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[Display omitted] • A Zn2+ selective turn-on optical sensor (DIH) with ESIPT process was reported. • DIH showed high selectivity and sensitivity Zn2+ over other metal ions tested. • The detection mechanism was elucidated by ESI–MS, NMR and DFT calculations. • The sensor is suitable for imaging Zn2+ in living cells. Zinc ions (Zn2+) play a significant role in our daily lives and production, which is related to human health and environment protection. Therefore, it is crucial in this field to develop sensors with improved analyte selectivity and sensitivity. We prepared a fluorescent sensor, DIH, through the reaction of 5-(tert -butyl)-2-hydroxyisophthalaldehyde with isonicotinohydrazide. DIH, in free form, can undergo excited state intramolecular proton transfer (ESIPT) process upon excitation. Among a wide range of metal ions tested, only Zn2+ inhibited this ESIPT process, resulting in an increase in fluorescence intensity (13.3-fold) with chelation enhancement fluorescence process (CHEF). The complex (DIH/Zn2+) stoichiometry was determined to be 1:1 and the binding constant of the complex was estimated as 3.18 × 107 M−1. DIH could also be applied to detect zinc ions down to a low concentration level of 11.2 nanomolar with fluorescence spectroscopy. Moreover, the cytotoxicity evaluation of DIH against human colon adenocarcinoma cells lines demonstrated that the sensor was nontoxic and could be used successfully in cellular imaging. [ABSTRACT FROM AUTHOR]

Abstract Hydrazino-carbothioamide, 1 , serves as a turn-on fluorescent chemosensor to Zn2+ and the mixture shows green emission (λ em 492) in presence of large number of ions with impressive limit of detection (LOD), 0.59 nM. Intense fluorescence of Zn-complex is selectively turn-off upon adding H 2 PO 4 − only to the limit of detection, 26 μM, while other anions remain silent. The sensing mechanism of 1 is established by suppressing the ESIPT of 1 and complexation with Zn2+ (CHEF) is supported by Job's plot, 1H NMR, and HR-MS data. Turn-on-off sequential detection of Zn2+ and H 2 PO 4 − also have successfully been employed for the engineering of INHIBIT molecular logic gate. The sensor is non-toxic and has been used in identifying Zn2+ in the intracellular region of African green monkey kidney cells (Vero cells). Graphical Abstract Very low detection limit (0.59 nM) is shown by green emission (492 nm) of hydrazino-carbothioamide probe on binding selectively with Zn2+ at pH, 7.2 which is specifically quenched by H 2 PO 4 − with LOD, 26 μM. This probe uses detection of Zn2+ in Vero cells and INHIBIT logic gate is constituted. Unlabelled Image Highlights • Hydrazino-carbothioamide sensor shows green emission with Zn2+. • Highly selective turn-on Zn2+ sensor shows LOD 0.59 nM. • Emission of the complex is quenched specifically upon addition of H 2 PO 4 − and LOD is 26 μM. • The sensor is non-toxic and identifies Zn2+ in the intracellular region of Vero cells. • Emission change at 492 nm with Zn2+ and H 2 PO 4 − can be described to INHIBIT logic gate. [ABSTRACT FROM AUTHOR]

The development of sensitive chromogenic chemosensors for sensing Cu 2+ has been receiving much attention in recent years because of their potential application in clinical biochemistry and the environment studies. Numerous chemosensors have been developed for selective recognition of different species on the basis of host–guest interactions such as hydrogen-bonding, electrostatic force, metal–ligand coordination, hydrophobic and van der Waals force of interactions. The simple and rapid sensing of Cu 2+ ions in biological and environmental systems is desirable and the development of selective and sensitive imaging tools capable of monitoring Cu 2+ ions rapidly has attracted considerable attention. Fluorescent chemosensors have served as useful tool for detecting metal ions owing to their intrinsic sensitivity, selectivity and capacity for rapid, real-time monitoring. Small-molecule fluorescent probes can make use of selective, bio-orthogonal chemistries to report on specific analytes in cells and in more complex biological specimens. This review presents a survey of strategies for using small-molecule fluorescent probes to detect Cu 2+ ions which cover UV to NIR regions such as anthracene, pyrene, quinoline, quinazoline, dansyl, naphthalimide, rhodamine, fluorescein, BODIPY and cyanine dyes. [ABSTRACT FROM AUTHOR]

Copper(II), Cu 2+ , ion plays not only a fundamental role to sustain important physiological processes in living organisms, but also an important environmental pollutant. A large number of chemosensors that employ the chromogenic, fluorogenic or electrochemical properties of molecules have been reported for selective sensing of copper ions with absorbance and emission in the visible region. Nevertheless, most of these chemosensors for Cu 2+ ions have some limitations including low water-solubility, tedious sample treatment, multistep synthetic routes, or unstable detection signal. Therefore, the challenge in the development of light-up chemosensors which are cost-effective, rapid, facile, biocompatible and applicable to the environmental and biological milieus is still a topical issue. In the context of optical sensing of Cu 2+ ion, the unique features offered by transition metal complexes over organic fluorophores have made them a suitable candidate to monitor Cu 2+ ions in biological systems. Encouraged by the importance of Cu 2+ ions, we herein summarize the recent development of transition metal complexes, particularly those of d 6 or d 10 complexes based on rhenium(I), ruthenium(II), iridium(III), zinc(II) and gold(I) complexes, for optical and electrochemical sensing or biosensing applications of Cu 2+ ion. [ABSTRACT FROM AUTHOR]

Although a variety of fluorescence based chemosensors have been utilized for selective detection of Zn 2+ , pyridoxal containing simple Schiff bases still remained less explored. Here, we combine pyridoxal hydrochloride and 1,2-diaminocyclohexane to generate a new sensor molecule, H 4 PydChda [5-Hydroxymethyl-4-({2-[5-hydroxymethyl-2-methylpyridin-3-hydroxy-4-ylethylene)-amino]-cyclohexylimino}-methyl-2-methylpyridin-3-ol]. Chemosensor H 4 PydChda exhibits selective turn-on type response in presence of Zn 2+ in ethanol-water mixture at physiological pH. Appreciable fluorescence enhancement occurs upon addition of Zn 2+ to H 4 PydChda as a result of inhibited C N isomerisation and excited state intramolecular proton transfer (ESIPT) leading to efficient chelation enhanced fluorescence (CHEF). The relevant properties, including reversibility, life time measurements and detection limit have been determined for the sensor system. The experimental and theoretical supports in terms of 1 H and 13 C NMR spectroscopy and DFT/TDDFT study are provided to establish the binding mode of H 4 PydChda to Zn 2+ . H 4 PydChda was employed as a sensor for detection of Zn 2+ in Human gastric adenocarcinoma (AGS) cells. Moreover, the resulting probe-Zn 2 + complex shows convincing phosphatase activity (k cat = 21.59 s −1 ), opening a promising avenue for further research. [ABSTRACT FROM AUTHOR]

The chemosensor 2,3-bis((E)-((2-hydroxynaphthalen-1-yl)methylene)amino)maleonitrile ( 1 ) has been synthesized using 2-hydroxy-1-napthaldehyde and 2,3-diaminomaleonitrile and characterized. Sensor 1 exhibits selective binding with CN − in dimethyl sulfoxide (DMSO)/H 2 O (7:3 v/v) and DMSO/aqueous Tris (Tris(hydroxymethyl)aminomethane) buffer (7:3 v/v, 10 mM, pH 7.2) media with significant changes in its UV–visible and fluorescence spectra. Titration of 1 -Zn(II) complex with CN − ion in DMSO/aqueous Tris buffer (7:3 v/v, 10 mM, pH 7.2) regenerates the free sensor 1 , as supported by UV–visible spectra. 1 H NMR titration of 1 with CN ‒ in (CD 3 ) 2 SO confirms the hydrogen-bonding interaction between the two OH groups of the former and the latter in bidentate manner. Sensor 1 impregnated on silica gel thin layer chromatography (TLC) strip followed by dipping in anion solutions in DMSO/H 2 O (7:3 v/v) generates yellow to red spectacular colour change with CN − ion selectively which can be exploited as potential tool for ready-made detection of toxic CN − ion in environmental and analytical chemistry. Similar visual change in colour for 1 is observed selectively with CN − also when both of them are taken in DMSO/H 2 O (7:3 v/v) solution. Sensor 1 is used as an imaging reagent for detection of the cellular uptake of CN − ion in Baby Hamster Kidney (BHK-21) cells. [ABSTRACT FROM AUTHOR]

A novel fluorescein-rhodamine dyad probe has been synthesized and its chemosensory applications are explored. Anion and cation specific responses of the probe permit ratiometric detection of Hg 2+ and fluoride ions, individually and collectively, with different fluorescence outputs. The presence of other commonly coexistent ions does not affect the Hg 2+ and fluoride ion detection ability of the probe. The probe is highly sensitive to Hg 2+ and fluoride ions and it can detect Hg 2+ and fluoride ions even at ppb level concentrations. The probe is non-toxic under the experimental conditions, cell permeable and useful for the imaging of intracellular Hg 2+ and fluoride ions. [ABSTRACT FROM AUTHOR]

• A phenolphthalein-aminophenol (PFAP)-based chemosensor for Al3+ was synthesized. • PFAP showed a LOD of 1.5 µM and a fast response time of 10 s. • PFAP was used to detect Al3+ in the intracellular region of the A549 cancer cells. Monitoring of excess Al3+ and its selective detection in biological and environmental samples are important tasks for researcher due to its harmful effects. Herein, we present a phenolphthalein-aminophenol derived sensor (PFAP) for the selective fluorescent response of Al3+ in an "OFF-ON" mode over a pool of analytes including eighteen cations with striking greenish emission. It has a prominent limit of detection (LOD) value (1.5 µM), fast response time (10 s) for Al3+ detection. The complexation properties of PFAP with Al3+ ions were clarified by UV–vis, 1H & 13C NMR, HRMS, and FTIR spectroscopic experiments. The recognition mechanism of PFAP for Al3+working with chelation enhanced fluorescence (CHEF) and is verified with two model compounds PF and PFAN in the light of UV–vis, PL, TRPL, and NMR experiment. To check its applicability, easily prepared test paper and TLC strip of PFAP was produced for rapid and selective onsite detection of Al3+ ions. Bio-imaging application of PFAP in human lung cancer cell lines A549 demonstrated excellent results with negligible cytotoxicity and as an excellent marker to detect traces of Al3+ ion in a time-dependent as well as concentration-dependent manner. Actual sample analysis for Al3+ with the probe PFAP produces fruitful result. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: A malonohydrazide derivative bearing an imine and phenolic group was synthesized and had a high affinity and selectivity towards Zn2+. The recognition properties of receptor 1 were evaluated using absorbance and fluorescence spectroscopy. The 1:1 stoichiometry of 1.Zn2+ was confirmed from job׳s plot, mass spectra and density functional theory (DFT). The detection of Zn2+ in intracellular environment of HeLa cell through confocal microscopy was successfully applied for live cell imaging. [Copyright &y& Elsevier]

Abstract: The size of the chelating ligand and nature of coordinating entities of the chelating moiety have been exploited to synthesize four rhodamine based chemosensors for selective recognition of metal ions. A triazole appended colorless chemosensor turns to pink upon complex formation only with Cu2+ ions even in the presence of other competing metal ions at physiological pH, and enables naked-eye detection and imaging of live fibroblast cells exposed to Cu2+ ions. [Copyright &y& Elsevier]

A bisphenol based fluorescence "turn-on" chemosensor 4,4′-(propane-2,2-diyl)bis(2-((E)-(2-(benzo[d]thiazol-2-yl)hydrazineyldene)methyl)phenol) (BHMP) has been synthesized and its sensing behavior was tested towards various ionic species. The chemo-sensing behavior of BHMP has been established through absorption, fluorescence, NMR, and mass spectroscopic techniques. The probe BHMP selectively detects zinc ions over other metal ions and the resulting BHMP + Zn2+ ensemble serves as a secondary probe for the detection of pyrophosphate (PPi) anion specifically over other anions. The spectroscopic studies reveal the fluorescence enhancement of BHMP in association with Zn2+ ions was quenched in the presence of pyrophosphate (PPi) anions. A probable mechanism of this selective sensing behavior was described on the basis of "OFF-ON-OFF" strategy for detection of both cations and anions. Moreover, the biological applicability of the chemosensor BHMP was examined via cell imaging studies. A bisphenol based fluorescence "turn-on" chemosensor (BHMP) has been synthesized and its sensing behavior was tested towards various ionic species. The probe BHMP selectively detects zinc ions over other metal ions and the resulting Zn2+-BHMP ensemble serves as a secondary probe for the detection of PPi anion. The biological applicability of the chemosensor BHMP was examined via cell imaging studies. Unlabelled Image • The probe BHMP selectively detects zinc ions and the resulting Zn2+- BHMP ensemble is applied for the detection of PPi ions. • The probe detects Zn2+ and PPi ions with low detection limit of 0.28 and 0.87 nM respectively. • The probe was successfully applied to detect Zn2+ and PPi ions in live cells. [ABSTRACT FROM AUTHOR]