols over other relevant biological species. The thiol adduct was characterized using NMR and mass spectroscopy and detection mechanism was further confirmed. This sensor with excellent selectivity for biothiols over other amino acids features a rapid signal response time, a good linearity range and a low detection limit. For the practical application of the sensor, it can be used to monitor thiol in live cells with turn-on fluorescence imaging.Based on the Michael addition reaction of thiol with the CC bond under mild conditions, we herein report a new fluorescent probe which features a rapid signal response time, a good linearity range and a low detection limit. The potential application of this new fluorescent probe was demonstrated by fluorescent imaging of thiol in living cells.

•The probe displayed excellent water solubility which could detect pH in aqueous solution.•The probe can be applied in bioimaging in living cells.•The distinct color changes promoted probe to be used for precise pH paper preparation.To obtain a better insight into the physiological and pathological functions of pH, probes with supra optical properties in water are still needed urgently. Focused on this situation, we herein reported a hemicyanine based probe for pH detection in aqueous solution. The probe has excellent water-solubility, high selectivity and sensitivity. Also, the structure of the probe from phenol to phenoxide induced a turn-on fluorescent response within a certain pH range of 4.5–10.7 and peaked with 30-fold enhancement, and the pKa value was determined to be 8.5. Simultaneously with the pH increase, a prominent solution color of the system changed from yellow to amaranth. More importantly, the biological experiments demonstrated the applicable of the probe to monitor the pH changes in living cells. This work illustrates that the probe could be practical and ideal pH indicator with good biological significance.Connected vanilline with benzoindoles moiety, we developed a novel pH probe which featured turn-on fluorescent responses and distinct color changes from yellow to amaranth within the pH range of 4.5–9.7 in aqueous solution. The probe has excellent water-solubility and high selectivity and sensitivity. Also, the probe could be used to monitor pH changes in living cells.

Correction for ‘An ICT based ultraselective and sensitive fluorescent probe for detection of HClO in living cells’ by Yongkang Yue et al., RSC Adv., 2015, 5, 77670–77672.

•Two new fluorescent probes for hypochlorite were developed.•The detection could be realized in quasi-aqueous phase with low detection.•The probe could be used to monitor intracellular ClO− in HepG2 cells.In this work, two high selective and sensitive fluorescent probes for ClO−, 7-Hydroxycoumarin and 4-Hydroxycoumarin were designed. The reaction mechanism that we speculated was the oxidized ring opening reaction and hydrolysis. The detection could be realized in quasi-aqueous phase and the detection limits of probe [7] and probe [4] for ClO− were found to be 56.8 nM and 70.5 nM. Furthermore, the probes can be used to cell imagings.

•1,8-naphthalimide-based probe bearing maleimide group was synthesized.•The compound exhibits highly selective recognition of thiol over other amino acids with fast response.•Its potential application to bioimaging was also illustrated.Up to date, the design of highly selective and fast response probes for Cys, Hcy, and GSH is still a challenge and very few examples have been reported so far. In this study, we synthesized a 1,8-naphthalimide-based probe bearing maleimide group to selectively detect thiol. After introduce thiol, the fluorescence intensity of probe showed significant enhancement, but other amino acids did not generate any change. The kinetic study showed that the reaction was complete within 120 s for Cys, Hcy and GSH, indicating that probe reacts rapidly with thiol under the experimental conditions. Furthermore, the ability of probe to detect thiol in living cells via an enhancement of the fluorescence was proved.1,8-naphthalimide-based probe bearing maleimide group was synthesized to selectively detect thiol with fast response. The detection limit was found to be as low as 0.045 μmol/L. Its potential application to bioimaging was also illustrated.

•We designed and synthesized a new chromene derivative.•The probe can specially recognize Cys.•The ability of probe to detect Cys in living cells was proved.A turn-on fluorescent probe for specific detection of cysteine (Cys) was developed based on the thiol-chromene click chemistry. Because of the relatively strong nucleophilic reactivity of SH of Cys compared with Hcy and GSH, this chromene derivate displayed excellent selectivity for Cys. The chromene derivate (probe 1) displayed non-fluorescent emission in DMSO/HEPES (v/v, 1:1, pH 7.4) system. However, the nucleophilic attack of Cys to the α,β-unsaturated ketone in probe 1 induced a 10 fold fluorescent emission enhancement at 515 nm. With the excellent properties including rapid, high selectivity and sensitivity toward Cys in aqueous solution, probe 1 was promoted to detect Cys quantitatively. The detection limit of this probe for Cys was found to be 64 nmol/L. The further bioimaging experiment of intracellular Cys detection by this probe was successfully applied in living cells, indicating that this probe holds great potential for biological applications.Based on the thiol ‘click’ chromene ring-open reaction, we designed and synthesized a chromene derivative as turn-on fluorescent probe for the Cys detection. With high sensitivity and selectivity, the probe could be used for intracellular Cys detection and bioimaging.

•We have developed two new colorimetric and fluorescent probes for hypochlorite based on a novel recognition mechanism: amido oxidized nitroso-group by hypochlorites.•The optical properties of the probe 2 and its ClO−-addition product were studied based on DFT and TDDFT were explored at the m062x/6-31+G (d) level.•The probe 2 could be applied in practical applications such as detecting the hypochlorite concentration of sodium hypochlorite disinfectant and bioimagings.We have developed two new colorimetric and fluorescent probes for hypochlorite based on a novel recognition mechanism: amido oxidized nitroso-group by hypochlorites, which realized the preparation of nitroso compounds. Furthermore, 1H NMR, ESI-MS and theoretical calculation proved the recognition mechanism. In addition, the probe 2 was applied in practical applications such as detecting the hypochlorite concentration of sodium hypochlorite disinfectant and bioimagings.In this study, we have developed two new colorimetric and fluorescent probes for hypochlorite based on a novel recognition mechanism: amido oxidized nitroso-group by hypochlorites, which realized the preparation of nitroso compounds. Furthermore, 1H NMR, ESI-MS and TD-DFT calculations proved the novel recognition mechanism. In addition, the probe 2 was applied in practical applications such as detecting the hypochlorite concentration of sodium hypochlorite disinfectant and bioimagings.

•Two “turn-on” fluorescent probes, which are conveniently prepared were presented.•Two probes showed high selective and sensitive recognition for ClO−.•The mechanism was proved by 1H NMR and ESI-MS.In this work, 2-naphthol (1) and its derivative 1-(2-hydroxynaphthalen-1-yl)naphthalen-2-ol (BINOL) (2) as two ratiometric fluorescence probes are used to detect hypochlorite, which is one of the biologically important reactive oxygen species (ROS), by UV–vis and fluorescent spectrometers. The fluorescence intensity of probe 1 and 2 were gradually decreased when addition of ClO−. Also, the detailed signal mechanism was elucidated by 1H NMR and ESI-MS. In addition, the detection limits of probe 1 and 2 for ClO− were found to be 81 nM and 49 nM. Both two probes showed high selectivity for hypochlorite.In this study, we have developed two ratiometric fluorescence probes based on 2-naphthol and its derivative BINOL for the detection of ClO− over other analytes. We speculate the mechanism is based on a specific reaction promoted by hypochlorite: probe 1 and probe 2 can undertake intermolecular dehydration reaction in the presence of hypochlorite. In order to elucidate the detailed signal mechanism, 1H NMR and ESI-MS were carried out. In addition, the detection limits of probe 1 and 2 for ClO− were found to be 81 nM and 49 nM. Both two probes showed high selectivity for hypochlorite.

•Based on thiol nucleophilic substitution fluorescent probe was synthesized.•The compound exhibits highly selective recognition of thiol over other amino acids.•Its potential application in bioimaging was also illustrated.Herein we report a highly selective thiol-reactive fluorescent probe based on a nucleophilic substitution reaction for detecting thiols over other relevant biological species. The probe, triphenylamine as a fluorophore and 2,4-dinitrobenzenesulfonyl chloride as a nucleophilic substitution group was synthesized and characterized. The ability to specially recognizing thiol was investigated by UV–vis and fluorescence spectrometers. Among the tested amino acids, only Cys, Hcy and GSH could turn on the fluorescence emission. It suggested that the system was a highly selective sensor for thiols. More importantly, the compound features a good linearity range and the detection limit is as low as 10−8 mol/L. In addition, as a typical biological thiol, the ability of probe to detecting Cys in living cells (HepG2 cells) via an enhancement of the fluorescence was proved.

•This off-on fluorescent probe can specifically detect cysteine.•The interaction between probe 1 and Cys in solution was studied in detailed.•The probe can be applied in bioimaging.Developing effective methods to specifically detect and image cysteine in vivo has become an increasingly important area of research. Here, we synthesized and characterized two isomers of 1,8-Naphthalimide derivatives (1 and 2), and result showed 1 is a fluorescent probe for selectively detecting cysteine over other relevant biological species based on Michael addition reaction. 1 can detect cysteine by fluorescence spectrometry with a detection limit of 0.064 μmol/L and can be used for detection of cysteine in living cells. The Michael addition mechanism of the reaction between 1 and cysteine was confirmed by MS and NMR spectra.Based on the Michael addition reaction of thiol with the CC bond under mild conditions, we herein report a new Cys fluorescent probe which features a rapid signal response time, a good linearity range and a low detection limit. The potential application of this new fluorescent probe was demonstrated by fluorescent imaging of Cys in living cells.

•The compound, N-[4-Methylcoumarin-7-yl]maleimide was firstly synthesized.•The compound exhibits highly selective recognition of cysteine over Hcy and GSH.•Its potential application to bioimaging was also illustrated.Up to date, the design of highly selective probes for Cys, Hcy, and GSH is still a challenge and very few examples have been reported so far. In this work, the compound, N-[4-Methylcoumarin-7-yl] maleimide was synthesized and it can specially recognize on Cys as an ‘OFF–ON’ fluorescent probe. For specific recognition on Cys of probe depends on its maleimide group, the structural and acidic differences of biothiol itself. Furthermore, the ability of probe to detect Cys in living cells (HepG2 cells) via an enhancement of the fluorescence was proved.N-[4-Methylcoumarin-7-yl]maleimide was firstly to be developed as a probe which exhibits highly selective recognition of cysteine. The detection limit was found to be as low as 74 nmol/L. Its potential application to bioimaging was also illustrated.

A new near-infrared (NIR) sensitive Cys/Hcy probe based on squaraine was rationally designed and synthesized. This is a Cys/Hcy sensor with excitation in the near-infrared region and features excellent selectivity for Cys/Hcy over other amino acids and GSH.

Phenolphthalein aldehyde was synthesized and used as a turn-on fluorescent probe for the detection of holmium ion (Ho3+), which is one of the lanthanide ions, in HEPES–DMF = 1:1 (v/v, pH = 7.4) solution with an excellent selectivity and sensitivity for Ho3+ over other metal ions.

An ICT based ultraselective and sensitive probe for colorimetric and fluorescent detection of HClO via oxidative cleavage of an alkene linker to epoxide and then to aldehydes was developed through the conjugation of pyridinium with vanilline.

A fluorescent probe has been synthesized and characterized as a selective and sensitive sensor for thiol detection. The probe exhibits a rapid response and high sensitivity to thiols in HEPES:DMF = 1:1 (v/v pH = 7.0) solution. The practical utility of the probe was demonstrated by its application to the detection of thiols in living cells.

Disperse Violet 26 is a commercially available fluorochrome used as an on–off fluorescent probe for the detection of ClO−, which is one of the biologically important reactive oxygen species (ROS), in HEPES:CH3CN = 1:1 (v/v pH = 7.0) with an excellent selectivity and sensitivity for ClO− compared to other analytes.

•A new compound, 2-quinolinone derivative was designed, synthesized and characterized.•Its selective recognition ability on Hg2+ was firstly studied by fluorescence and UV–vis spectroscopies.•The detection mechanism was explored by ESI-MS and 1H NMR analysis.A new compound based on 2-quinolinone derivative with very little side effects on organisms, 3-(1H-benzo[d]imidazol-2-yl)-6,7-difluoroquinolin-2(1H)-one, has been designed, synthesized and characterized. And its recognition ability was firstly studied by spectroscopy. The result indicated that the compound shows high selectivity for Hg2+ over other metal ions with detectable fluorescent signals in aqueous-methanol media. The proposed mechanism is that the fluorescence of the probe was quenched due to the effect from spin–orbit coupling of Hg2+ after the probe coordinated with Hg2+, and was proved by ESI-MS and 1H NMR analysis.Graphical abstract

Fluorol Red GK was developed as a on-off fluorescent probe of Au3+ based on Au3+ coordinating to cyano of probe, resulting in fluorescence quenching in a mixed aqueous environment, which was successfully applied to fluorescence imaging in living cells.

The commercially available fluorescent probe, 1,8-diamino naphthalene with a naphthalene ring as a chromophore and two amino groups as binding sites has been developed for sensitive detection of copper ions by fluorescence spectrometer in aqueous solution. It displayed an excellent selectivity and sensitivity for Cu2+ over other metal ions. The mechanism is that the fluorescence of probe was quenched by the paramagnetic effect from spin–orbit coupling of the Cu2+ after probe coordinated with Cu2+, and mechanism was proved by ESI-MS. The probe can be used to react to Cu2+ in live cells, providing a potentially powerful approach for probing Cu2+ chemistry in biological system.The commercially available fluorescent probe with a naphthalene ring as a chromophore and two amino groups as binding sites has been developed for sensitive detection of copper ions in aqueous solution. It displayed an excellent selectivity and sensitivity for Cu2+ over other metal ions, and mechanism was proved by ESI-MS. The probe can be used to react to Cu2+ in live cells, providing a potentially powerful approach for probing Cu2+ chemistry in biological system.

The salicylaldehyde derivative, 9-formyl-8-hydroxyjulolidine was developed as a fluorescent probe to detect weak acid ions. With the salicylaldehyde moiety as the chromophore, the probe exhibits pH sensitive detection of hydrogen sulfide and silicate in aqueous solution. It displays an excellent selectivity for hydrogen sulfide and silicate over other weak acid salts. Time-dependent density functional theory calculations confirmed that the fluorescence turn-on mechanism involved blocking intramolecular charge transfer. The probe detects S2− in live cells, providing a powerful method to study H2S chemistry in biological systems.9-Formyl-8-hydroxyjulolidine, with the salicylaldehyde moiety as the chromophore, was developed as a fluorescent probe to detect hydrogen sulfide and silicate in aqueous solution. Time-dependent density functional theory calculations confirmed that the fluorescence turn-on mechanism involved blocking intramolecular charge transfer. The probe detects S2− in live cells, providing a powerful method to study H2S chemistry in biological systems.

•We synthesized and characterized a new coumarin-based chromene derivative.•The optical properties of the probe and its Cys-addition product were theoretically studied.•The ability of probe to detect thiols in living cells was proved.•The probe was applied in direct determination of biorelevant thiols in human plasma.The synthesis and characterization of a coumarin–chromene (8, 9-dihydro-2H-cyclopenta[b]pyrano[2,3-f]chromene-2,10(7aH)-dione) (1) derivative and its use for thiol chemosensing in water was reported. Experimental details showed 1 acts as a probe for the detection of thiols including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), whereas amino acids which do not contain thiols induced no changes in UV–vis spectra and fluorescence emission properties of 1. A possible detection mechanism is a nucleophilic attack of thiols to the α,β-unsaturated ketone in 1 that resulted in a fluorescent coumarin derivative. Further studies showed that 1-thiol derivatives can be applied to the design of regenerative chemodosimeters for Cu2+, Hg2+ and Cd2+ in water based on Mn+-promoted desulfurization and recovery of 1. Furthermore, the optical properties of the probe and its Cys-addition product were theoretically studied. The ability of probe 1 to detect thiols in living cells (HepG2 cells) via an enhancement of the fluorescence was proved. Moreover, the applicability of 1 for the direct determination of biorelevant thiols in a complex matrix such as human plasma was also demonstrated.Graphical abstractCoumarin–chromene was firstly prepared and characterized. It displayed an excellent selectively and sensitivity for thiols by thiol ‘click’ chromene ring-open reaction on UV–vis and fluorescene spectra, which was rationalized by TDDFT calculation. The probe was applied in heavy metal ions regenerative chemodosimeter and bioimaging.

•Three isomers of rhodamine derivative were synthesized and fully characterized.•Compound 1 can recognize Cu2+.•The probe is a fluorescence probe thus can be applied in bioimaging.Three isomers of rhodamine derivative, ortho-pyridylaldehyde rhodamine hydrazone (1), meta-pyridylaldehyde rhodamine hydrazone (2), and para-pyridylaldehyde rhodamine hydrazone (3) were synthesized and characterized. And their recognition abilities for Cu2+ were studied by UV–Vis spectra. The result showed that ortho-pyridylaldehyde rhodamine hydrazone (1) due to having a suitable space coordination structure is a best selective probe for Cu2+ over other metal ions in 10 mmol/L HEPES buffer, pH 7.0/CH3OH (v/v, 1:1), and that it is a quick colorimetric and lagged fluorometric dual-model probe for Cu2+. Because it is a fluorescence turn-on probe, cell experiments show probe can permeate through cell membranes and react to Cu2+ within living cells.Three isomers of rhodamine derivative, ortho-pyridylaldehyde rhodamine hydrazone (1), meta-pyridylaldehyde rhodamine hydrazone (2), and para-pyridylaldehyde rhodamine hydrazone (3) were synthesized and characterized. And their recognition abilities for Cu2+ were studied. The result showed that ortho-pyridylaldehyde rhodamine hydrazone (1) is best probe for Cu2+, furthermore 1 is a colorimetric and fluorometric dual-model probe for Cu2+. It was also applied in bioimaging.

An ultraviolet–visible light (UV–Vis)-reversible but fluorescence-irreversible chemosensor was developed for the detection of copper. Coordination between the probe, 2-pyridylaldehyde fluorescein hydrazone (FHP), and Cu2+ gave a reversible UV–Vis response, Storage of the probe–Cu complex resulted in hydrolytic cleavage of the N═C bond, which released the fluorophore (ring-opened fluorescein hydrazine) and gave irreversible fluorescence. Thus, FHP becomes a multifunctional chemosensor, and its reversibility can be controlled by the reaction time. Cu2+ in living cells could be detected using FHP and general fluorescence methods.

A simple aldehyde-functionalized coumarin (7-diethylaminocoumarin-3-aldehyde) was utilized for the selective detection of bisulfite anions in water. The probe has exhibited a selective and sensitive response to the bisulfite anion against other anions, including Cys, through the nucleophilic addition of the bisulfite to probe. The fluorescence of the probe changes upon the addition of bisulfite anions, such that millimolar concentrations of bisulfite are detectable. Moreover, the sensor can also be applied to detect the level of bisulfite in sugar samples.A simple aldehyde-functionalized coumarin (7-diethylaminocoumarin-3-aldehyde) was utilized for the selective detection of bisulfite anions in water. The probe has exhibited a selective and sensitive response to the bisulfite anion against other anions, including Cys, through the nucleophilic addition of the bisulfite to probe. The fluorescence of the probe changes upon the addition of bisulfite anions, such that millimolar concentrations of bisulfite are detectable. Moreover, the sensor can also be applied to detect the level of bisulfite in sugar samples.

A fluorescein derivative, 2-pyridylaldehyde fluorescein hydrazone (FHP), was developed for detection of hypochlorites. This probe functioned by oxidizing Cu+ to Cu2+ to form a Cu2+ complex, which produced colorimetric and fluorescent signals that were monitored by ultraviolet–visible and fluorescence spectrophotometry, respectively. Other common anions, including F−, Cl−, ClO3−, NO2−, CN−, S2−, SCN−, P2O74−, AcO−, CO32−, SO42−, ClO4−, did not interfere with the hypochlorite detection, and hypochlorites could be detected at low micromolar levels in aqueous solutions. The color change on reaction with hypochlorites was rapid and visible to the naked eye. The sensor could be applied to the detection of hypochlorites tap water.

A strategy for the determination of the presence of thiol-containing amino acids was successfully established by simply assembling copper chloride and xylenol orange (3,3′-bis[N,N-bis(carboxymethyl)aminomethyl]-o-cresolsulfonephthalein trisodium salt; XO) in a 1:1 molar ratio in quasi-physiological water solution (pH 6.0). The copper(II)–XO ensemble was highly selective for thiol species such as cysteine, homocysteine, and glutathione without interference from other amino acids and could quantitatively detect thiol in the range from 10 to 200 μM with a linear relationship having an average molar absorbance constant of 6530 L mol −1 cm −1 in pure water. The whole recognition process for thiol gave rise to a rapid visual color change from purple-red to yellow which can be observed simultaneously with the naked-eye.

A regenerative, molecular machine-like “ON−OFF−ON” chemosensor based on a chromene molecule with the pyran ring “OFF−ON−OFF” cycle is reported for the first time. It behaves as a molecular lock that requires a thiol “key” to open the lock and a mercury(II) ion “hand” that unlatches the key for unsheathing the key to close the lock.

A novel strategy for the determination of oxalate anions was successfully established using a copper ion and pyrocatechol violet (PV) ensemble. The sensor ensemble can discriminate oxalate over other common anions including F−, Cl−, I−, Br−, HPO42−, PO43−, AcO−, CO32−, SO42−, ClO4−, P2O74−, S2− (deposited by Ag+), CN− (shielded by Fe3+) and can detect oxalate at low microgram levels in quasi-physiological aqueous solutions. The detection of the oxalate anion gives rise to a rapid observable visual color change from blue to yellow.

The optical properties of a novel, rhodamine-based derivative, synthesized by reacting rhodamine hydrazide and 5-chlorosalicylaldehyde in ethanol, were investigated in methanol:HEPES solution. The novel sensor displayed selectivity for Cu2+, as evidenced by a colourless to dark red colour change, which was characterized using UV–visible spectroscopy and which also allowed visual detection of Cu2+. In contrast, selectivity towards VO2+ was determined from changes in the emission spectra in the nanomolar range. This represents the first reported rhodamine-based sensor capable of detecting both Cu2+ and VO2+ using two different modes.

A kind of complex of CeTTA4 · HP (TTA = 2-[(Trifluoroaceto)aceto]thinophene, HP = piperidine) has been synthesized and characterized, and its DNA-binding properties of CeTTA4 · HP using UV spectra, fluorescent spectra, thermal denaturation, viscometry, molecular modeling and CV (cyclic voltammetry). The results show that the binding-mode between CeTTA4 · HP and DNA is intercalation. The interaction between the complex and DNA has also been investigated by gel electrophoresis. Interestingly, we found that the CeTTA4 · HP complex can cleave circular plasmid pBR322 DNA at pH 7.2 and 37°C. In addition, BDNPP was chosen (bis(2,4-dinitrophenyl)-phosphate) as a model compound to further study its cleavage mechanism for pBR322 DNA. From the first-order kinetics equation, we prove indirectly the mechanism may be hydrolytic cleavage.

A new thiol-containing colorimetric probe has been developed by using a chromene derivative, 7-nitro-2,3-dihydro-1H-cyclopenta[b]chromen-1-one (1). The molecule exhibited high selectivity and sensitivity for detecting thiol species as cysteine, homocysteine, and glutathione in aqueous solution through a rapid visual color change from colorless to yellow.

The sulfide anion is significant in industrial processes, biology and environmental science. Hence, robust fluorescent sensors for sulfide which are water soluble and biocompatible are highly desirable. Here, we developed a novel red-emitting fluorescent probe (SP1) for the sulfide anion based on cleaving the dinitrobenzenesulfonate ester to restore the fluorescence, accompanied by a long wavelength emission at 644 nm. The detection process took place in 100% PBS buffer, which suggested it had excellent water solubility. Most importantly, the ability of SP1 to detect sulfide anions in living cells (MCF-7 cells) and zebrafish has also been proven.

A fluorescent probe has been synthesized and characterized as a selective and sensitive sensor for thiol detection. The probe exhibits a rapid response and high sensitivity to thiols in HEPES:DMF = 1:1 (v/v pH = 7.0) solution. The practical utility of the probe was demonstrated by its application to the detection of thiols in living cells.

The reaction of salicylhydroxamic acid with hypochlorite produces 1,2-benzisoxazoline-3-one, a heterocycle that contains a fluorophore. As a result, this reaction was used as the basis for a new, selective and sensitive fluorescence system for the recognition of hypochlorite. The effectiveness of the method was demonstrated by its use to detect hypochlorite in a disinfectant solution as well as to image hypochlorite in cells.