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Ferric ion (Fe3+) serves as an essential and indispensable inorganic element in various biological process. Excess Fe3+ is harmful for biological systems and human health. Herein, highly sensitive carbon quantum dots (Fe-CQDs) for ferric ions were synthesized by a high-efficiency, one-step hydrothermal route utilizing L-arginine and citric acid. The prepared Fe-CQDs exhibited good water solubility, high photostability, and bright blue florescence with relatively high quantum yields (QYs) over 21.33% and a Stokes shift exceeding 100 nm. The functionalized Fe-CQDs offer rapid, sensitive, and selective recognition of Fe3+ with a linear relationship from 0.6 to 80 μM and a low detection limit of 0.2 μM. Moreover, the synthesized Fe-CQDs illustrated strong anti-interference properties in samples and buffer solutions. The developed sensor demonstrated high biocompatibility and was successfully applied for intracellular Fe3+ determination in SHSY5Y and HT22 cells, illustrating excellent imaging application. The present work provides a promising platform for the early clinical diagnosis of Fe3+-associated diseases. [ABSTRACT FROM AUTHOR]

Given the important role of carboxylesterase 2 (CES2) in the metabolism of various esters, it is of significance to develop a tool to determine endogenous CES2 activity in a rapid and highly selective manner. In this work, an "off-on" rhodamine-based fluorescent probe is reported as an effective tool for CES2 activity. Based on the substrate recognition preference of CES2 (large alcohol and small acyl groups), the probe with dimethyl carbamate as the recognition group performs well in terms of selectivity and sensitivity to CES2. The fluorescence switching control of the probe for CES2 was achieved by using the spirolactone structure of rhodamine. The probe shows the fast generation of a fluorescence signal at 634 nm upon hydrolysis of CES2 with excitation at 578 nm. The results showed a linear relationship between the fluorescence intensity at 634 nm and the CES2 activity from 0 to 4 μg/mL. The probe reacts rapidly with CES2, and the reaction is stable within 40 minutes. The probe is highly selective for CES2, with a detection limit as low as 0.303 μg/mL. In addition, the probe has currently been successfully utilized to evaluate CES2 activity in living cells. Hence, this probe is anticipated to be significant in identifying endogenous CES2 activity in intricate biological settings. [ABSTRACT FROM AUTHOR]

Metal cations such as Zn2+, Al3+, Hg2+, Cd2+, Sn2+, Fe2+, Fe3+ and Cu2+ play important roles in biology, medicine, and the environment. However, when these are not maintained in proper concentration, they can be lethal to life. Therefore, selective sensing of metal cations is of great importance in understanding various metabolic processes, disease diagnosis, checking the purity of environmental samples, and detecting toxic analytes. Schiff base probes have been largely used in designing fluorescent sensors for sensing metal ions because of their easy processing, availability, fast response time, and low detection limit. Herein, an in-depth report on metal ions recognition by some Schiff base fluorescent sensors, their sensing mechanism, their practical applicability in cell imaging, building logic gates, and analysis of real-life samples has been presented. The metal ions having biological, industrial, and environmental significance are targeted. The compiled information is expected to prove beneficial in designing and synthesis of the related Schiff base fluorescent sensors. [ABSTRACT FROM AUTHOR]

Endogenous sulfur dioxide (SO2), as a gas signal molecule, has a certain physiological functions. Understanding the role of endogenous SO2 in human physiology and pathology is of great significance to the biological characteristics of SO2,which bring challenges to develop fluorescent probes with excellent performance. Herein, we rationally designed and constructed a novel near-infrared bioprobe benzaldehyde-benzopyrylium (BBp) by employing the nucleophilic addition benzopyrylium perchlorate fluorophore and benzaldehyde moiety by means of C = C/C = O group that serves as both fluorescence reporting unit. Probe BBp exhibit excellent sensing performance with fluorescent "On − Off"rapid response (100 s) and long-wavelength emission (670 nm). With the treatment of HSO3−, the color of BBp solution obviously varies from purple to colorless, and the fluorescent color varies from red to colorless. By the fluorescence and colorimetric changes, probe BBp was capable of sensitive determination HSO3− with low limits of detection (LOD) of 0.43 μM, realizing visual quantitative monitoring SO2 derivative levels. Due to the low phototoxicity and good biocompatibility, it was successfully applied to monitor SO2 derivatives and fluorescence imaging in HepG2 and HeLa living cells. Hopefully, this work supplies a new strategy for designing NIR fluorescent probes for quantitative determination SO2 derivatives in biological samples. [ABSTRACT FROM AUTHOR]

Hypochlorite plays a vital role in biological systems and our daily life. The rapid and convenient detection of hypochlorite is imperative and significant for disease treatment and human health. In this work, EY/UiO-66-NH2 (EY = eosin Y) was prepared through a hydrothermal process and could be applied to the detection and bioimaging of hypochlorite as a self-calibrating sensing nanoprobe. EY/UiO-66-NH2 features two emissions at 432 nm and 533 nm, and the emission intensity of 533 nm is enhanced with increasing ClO− concentration. EY/UiO-66-NH2 could be utilized as a ratiometric fluorescence sensor of ClO−. The linear range of EY/UiO-66-NH2 towards ClO− is 0.1–200 μM and its detection limit is 46.4 nM. In comparison with previously reported probes for ClO−, EY/UiO-66-NH2 has the advantages of a wide linear range, low detection limit, turn-on fluorescence and ratiometric response. This work provides a new method for ClO− detection in living cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two rhodamine derivatives (L-Et and L-Pr) were developed without imine bond to avoid hydrolysis for Al3+ sensing with high selectivity. • There were significant increments in fluorescence at 555 nm and absorbance at 530 nm of with Al3+. • LOD values for Al3+ were determined ∼1.0 nM. • Both of these probes were used to image the cation in C6 cells. To address limitations like susceptibility to hydrolysis of an imine bond and low selectivity of rhodamine based chemosensors, we report here two rhodamine dyes, namely, L-Et i.e. 3′,6′-bis(ethylamino)-2′,7′-dimethyl-2-(2-morpholinoethyl)spiro[ isoindoline -1,9′- xanthen ]-3-one and L-Pr i.e. 3′,6′-bis(ethylamino)-2′,7′-dimethyl-2-(3-morpholinopropyl)spiro[ isoindoline -1,9′- xanthen ]-3-one for detection of Al3+ in 10 mM HEPES buffer in H 2 O/EtOH = 1:9 (v/v) (pH 7.4). Both the probes detect exclusively Al3+ among 16 different metal ions. The sensing ability has been achieved by noting color change (colorless to pink), increment in absorption intensity at 530 nm and fluorescence intensity at 555 nm. Opening of spirolactam ring of the chemosensors followed by complexation with Al3+ is responsible for such changes. A 1:1 complex is formed by both the probes with high association constant (1.14 × 105 M−1 for L-Et and 1.17 × 105 M−1 for L-Pr). The limit of detection values of L-Et and L-Pr towards Al3+ have been determined as 1.7 nM and 1.1 nM, respectively signifying very high sensitivity. These have been successfully applied in cell imaging studies in C6 cells. Introduction of a methylene group does not influence spectral properties vividly. As both the probes do not contain any imine bond, the possibility of hydrolysis in the presence of Al3+ has been avoided. [ABSTRACT FROM AUTHOR]

Determining the activity of lysosomal β-hexosaminidase in cells is of great importance for understanding the roles that these enzymes play in pathophysiological events. Herein, we designed the new fluorescent probe, βGalNAc-Rhod-CM(NEt 2), which consisted of a βGalNAc-linked rhodol unit serving as a β-hexosaminidase reactive fluorogenic moiety and a N,N′ -diethylaminocoumarin (CM(NEt 2)) group acting as a fluorescence marker for determining the degree of cell permeabilization. Treatment of βGalNAc-Rhod-CM(NEt 2) with β-hexosaminidase promoted generation of Rhod-CM(NEt 2), thereby leading to an increase in the intensity of fluorescence of Rhod. However, this probe did not respond to the functionally related glycosidase, O-GlcNAcase. The detection limit of βGalNAc-Rhod-CM(NEt 2) for β-hexosaminidase was determined to be 0.52 nM, indicating that it has high sensitivity for this enzyme. Furthermore, the probe functioned as an excellent fluorogenic substrate for β-hexosaminidase with k cat and K m values of 17 sec−1 and 22 μM, respectively. The results of cell studies using βGalNAc-Rhod-CM(NEt 2) showed that levels of β-hexosaminidase activity in cells can be determined by measuring the intensity of fluorescence arising from Rhod and that the intensity of fluorescence of CM(NEt 2) can be employed to determine the degree of cell permeabilization of the probe. Utilizing the new probe, we assessed β-hexosaminidase activities in several types of cells and evaluated the effect of glucose concentrations in culture media on the activity of this enzyme. [Display omitted] • Development of the sensitive and selective fluorescent probe for β-hexosaminidase. • Determination of levels of β-hexosaminidase activities in several types of cells. • Evaluation of effect of glucose concentrations in media on β-hexosaminidase activity. [ABSTRACT FROM AUTHOR]

The utilization of nanomaterial-based probes in detecting glutathione (GSH) and cell imaging has aroused extensive attention owing to the excellent properties of nanoprobes. Herein, we have synthesized manganese dioxide-S, O co-doped graphitic carbon nitride quantum dots (MnO2-S, O-CNQDs) nanocomposite by in situ synthesis of MnO2 nanosheets in S,O-CNQDs dispersion solution. It was found that GSH could specifically bind to MnO2-S, O-CNQDs so that the fluorescence of S, O-CNQDs could be recovered. As such, a "turn-on" MnO2-S, O-CNQDs nanoprobe can be fabricated and applied to rapidly determine trace amounts of GSH. Under the optimal conditions, MnO2-S, O-CNQDs shows sensitive response to GSH in the range 10–270 μM with a detection limit of 0.307 μM (S/N = 3). The developed MnO2-S, O-CNQDs probe has demonstrated great potential to detection of GSH in biological samples and glutathione injections. What is more, MTT assay indicates that MnO2-S, O-CNQDs has low biotoxicity. The non-fluorescence MnO2-S, O-CNQDs reacts with GSH to recover the fluorescence of S, O-CNQDs in HepG2 cells. Thus, the "turn-on" fluorescence change of MnO2-S, O-CNQDs offers a potentially useful tool to monitor GSH of cancer cells. [ABSTRACT FROM AUTHOR]

An easy prepared probe, BHMMP, was designed and synthesized, which displayed a significant fluorescence enhancement (over 38-fold) and obvious color change in the recognition of Al3+. The binding ratio of probe BHMMP to Al3+ was determined as 1:1, according to Job plot. The binding mechanism was fully clarified by the experiments, such as FT-IR spectrum, ESI–MS analysis, and 1H NMR titration. A DFT study further confirmed the binding mode of BHMMP to Al3+. The limit of detection (LOD) for Al3+ was determined as low as 0.70 µM, based on the fluorescence titration of BHMMP. Moreover, the results from real sample experiments, including real water samples, test papers, and cell images, well-demonstrated that BHMMP was capable of sensing Al3+ in environmental and biological systems. [ABSTRACT FROM AUTHOR]

Designing functionalized MOFs with specific reactivity and NIR photoelectrochemical and fluorescent response is critical for developing biosensing systems. Herein, SCy7, a conjugate macrocycle ligand with a specific fluorescence responsive group to HClO, was designed and synthesized. Responsive Nd-MOF nanorods were successfully prepared by using SCy7 as the organic ligand and Nd3+ as the metal central ion. Nd-MOF nanorods show good absorption characteristics in the wavelength range of 200–1200 nm with a band gap of 0.89 eV. Nd-MOF nanorods were employed as a photoactive material to construct a near-infrared photoelectrochemical cytosensor for MCF-7 cells by integrated with an aptamer. The photocurrent variation exhibits a good linear response to MCF-7 cells in the concentration range of 50–1.0 × 107 cells mL−1, and a comparatively low detection limit of 18 cells mL−1 (S/N = 3). The NIR PEC cytosensor was also employed for monitoring endogenous HClO released from MCF-7 cells as being stimulated by PMA. HClO is an electron acceptor that can convert the anodic photocurrent into cathodic photocurrent, thus achieving monitoring HClO through the conversion of photocurrent polarity. Furthermore, Nd-MOF was coated with F127 to improve its hydrophilicity and biocompatibility, and to provide a Nd-MOF@F127 with a fluorescence emission peak at 830 nm. Nd-MOF@F127 show specific fluorescence response to HClO, and thus was successfully used in imaging HClO variation in cells and breast cancer bearing mice. [Display omitted] • Nd-MOF nanorods with specific response to HClO were successfully synthesized. • A NIR PEC cytosensor based on Nd-MOF was developed for MCF-7 cells assaying. • Real-time monitoring HClO was achieved by photocurrent polarity conversion. • Fluorescence imaging HClO in cells and mice was performed by using Nd-MOF@F127. [ABSTRACT FROM AUTHOR]

A novel NIR probe based on oxazolonaphthoimidazo[1,2- a ]pyridine-malononitrile (ONIM) conjugate linked by vinyl linkage was designed and synthesized for the detection of cyanide ion. [Display omitted] • An orange emitting sensor ONIM (712 nm) with D-π-A framework is synthesized. • The ONIM emission is retained in the solid state. • ONIM could sense cyanide ion without interference of other anions. • Sensing mechanism of cyanide sensing was confirmed by 1H NMR and DFT calculations. • Live cell imaging in human breast cancer cell MDA-MB 231 and as solid state sensor was achieved. Cyanide is undoubtedly dangerous and fast acting chemical employed in various industrial applications with toxic side effects, which raises urgent need for its monitoring. In this context, oxazolonaphthoimidazo[1,2- a ]pyridine-malononitrile (ONIM) conjugate linked by vinyl linkage was designed, synthesized and characterised by FT-IR, NMR and mass spectrometry. The developed probe has been evaluated for the colorimetric and fluorometric detection of cyanide ion. An obvious color change with unique rapid " turn-off " fluorometric response was observed within 5 s upon addition of CN– thus reflecting its better acuteness and sensitivity over other competing anions. The developed probe exhibits a detection limit of 9.54 nM which is very low in comparison to maximum permitable amount of cyanide in drinking water (1.9 µM). The probe is stable within the p H range of 2–9 and suitable for the recognition of CN– in the p H range of 7 to 10, specially at neutral p H conditions. The chemodosimetric approach based detection mechanism was authenticated by 1H NMR titration and DFT calculations. The solid state applications were established by utilising ONIM impregnated TLC plates and filter paper in cyanide recognition. The solid state emissive behaviour of ONIM offers on-spot detection of the cyanide anion. Additionally, the practicability of ONIM has been extended in live cell imaging of CN– in human breast cancer cell (MDA-MB-231), which revealed a " turn-off " fluorescence response for the probe in the presence of CN– ion. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel Al3+ Schiff base probe JHK was designed and synthesized. • JHK has high selectivity, high fluorescence quantum yield and low detection limit for Al3+. • JHK was successfully applied to living cells and zebrafish. A novel fluorescent probe N'-(2-hydroxybenzylidene)-indole-3-formylhydrazine (JHK) was designed and synthesized based on the condensation reaction of indole-3-formylhydrazine and salicylaldehyde. The probe JHK solution could highly selectively recognize Al3+ by the obvious fluorescence enhancement (288-fold) after adding Al3+. And the probe solution with Al3+ had a very high fluorescence quantum yield (89.29 %). The detection limit was calculated to be 1.135 nM, which was significantly lower than many reported detection limits, indicating that the probe JHK had pretty good sensitivity. The ratio of JHK to Al3+ (1:1) and the sensing mechanism were determined by Job's plot, 1H NMR spectra, FTIR spectra, ESI-MS and Gaussian calculation. The probe solution and medium-speed filter paper were successfully used to make test papers for more convenient detection of Al3+. Furthermore, the probe JHK had been successfully applied to the detection of Al3+ in real water, zebrafish and living cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • The probe EDPH specializes in the detection of H 2 S with high selectivity, high sensitivity and good detection limits. • The probe EDPH has been shown to have applications in intracellular fluorescence imaging. • Purine-based fluorescent probes for the detection of H 2 S are a new direction. Hydrogen sulfide (H 2 S) is a gas with a toxic odor that plays an irreplaceable role in physiological activities within the mammalian body. Therefore, it is important to do the distribution and quantitative detection of H 2 S in mammalian cells. In this paper, a fluorescence probe (EDPH) based on purine scaffold was designed and synthesized with high sensitivity and good selectivity. H 2 S induced ether bond breakage in EDPH , resulting in a significant redshift of the absorption band (from 370 nm to 500 nm) with a Stokes shift of 130 nm. After the addition of H 2 S, the fluorescence intensity of EDPH showed a good linear correlation with the concentration of H 2 S, which enabled the quantitative detection of H 2 S with a low limit of detection (41 nM). Finally, the EDPH was applied to the cellular Hele, and the probe has good cellularity imaging capability for the detection of H 2 S in living systems. [ABSTRACT FROM AUTHOR]

The abnormally elevated expression level of glutathione (GSH) has been observed in various human cancer cells and tissue. Thus, effective methods for glutathione detection are of great importance in early diagnosis of cancer. However, many fluorescent probes for GSH detection suffer from the interference of the abundantly existent nucleophilic biomolecules in biological environment. In this work, we propose a sequential activation strategy to overcome this problem by designing and synthesizing a series of 1,3,5-triazinyl resorufin turn-on fluorescent probe (Probes 1–3). As two electrophilic sites are presented in probes, GSH sequentially reacts with the resorufin and the triazine moiety, resulting in significant fluorescence augmentation (up to 165.0-fold). Designed probes possess low limit of detection as low as 1.8 μM). Cellular fluorescent imaging has been successfully applied to selectively detect GSH in several living cells. [Display omitted] • Novel sequential activation strategy allows the Probe 1–3 to detect GSH with high selectivity. • Designed fluorescent probes exhibited strong fluorescence intensity as response. • Designed probes realized GSH visualization in multiple cells with high fidelity. [ABSTRACT FROM AUTHOR]

In this work, by installing a free-rotating benzene ring to suppress the intermolecular π–π stacking effect in the aggregated state, a naphthalimide-derived hypochlorite (ClO−) fluorescent probe, Probe A, with the aggregation-caused quenching (ACQ) effect was successfully transformed into Probe B possessing typical aggregation-induced emission (AIE) characteristics. The experimental results indicated that Probe B with good selectivity and a low detection limit (LOD) of 0.02 µM can also exhibit a significant ratiometric fluorescence color change from cyan to dark blue within 2 min in a nearly pure water solvent system after the addition of ClO−. Finally, by virtue of the good photophysical properties and ClO− sensing performance, Probe B and the Probe B loaded portable test paper were successfully applied to live cell imaging and the naked eye recognition of ClO−, respectively. [ABSTRACT FROM AUTHOR]

A general synthetic method was improved to synthesize a chemosensor based on a tripodal Bodipy (t-BODIPY) structure. The product and its intermediate products were successfully prepared and fully characterized. The metal ion sensing performance of the tripodal compound was evaluated by UV/Vis and fluorescence spectroscopies. According to the obtained data, t-BODIPY is a selective and sensitive fluorescence probe for detection of Cu2+ ions in the presence and in the absence of competing ions. This chemosensor presents relatively a low detection limit of 5.4 x10-7 M for Cu2+. Bio-imaging studies on living yeast cells suggest that t- BODIPY has some advantages over other chemosensors to recognize copper (II) ions. [ABSTRACT FROM AUTHOR]

Zinc ion is closely related to human health. Its content in human body is small, while the effect is large. However, it is not the more the better, must be in a scientific balance. Therefore, it is significant to the rapid detection of Zn2+ in the environment and organism. Herein, a fluorescent probe based on 2-hydroxy-1-naphthalene formaldehyde and furan-2-carbohydrazide was conveniently synthesized via Schiff base reaction. And this probe has been successfully applied to the accurate and quantitative detection of Zn2+ in real samples, showing turn on fluorescence, good selectivity, very low detection limit, real time response and reusability. In addition, this probe has the potential application to trace Zn2+ in living cells with low cytotoxicity. [ABSTRACT FROM AUTHOR]

[Display omitted] • An "off–on" long-wavelength fluorescent probe is synthesized for Cys detection. • The probe has a large Stokes shift (211 nm) and reacted with Cys specifically. • The probe can monitor Cys fluctuations caused by redox imbalance in HepG2 cells. • The probe can be used for fluorescence imaging in cells and mice. In this research, an "off–on" long-wavelength fluorescent probe (DCMN-Cl) based on (E)-2-(3-(2-(6-hydroxynaphthalen-2-yl)vinyl)-5,5-dimethylcyclohex-2-en-1-ylidene) malononitrile (DCMN) is designed and synthesized for cysteine (Cys) detection. DCMN-Cl exhibits a large Stokes shift (211 nm) and shows rapid response and high specificity to Cys. The fluorescence initensity at 635 nm reveals a good linear relationship with Cys concentration in the 0 to 50 μM range, and the detection limit is as low as 159 nM. The probe is also used for fluorescence imaging of Cys in cells and mice. Moreover, the probe provided visual evidence of Cu2+ and curcumin-induced intracellular Cys fluctuations. [ABSTRACT FROM AUTHOR]

In this work, two naphthalene scaffolds dangling around a benzene moiety as a colorimetric and fluorimetric probe for Fe3+ in aqueous media have been reported. Recognition processes of Fe3+ were shown to be scarcely influenced by other coexisting metal ions. The probe exhibits a turn on colorimetric and a turn off fluorimetric detection of Fe3+ ions. The association constant for sensor 1–Fe3+ complex was found as Ka = 1.12 × 105 M–1 with the detection limit of 1.7 nM. The chemosensor has been utilized for bioimaging of E. coli cells. [ABSTRACT FROM AUTHOR]

In this work, we synthesized a simple fluorescent probe, which can selectively detect cysteine. With addition of cysteine, the probe solution showed marked color change from pale yellow to orange color by naked eye. There was an excellent linear relationship between fluorescence intensity of probe and cysteine concentration. Moreover, the probe displayed satisfactory detection limit. Low toxicity and cellular imaging offered the important conditions for detecting cysteine in biological system. [ABSTRACT FROM AUTHOR]

A new fluorescence probe 1 for sulfur dioxide derivatives has been developed which acts through nucleophilic addition of the derivatives and shows high stability, specificity, and sensitivity. In the presence of SO2 derivatives, the fluorescence intensity of probe 1 significantly decreases within a short time period of 40 s, along with a low detection limit of 0.32 µM. Fluorescence imaging capability of probe 1 was also investigated, showing clear detection of SO2 derivatives in living cells. The results indicate that this probe has a great potential for the detection of SO2 derivatives in broad biological and relevant samples. [ABSTRACT FROM AUTHOR]

Nitro groups with a strong electron-withdrawing effect can powerfully influence the fluorescence of fluorophores. In this work, through adjusting the nitro group at the HBT fluorophore to construct a phenylhydrazone structure, two probes (HBTN and HBTH) were synthesized to detect OCl−. Consequently, HBTN with the nitro group quenched the fluorescence of HBT and HBTH without the nitro group causing a redshift of the fluorescence, which resulted in enhanced and ratiometric fluorescence signal changes during the detection process. Among them, HBTN shows good ability to selectively detect OCl− in the concentration range of 0–14 μM with the detection limit of 2.06 nM. Based on HBTN, a portable test strip for detecting OCl− was made for the convenient quantification of the OCl− concentration with a spectrophotometer, and exogenous and endogenous OCl− was successfully imaged in cells. [ABSTRACT FROM AUTHOR]

Fluorescent determinations of analytes have proven to be a powerful method due to their simplicity, low cost, detection limit, rapid photoluminescence response, and applicability to bioimaging. Fluorescence imaging as a powerful tool for monitoring biomolecules within the living systems. Schiff base has been extensively used as strongly absorbing and colorful chromophores in the design of chemosensors. In recent years, Schiff base based fluorescent probes have been developed for the detection of various toxic analytes and imaging of various analytes in biological systems. This review gives an overview of the important fluorescent sensors which are based on Schiff base, their approaches for molecular recognition, and their potential application in bioimaging studies. [ABSTRACT FROM AUTHOR]

Biothiols, including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play key roles in biological processes, and detecting such thiols selectively is critical for understanding functions of biothiols. In this work, a pyridazine annelated perylene–based fluorescent probe PAPC is synthesized for highly selective detection of Cys. PAPC exhibits strong blue emission in PBS, while the red emission at 605 nm can be observed in the presence of Cys. The probe PAPC shows ratiometric fluorescence (I605/I460) detection of Cys with wide linear range of 1–120 μM and low detection limit of 0.19 μM. Super large Stokes shift (170 nm) and ratiometric fluorescence endow the probe low background signal. The discrimination of Cys over Hcy and GSH can be achieved through the difference of the ratiometric fluorescence. In addition, the probe has been proven to track Cys in real samples such as urine and HeLa cells. Therefore, PAPC probe is a promising candidate for detecting Cys in practical application. [ABSTRACT FROM AUTHOR]

Nitroreductase (NTR) with a high expression level in tumors has been considered as a biomarker of highly aggressive hypoxia tumors. Thus, it is important to develop powerful tools for tumor hypoxia detection. Here, we developed a two-photon fluorescent probe hTP-NNO2 for NTR detection. The probe with one-step synthesis exhibited high yield. hTP-NNO2 showed high selectivity and sensitivity for NTR and the detection limit was as low as 43 ng mL−1. hTP-NNO2 also showed low cytotoxicity and high stability, indicating that hTP-NNO2 is suitable for NTR detection in real-time and in situ under physiological conditions. hTP-NNO2 was used for NTR imaging in hypoxia cells and the fluorescence intensity of hTP-NNO2 increased with decreasing oxygen concentration. Benefiting from the advantages of two-photon fluorescent probes, we performed NTR detection in deep brain tissue with an imaging depth of up to 100 μm. hTP-NNO2 was further successfully applied for NTR detection in zebrafish and tumors. These results indicated that we developed a promising fluorescence imaging tool for NTR detection in vitro and in vivo. [ABSTRACT FROM AUTHOR]

A multiple turn-on fluorophore (FHCS), combining fluorescein, hydrazone, cyanuric chloride and salicylaldehyde chromone into a molecule, was identified and developed based on density functional theoretical calculation. It was expected that FHCS could express exclusive fluorescent signals and improved Stokes shifts when chelating Al3+ or Zn2+. After it was synthesized and characterized in detail, it was noted that FHCS could turn-on fluorescently discriminate trace Al3+ and Zn2+ under the optimized conditions, i.e., from no-fluorescence to strong blue fluorescence for Al3+ and to green fluorescence for Zn2+ with low detection limits of 5.37 × 10−8 M and 7.90 × 10−8 M respectively. Owing to its low toxicity, FHCS was successfully applied for quantitative determination of Al3+ and Zn2+ in natural aqueous samples and toxicity evaluation of Al3+ and Zn2+ in living cells and bio-tissues with excellent linear relationships. The action mechanisms for FHCS with Al3+ and Zn2+ were confirmed to form stable 5-member-co-6-member condensed rings between Al3+/Zn2+ and N/O atoms in FHCS by both theoretic and experimental methods, which resulted in turn-on fluorescence with different dipolar moments and improved Stokes shifts. A multiple turn-on fluorophore, combining fluorescein, hydrazone, cyanuric chloride and salicylaldehyde chromone into a molecule (FHCS), was identified and developed for turn-on fluorescently discriminate trace Al3+ and Zn2+ in natural aqueous, living cells and bio-tissue samples with quite low detection limits of 5.37 × 10−8 M and 7.90 × 10−8 M respectively. The action mechanisms for FHCS with Al3+ and Zn2+ were confirmed by both theoretic and experimental methods to form stable 5-member-co-6-member condensed rings between Al3+/Zn2+ and N/O atoms, which resulted in turn-on fluorescence with different dipolar moments and improved Stokes shift. Image 1 • A multiple turn-on fluorophore combining fluorescein, hydrazone, cyanuric chloride and salicylaldehyde chromone was developed. • It could turn-on fluorescently monitor Al3+ and Zn2+ in aqueous. • It was applied for cell imaging of Al3+ and Zn2+ in bio-samples. • The reaction mechanism was to form stable 5-member-co-6-member condensed rings with improved Stokes shift. [ABSTRACT FROM AUTHOR]

Herein, a facile method to synthesize the fluorescence probe 1‐(4‐(1,5‐diphenyl‐4,5‐dihydro‐1H‐pyrazol‐3‐yl)phenyl)‐1H‐pyrrole‐2,5‐dione (probe 10) was reported. The relative quantum yield determined using quinine sulfate for the probe 10 is 42% in 100% acetonitrile (ACN), which was reduced to 6% in 10% ACN‐water system. The turn‐off probe 10 becomes turn‐on selectively in the presence of glutathione (GSH). The Probe 10 is highly sensitive to GSH in the presence of common interfering molecules like cysteine, N‐acetylcysteine, thioglycolic acid, mercaptoethanol, and mercaptopropionoic acid. The limit of detection is 0.06 μM. The practical use of the probe 10 was demonstrated through quantifying GSH (1.68 mM) in the blood serum of healthy person, artificial cerebrospinal fluid, and artificial urine. Probe 10 works on a wide range of pH 2–12. Cells expressing GSH can be imaged using probe 10 and also useful in analysing the percentage of GSH in the cells under oxidative stress. [ABSTRACT FROM AUTHOR]

In this paper, a novel chemosensor (named L1) for Fe3+ based on the rhodamine 6G and o-vanillin has been synthesized, which can selectively recognize Fe3+. The L1 solution showed a distinguishable colour change by naked eye, and the fluorescence turns on response after the addition of Fe3+. In addition, the experimental results showed that the spirocyclic of L1 was opened by cooperation between L1 and Fe3+, and then the fluorescence emission after excitation of the mixture solution was detected with the change in solution colour. The complexation coefficient of L1 towards Fe3+ was 1:1. Furthermore, L1 for Fe3+ sensing had a remarkable low detection limit of 427 nM (UV) and 130 nM (fluorescence), which is far below the drinking water standards (0.3 mg/L) of China. Meanwhile, the in vivo imaging and cell viability assay experiments demonstrated that L1 could be used for sensing Fe3+ in vivo. [ABSTRACT FROM AUTHOR]

A colorimetric and fluorescence turn-off probe 10-(4-azido phenyl)-5,5-difluoro-5h-dipyrrolo[1,2-c:1',2'-f][1,3,2] diazaborinin-4-ium-5-uide, 1, for selective detection of H2S is reported. The probe displayed a robust decrease in fluorescence intensity with high sensitivity, specificity and least toxicity to detect exogenous H2S and also in live normal human oral fibroblast cells loaded with probe 1. The detection limit of probe 1 being 0.17 µm for H2S. A colorimetric and fluorescence turn-off BODIPY probe 1, for selective detection of exogenous H2S in live normal human oral fibroblast cells loaded with probe 1 and poisonous H2S gas formed under biodegradation in sewage waters and water tanks and corroded pipe lines. The detection limit of probe 1 being 0.17 μM [ABSTRACT FROM AUTHOR]

Nanoscale metal-organic frameworks (NMOFs) have been widely employed in biological diagnosis and treatment system. In this work, glutathione stabilized gold nanoclusters (GSH-AuNCs) were successfully encapsulated in NMOFs and the as-obtained nanocomposites (named as AuNCs@NMOFs) showed nearly 10 times enhancement in fluorescence intensity and longer fluorescence lifetime relative to GSH-AuNCs. In addition, the fluorescence intensity of AuNCs@NMOFs was quenched by highly reactive oxygen species (hROS) due to their strong oxidation ability. Based on the fact, the nanocomposites were used for the detection of hROS with a linear range from 80 nM to 1.0 μM toward hypochlorite (as the representative of hROS). The limit of detection (LOD) was about 30 nM, which was about 30 times lower than that of GSH-AuNCs (LOD = 0.96 μM). With the features of good biocompatibility, excellent luminescence and efficient cellular uptake, AuNCs@NMOFs were successfully applied in fluorescence imaging of hROS in living cells. Au nanoclusters@NMOF nanocomposites were prepared and further applied for hROS detection with high sensitivity in living cells. Image 1 • Au nanoclusters@NMOF composites were prepared as nanoprobe for hROS through a facile in-situ growth method. • The nanoprobe was developed to detect hROS with a fast response time and nearly 30 times sensitive than AuNCs. • The nanoprobe had been successfully applied in the imaging of exogenous and endogenous hROS in living cells. [ABSTRACT FROM AUTHOR]

A novel recyclable ratiometric fluorescent probe based on MOFs was designed and synthesized by a one-step approach, which was realized by assembling Al-MOFs in an aqueous solution containing rhodamine B (RhB) as a fluorescent reagent and Fe3O4 as a magnetically recyclable reagent. The obtained fluorescent probe (Fe3O4/RhB@Al-MOFs) has two emissions under excitation at 330 nm, in which the emission at 440 nm is attributed to the Al-MOFs and the emission at 610 nm presumably originates from the RhB dye. It was noted that the probe displays responses to Mg2+ ions with fluorescence enhancement at 440 nm, whereas the fluorescence at 610 nm would be a constant reference fluorescence signal. The existence of RhB significantly improves the detection accuracy and broadens the linear range. As a result, the selectivity of Fe3O4/RhB@Al-MOFs towards Mg2+ compared to other metal ions is excellent. When the Mg2+ ions (262.5 ppm) are added, the ratio of fluorescence intensity (I440/I610) is changed from 2.47 to 11.5. The Fe3O4/RhB@Al-MOFs show a rapid detection process (90 s), high fluorescence enhancement (up to 5-fold) and a low detection limit of Mg2+ ions (8 × 10−7 M). In particular, the magnetic Fe3O4 endows Fe3O4/RhB@Al-MOFs with a high magnetic responsiveness, thus, facilitating the separation procedures. As expected, it can be easily separated and recycled without a significant loss of recognition performance after being used many times, and thus, exhibits good reusability. Meanwhile, the cell cytotoxicity experiments suggest that Fe3O4/RhB@Al-MOFs is nearly non-toxic and in vitro cell imaging experiments demonstrate that the probe is capable of successfully enhancing fluorescence from the intracellular area in HL-7702 and A375 cellular systems. Hence, it has the potential for the detection of Mg2+ ions inside biosystems. [ABSTRACT FROM AUTHOR]

We report a triazole appended imidazopyridine based chemosensor (probe 1) for sequential detection of Cu2+ and CN− ions using fluorometry. Probe 1 is fluorescent in aqueous acetonitrile (H2O‐CH3CN, 1:1, v/v) when common metal ions are present, but the fluorescence is quenched when Cu2+ is present. The binding mechanism, quantitative determination and the mode of interaction of Cu2+ with probe 1 are explained using fluorescence spectroscopy, electrospray ionization mass spectrometry and Density Functional Theory (DFT) calculations. The observed detection limit for Cu2+ is found to be (18.17×10−6 M) and it is comparable with those reported for other Cu2+ chemosensors. Further, the 1–Cu2+ complex formation is found to be reversible, and this property has been successfully exploited for the quantitative determination of CN− ions in aqueous acetonitrile. Addition of CN– leads to a complete recovery of fluorescence from 1–Cu2+ complex, permitting the real time detection with the lower limit of detection of CN− being 33.57×10−6 M. The observed experimental results are supported by DFT calculations. A possible application of 1–Cu2+ in fluorescence imaging of Rhizoctonia solani mycelia cells, contaminated with CN− ions, is also represented. [ABSTRACT FROM AUTHOR]

A new coumarin-based probe 3-acetyl-7-diethylaminocoumarinthiosemicarbazone (DCT) is synthesized for Al3+ fluorescence detection in CH 3 CH 2 OH/H 2 O (6 : 4, v / v). The fluorescence intensity at 428 nm was enhanced about 15-fold with the fluorescence changed from colorless to blue. The binding constantof Al3+ with DCT is 5.04 × 106 M−1. The limit of detection (LOD) of Al3+ is calculated to be 82 nM. Furthermore, the binding details are determined by Job's plot and ESI - MS studies, which indicated that a stoichiometric ratio of 1 : 1 complex is formed between Al3+ and DCT. Cell imaging confirmed that DCT could useful for detecting Al3+ in HepG2 cells. • Probe DCT is highly selective and sensitive towards Al3+in aqueous solution phase with LOD is 82 nM,which could monitor intracellular Al3+ levels. • The mechanism indicated that a ratio of 1 : 1 complex is formed between Al3+ and DCT. [ABSTRACT FROM AUTHOR]

A facile synthesis procedure, whereby 9-Anthraldehyde (AA) is coupled to aminated rhodamine (AR) via a Schiff base-type reaction, is reported. The applicability and performance of the obtained material (AA-AR) as a sensing agent was studied towards 16 metal cations (i.e. Li+, Na+, Ag+, Ca2+, Ba2+, Co2+, Cs+, Cu2+, Mg2+, Hg2+, Mn2+, Pb2+, Ni2+, Sr2+, Zn2+, Al3+). Among the studied metals, an extraordinary selectivity was observed for Hg2+, and the observed selectivity was found not to be influenced by the presence of other cations and some common anions (i.e. Br−, Cl−, I−, HPO42−, H2PO4−, NO3−, NO2−, ClO4−, AcO−, HSO4−, SO42−, Cr2O7−, CO32−, OH− and HCO3−). The material, AA-AR, exhibited such a high selectivity and sensitivity towards Hg2+ that it could be detected even by naked eyes. The Hg2+-sensing property of AA-AR was found not to be limited to colorimetric detections so that a high fluorescent nature of the compound was also observed upon binding Hg2+ ion. The detection limit, which is correspondent to fluorescence emission intensity, was found as 0.87 μM. The underlying mechanism of sensing property was studied by using some spectroscopic techniques such as FT-IR, 1H-NMR, 13C-NMR, and UV-Vis. (Job-plot). In the final course of the experiments, the performance of AA-AR in cell-imaging was also studied, and even trace amounts of Hg2+ in living cells could be detected by the studied probe. Thus, the applicability of a new synthesis approach in producing a highly efficient new fluorescence sensor for the detection of Hg2+ ions is discussed in detail. [ABSTRACT FROM AUTHOR]

A novel Schiff base fluorescence probe (HL) was synthesized by the condensation of salicylaldehyde and an 8-aminoquinoline derivative. This probe acts as a "turn-on" dual selectivity fluorescence probe for Zn2+ and Al3+ ions, providing different colors and detection limits (DL) of 11.5 and 23.5 nM, respectively. Moreover, when Zn2+ and Al3+ co-exist, HL exhibits a preference for Al3+ by displacing Zn2+ from the HL-Zn2+ complex, realizing a dual-channel signal output for Al3+. The HL-Al3+ system could further discern F− by a "turn-off" fluorescence response with a DL of 86.0 nM. Furthermore, the probe HL was capable of monitoring intracellular Al3+, Zn2+ and F− in living PC12 cells in vitro through fluorescence imaging, which proved its value in potential in vivo applications. [ABSTRACT FROM AUTHOR]

• Small molecule fluorescence probe. • Highly selective for Ni (II) (≥160-fold). • Compatible with living cells. • Simple and low-cost detection. In this paper, we unveil a new highly selective and sensitive mito-tracker (NiP) for Ni2+ detection. NiP itself held very weak fluorescence and exhibited a high selectivity (≥160-fold) toward Ni2+ over other metal ions, with a limit of detection of 21.6 nmol. We demonstrate the practicality of NiP for the rapid determination of Ni2+ levels in mitochondria of living cells. This approach offers advantages by being fast, simple and low cost. [ABSTRACT FROM AUTHOR]

• A novel fluorescence strategy based on MPA-AgInZnS QDs for sensitive and effective detection of protamine and trypsin. • This assay we investigated was simple, cost-effective, convenient and does not need any complicated pretreatment. • We successfully applied the AgInZnS QDs to intracellular imaging and lysosomes localization. In this study, a fluorescence strategy based on MPA-AgInZnS quantum dots (AIZS QDs) for the sensitive, effective detection of protamine and trypsin was developed. Protamine as a cationic peptide exhibited electrostatic interactions with AIZS QDs, leading to the aggregation of QDs and subsequent enhancement of the fluorescence intensity. The added trypsin catalyzed the hydrolysis of protamine and led to less formation of AIZS QDs/protamine complex, thereby decreasing the fluorescence intensity. Thus, a method for direct determination of protamine and indirect measurement of trypsin using protamine as a tool was developed. The protamine and trypsin concentrations were determined by the detection of the change in fluorescence intensity. Under the optimized conditions, the fluorescence intensity exhibited a good linear response to the protamine concentration, with a limit of detection (LOD) of 0.13 μg mL−1, and trypsin exhibited a linear relationship, with an LOD of 0.04 μg mL−1. The probe exhibited good biocompatibility and low cytotoxicity according to the MTT assay. Moreover, the application of this probe for intracellular imaging and lysosome localization demonstrates potential development in the biomedical and clinical fields. [ABSTRACT FROM AUTHOR]

Fluorescent carbon quantum dots (CQDs) can be prepared by sonochemistry with low cost and high efficiency. However, ultrasonic synthesis of CQDs with responsive fluorescence towards environmental stimuli remains a big challenge. Herein, we report a simple one-step method to fabricate versatile nitrogen-doped CQDs (NCQDs) by ultrasonic treatment of dopamine in dimethylformamide for 8 h. The obtained NCQDs simultaneously possess superior water dispersibility and stability, bright and stable fluorescence against variations of pH and ionic strength, low cytotoxicity and high photostability. Moreover, the fluorescence of NCQDs showed sensitive quenching phenomenon towards Fe2+ ions both in water and in the interior of cancer cells. The emission intensity of NCQDs exhibited good linear relationship (R 2 = 0.9987) with the concentration of Fe2+ ions in the range of 0–50 μM. The limit of detection can reach as high as 38 nM. Meanwhile, the NCQDs also exhibited temperature-dependent fluorescence with favorable linear relationship (R 2 = 0.9965) in the range of 283–358 K, and thus can server as a nanothermometer to sense temperature both in water and in cells. Unlabelled Image • Ultrasonic synthesis of versatile fluorescent NCQDs from dopamine was reported. • NCQDs showed high water dispersibility, stable fluorescence, and low cytotoxicity. • The fluorescence of NCQDs exhibited sensitive quenching behavior towards Fe2+ ions. • N-CQDs also presented temperature-dependent fluorescence behavior. [ABSTRACT FROM AUTHOR]

• A novel fluorescence sensor (TCS) for Pd2+ was designed and synthesized. • TCS exhibited selective sensing abilities for Pd2+ among various metallic ions. • The detection limit for Pd2+ was as low as 4.32 × 10−8 M. • The sensing mechanism of 1:1 stoichiometry ratio was confirmed. • TCS displayed good bioimaging performance on Pd2+ detection in living system. Although some Pd2+ sensors were presented, the in-situ and real-time examination of Pd2+ based on fluorescent sensor is still a challenging task. In this work, a novel thiourea-cyanostilbene derivative (TCS) was designed and synthesized as the effective fluorescent sensor on in-situ and real-time sensing Pd2+ in aqueous media. TCS possessed good AIE fluorescence in THF/H 2 O solution. The fluorescence was selectively quenched by Pd2+ among all kinds of metallic ions. The sensing mechanism of 1:1 stoichiometry ratio for TCS with Pd2+was confirmed by Job's plot, 1H NMR and MS spectra. The detection limit was as low as 4.32 × 10−8 M. TCS exhibited the good sensing application for Pd2+ in tested paper and simulated samples with low errors. TCS had the excellent fluorescence imaging performance in living cells with the fluorescence imaging response on Pd2+. This research not only reported an effective fluorescence sensor for Pd2+, but also suggested the good application prospect on in-situ and real-time sensing Pd2+ in complicated environment. [ABSTRACT FROM AUTHOR]

• A novel NIR colorimetric-fluorescence probe was prepared for detection of hydrogen sulfide. • The probe showed rapid, specific and sensitive detection of hydrogen sulfide with a large Stokes shift. • The probe was capable of imaging hydrogen sulfide in living cells and mice. We presented here a novel near-infrared fluorescent probe based on 2-(2′-hydroxyphenyl)benzothiazole -dicyanoisophorone as fluorophore and 2,4-dinitrobenzenesulfonyl moiety as detection functionalized group for the discrimination of hydrogen sulfide (H 2 S). Probe L exhibited good specificity and sensitivity "turn on" response at 720 nm with a large Stokes shift (155 nm), rapid response (< 60 s) and low detection limit (3.15 × 10−7 M), which also could be identified by the naked eyes. Moreover, probe L was successfully used to image exogenous/endogenous H 2 S in cells and mice, which demonstrated its potential applications in living systems. A novel fluorescein based on 2-(benzo[ d ]thiazol-2-yl)phenol-dicyanoisophorone probe was constructed for the discrimination of hydrogen sulfide. The probe was applied for the rapid, sensitive, large Stokes shift, colorimetric and large near-infrared fluorometric determination of H 2 S, based on the displacement approach. The low cytotoxicity and excellent imaging performance was successfully applied for mitochondrial localization in living cells and endogenous and exogenous H 2 S detection in vivo. [Display omitted] [ABSTRACT FROM AUTHOR]

Hypochlorous/Hypochlorite(HClO/ClO−) plays an important biochemistry roles in normal operation of the life system. Herein, a fluorescent probe 7‐chloro‐3‐((E)‐3‐(4‐(dimethylamino)phenyl)‐ acryloyl)‐2H‐chromen‐2‐one (CCO) was rationally designed and synthesized via aldehyde ketone condensation reaction to detect ClO− in Tris‐HCl (pH=7.2, 60% DMF) solution. Probe CCO was cleaved conceivably in the coumarin lactone ring by an oxidation reaction with ClO− and emitted intensive bright yellow fluorescence. The sensing mechanism was further confirmed by ESI‐MS and DFT calculation. The fluorescence emission of probe CCO triggered by ClO− was obviously enhanced within 20 s. The limit of detection of probe CCO was calculated as low as 2.6 nM. Furthermore, probe CCO can be given as an effective and outstanding fluorescent exogenous ClO− probe in living HEK293T cells for microscopic cell imaging. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H 2 S) is a kind of gaseous signal molecule in many physiological processes. In order to detect H 2 S, a novel "turn on" fluorescent probe 6,12-dihydroxyperylene-1,7-dione (DPD) was designed and synthesized. The probe DPD is fluorescence silence, while the addition of H 2 S induces an obvious green fluorescence with an obvious color change from dark blue to yellow-green. The probe shows excellent selectivity, fast response (2.5 min) and linear curve (0–90 μM) in wide effective pH range (4–10). Competition experiments are also revealed in corresponding studies and the detection limit is 3.6 μM. The response mechanism is proved to be the reduction of the probe by H 2 S, which is confirmed by 1H NMR. Furthermore, through the fluorescence turn-on signal toward H 2 S in Hela cells, probe DPD was successfully applied to monitor H 2 S in living Hela cells. Unlabelled Image • A "turn-on" probe DPD for hydrogen sulfide was developed. • DPD shows highly selective and sensitive response to hydrogen sulfide. • DPD shows rapid response and high sensitivity toward hydrogen sulfide. • The response mechanism of the probe DPD with H 2 S was confirmed to be reduction of carbonyl groups to hydroxyl groups. • DPD can monitor the exogenous cysteine in solution and living cells. [ABSTRACT FROM AUTHOR]

Abstract A red emissive fluorescent probe 1,7-dimethyl-3,5-bis(4-methoxyphenyl-vinyl)-8-(10-n-butyl-10H-phenothiazine-3-yl)BODIPY 1,7-dimethyl-3,5-bis(4-methoxyphenyl-vinyl)-8-(10- n -butyl-10 H -phenothiazine-3-yl)BODIPY (avyl-BODIPY-PTZ) with a special orthogonal donor-acceptor structure was designed and synthesized for rapid, sensitive, and selective discrimination of ClO−, over other reactive oxygen species and anions. The probe displays a linear ratiometric absorption (A 578 /A 640) and fluorescence (F 599 /F 660) response toward ClO− with a fast response velocity (~10 s). The limit of detection (LOD) for ClO− was obtained as 22.6 nM from the fluorescence titration experiment. The fluorescence enhancement of the probe can be observed from the 32-fold enhancement in ratiometric value (F 599 /F 660) and the increasement of quantum yield from 0.01 at 660 nm to 0.28 at 599 nm. The oxidation of S atom in phenothiazine by ClO− to form the sulfoxide-type structure was proposed as the recognizing mechanism according to the Mass spectral analysis. The ratiometric enhancement of fluorescence was rationalized by the theoretical calculations. The orthogonal donor-acceptor structure according to optimized calculation and solvent effects of avyl-BODIPY-PTZ illustrated that the ClO− oxidation induced conversion from the nonradiative TICT process to the radiative LE process and caused the fluorescence ratiometric enhancement. The probe with low cytotoxity can successfully permeate into living cells and the cell images can be achieved in single channel. Moreover, after addition of ClO−, another bright red emission channel of the probe switched on and the probe displayed two-channel emission in living cells. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

Abstract An electron pushing group has been introduced to a Schiff-base compound, 2-((2-(quinolin-2-yl)hydrazono)methyl)phenol (HQP) to get another Schiff-base molecule, namely, 4-methyl-2-((2-(quinolin-2-yl)hydrazono)methyl)phenol (HMQP), to modulate the Zn2+ sensing properties of the probe. HQP and HMQP have been synthesized by Schiff-base condensation between 2-hydrazinylquinoline and the respective aldehyde in 1:1 ratio and characterized by standard methods. Both the compounds show their Zn2+ sensing ability but to different extents. The fluorescence intensity of HQP at ~490 nm (λ ex = 410 nm) increases by about 4.5 folds in the presence of one equivalent of Zn2+ ion. However, the fluorescence intensity is enhanced by around 30 folds in the presence of one equivalent of Zn2+ in case of HMQP. The fluorescence peak of HMQP at 502 nm (λ ex = 420 nm) is shifted to 515 nm in the presence of Zn2+ whereas same type of shifting for HQP is found to be negligible. Some theoretical calculations have been performed to look into the spectral transitions of HMQP. Fluorescence intensity enhancement is explained by PET mechanism. Limit of detection (LOD) value for HMQP has been determined to be 220.6 nM, showing its good sensitivity towards zinc. The color change of HMQP under visible light is not conclusive in the presence of different metal ions, but only Zn2+ can induce green coloration to HMQP solution under UV light, thus indicating the possibility of naked eye detection by the analyte. HMQP with one equivalent of Zn2+ displays high fluorescence intensity in the pH range of 7.0–9.0 indicating its suitability towards biological applications. The probe has been utilized to live cell imaging studies using C6 cells. Graphical abstract Fluorescence intensity of 4-methyl-2-((2-(quinolin-2-yl)hydrazono)methyl)phenol increases hugely in the presence of Zn2+ than that of 2-((2-(quinolin-2-yl)hydrazono)methyl)phenol, which differs by a methyl group. fx1 [ABSTRACT FROM AUTHOR]

For highly sensitive and selective detection of ClO− over other reactive oxygen species (ROS) and anions, a fluorescent probe MN-BODIPY by introducing a morpholine group into the 8-position of BODIPY which could be used for targeting lysosome and improving water solubility was designed and synthesized. As a result of the C=N isomerization mechanism at 2-position of BODIPY, the probe alone generated extremely weak fluorescence. However, in the presence of ClO−, the probe exhibited a dramatic enhancement of fluorescence intensity by a 29-fold increase at 530 nm accompanying with quantum yield changing from 0.03 to 0.25. Accordingly, the probe displayed fast response for ClO− within 60 s. The limit of detection (LOD) for ClO− was calculated as 16.5 nM from the titration experiments, which is lower than most previously reported ClO−-selective probes. Moreover, MN-BODIPY had been successfully employed for monitoring exogenous and endogenous hypochlorous in MCF-7 cells with satisfying results, perhaps it was feasible for detecting abnormal contents of hypochlorous in a biological system and accomplished the goal of maintaining normal human activities. At last, the fluorescence imaging showed that MN-BODIPY was capable of localizing lysosomes in living cells. Image 1 • MN-BODIPY displayed fast response towards ClO− within 60 s. • MN-BODIPY recognized ClO− with lower limit of detection of 16.5 nM. • MN-BODIPY was applied for intracelluar ClO− bioimaging. • MN-BODIPY could target lysosome. [ABSTRACT FROM AUTHOR]

Abstract In this work, we have designed and synthesized a dinitrobenzene-sulfonate tetrahydro[5]helicene (H-DNP) as an effective fluorescent probe for detection of hydrogen sulfide (H 2 S). Upon the addition of H 2 S, a significant fluorescence enhancement (75-fold) at 495 nm can be observed with a distinct color change from colorless to yellow. Additionally, H-DNP shows low background spectroscopic signal, large Stokes Shift up to ~140 nm, good sensitivity, rapid response time less than 2 min, low detection limit (48 nM) and high selectivity toward common bio-thiols (Cysteine, Homocysteine and Glutathione). Compared with the previous dinitrophenoxy tetrahydro[5]helicene, this probe has shorter response time and lower detection limit. Most importantly, this probe H-DNP has low toxicity to cells and excellent cell permeability, which can be applied to visualize H 2 S in living cells. Graphical abstract Unlabelled Image Highlights • A tetrahydro[5]helicene based fluorescence probe displayed a rapid, sensitive and selective in response to H 2 S. • The probe has very low detection limit and fast response time. • The response mechanism is confirmed to be thiolysis reaction induced by H 2 S. • The detection of intracellular H 2 S was successfully demonstrated in living cells. [ABSTRACT FROM AUTHOR]

A new "turn-on" fluorescent probe Py based on rhodamine and piperonaldehyde was designed and synthesized for detecting Fe3+ in cells. The free probe Py was non-fluorescent. While only upon addition of Fe3+, the significant increase of the fluorescence and color were observed which could be visible directly by "naked-eye". The probe Py shows high selectivity and sensitivity for Fe3+ over other common metal ions in EtOH-H2O (3/2, v/v) mixed solution. The association constant and the detection limit were calculated to be 4.81 × 104 M−1 and 1.18 × 10−8 mol/L respectively. The introduction of piperonaldehyde unit could increase probe rigidity which could enhance its optical properties. Meanwhile, the binding mode between Py and Fe3+ was found to be a 1:1 complex formation. The density functional theory (DFT) calculations were performed which would further confirm the recognition mechanism between probe Py and Fe3+. In addition, the probe has been proved to be reversible for detecting Fe3+. Moreover, the probe Py was used to detect Fe3+ in cells successfully. [ABSTRACT FROM AUTHOR]

A series of naphthalene carbohydrazone based fluorescent chemosensors L 1 -L 4 were developed for the detection of Zn 2+ by significant fluorescence enhancement. The binding ratio of the L 1 -Zn 2+ complex was determined by a Job’s plot to be 1:1 and confirmed by ESI–MS studies. The corresponding of the L 1 -Zn 2+ ensemble was elucidated through X-ray crystallography along with spectroscopic studies. Furthermore, the L X -Zn 2+ (X   =   1–2) complexes can specifically detect pyrophosphate (PP i ) in HEPES buffer solution through fluorescence quenching. The detection limit of L X -Zn 2+ (X   =   1–2) for PP i sensing were calculated to be as low as 2.54 ppb and 0.94 ppb, respectively. In addition, due to their good cell membrane permeability and low cytotoxicity, L 1 -L 4 have been applied to sequentially detect Zn 2+ and PP i in living cells. More importantly, the electronic effect of substitute groups on fluorescence signaling have been studied by substituent properties ranging from electron-donating to electron-withdrawing, which sets up a promising strategy for the rational design of fluorescent sensors. [ABSTRACT FROM AUTHOR]

[Display omitted] • The near-infrared (NIR) turn-on fluorescence probe (aza-BDP-Pro) based on aza-BODIPY derivative was prepared for detecting Au3+ ions. • Aza-BDP-Pro probe can detect Au3+ with a low detection limit in aqueous solution. • The probe showed a remarkable fluorogenic change under UV light. • Aza-BDP-Pro was acceptable applied as an intracellular Au3+-tracking agent in living human cells. A new near-infrared (NIR) fluorescent probe for the determination of Au3+ ions was synthesized by introducing boron dipyrromethene moiety as a fluorophore and attaching it with propyne groups as a Au3+-specific recognition unit. The photophysical properties revealed that the fluorescent emission of the sensor was observed in the NIR region with a wavelength of 713 nm. Furthermore, the sensor exhibited excellent sensitivity to Au3+ ions with fluorescent enhancement behavior in aqueous media and naked-eye observation through a colorimetric change from green to yellow. The detection limit of aza-BDP-Pro was found to be 0.64 µM (0.126 ppm). The probe was successfully utilized for selectively detecting Au3+ ions against other 18 interfering metal ions and tracking Au3+ ions in vivo for imaging application. [ABSTRACT FROM AUTHOR]

The abnormal expression of cytochrome P450 2J2 (CYP2J2) is closely related to the proliferation of human cancer cells. In this study, a red-emitting probe with an aggregation-induced emission (AIE) effect for the quantification of CYP2J2 was developed by modifying the typical AIE fluorescent group tetraphenylethylene (TPE) through two-step synthesis. Upon addition of CYP2J2, the probe underwent O-demethylation and spontaneously 1,6-elimination reactions of p-hydroxybenzyl that allowed it to alter its photophysical properties, thus realizing light-up detection of CYP2J2 with extremely large Stokes shift (236 nm), excellent sensitivity and selectivity, low detection limit (1.09 nM). Moreover, this new AIE-active probe with good biocompatibility was admirably employed to tracking endogenous CYP2J2 in living cells. • An AIE-based fluorescent probe (TPE-Bn) was designed to detect CYP2J2. • This probe showed significant Stokes shift (236 nm), good photostability, excellent sensitivity and selectivity, and low cytotoxicity. • This probe can be used to visualize endogenous CYP2J2 in living cells and tissues. [ABSTRACT FROM AUTHOR]