Highly selective ratiometric fluorescent Zn2+ chemosensor based on diarylethene derivative with bi‐8‐carboxamidoquinoline unit

An asymmetrical diarylethene (1O) with a bi‐8‐carboxamidoquinoline unit was synthesized. Its photochromic and fluorescence performances on stimulation with both light and metal ions showed that the diarylethene could serve as a highly selective ratiometric fluorescent chemosensor to detect Zn²⁺ ions based on internal charge transfer and chelation‐enhanced fluorescence processes. The diarylethene could selectively discriminate Zn²⁺ from Cd²⁺ in acetonitrile. Furthermore, Job's plots based on fluorescence titration and electrospray ionization mass spectrometry analysis showed 1 : 1 binding stoichiometry between 1O and Zn²⁺. The binding constant of 1O with Zn²⁺, estimated using the Benesi–Hildebrand method, and the limit of detection were 3.37 × 10⁵ M^–1 and 4.6 × 10^–8 mol/L, respectively. Additionally, the light and metal‐responsive fluorescence behavior of 1O was used successfully to construct a molecular logic circuit with four inputs and one output. Copyright © 2016 John Wiley & Sons, Ltd.     

Ratiometric fluorescent detection of Cu2+ based on dual‐emission ZIF‐8@rhodamine‐B nanocomposites

Zeolitic imidazolate framework‐8 (ZIF‐8) loading rhodamine‐B (ZIF‐8@rhodamine‐B) nanocomposites was proposed and used as ratiometric fluorescent sensor to detect copper(II) ion (Cu²⁺). Scanning electron microscopy, Fourier transform infrared spectroscopy, X‐ray powder diffraction, nitrogen adsorption/desorption isotherms and fluorescence emission spectroscopy were employed to characterize the ZIF‐8@rhodamine‐B nanocomposites. The results showed the rhodamine‐B was successfully assembled on ZIF‐8 based on the π‐π interaction and the hydrogen bond between the nitrogen atom of ZIF‐8 and –COOH of rhodamine‐B. The as‐obtained ZIF‐8@rhodamine‐B nanocomposites were octahedron with size about 150–200 nm, had good water dispersion, and exhibited the characteristic fluorescence emission of ZIF‐8 at 335 nm and rhodamine‐B at 575 nm. The Cu²⁺ could quench fluorescence of ZIF‐8 rather than rhodamine‐B. The ZIF‐8 not only acted as the template to assemble rhodamine‐B, but also was employed as the signal fluorescence together with the fluorescence of rhodamine‐B as the reference to construct a novel ratiometric fluorescent sensor to detect Cu²⁺. The resulted ZIF‐8@rhodamine‐B nanocomposite fluorescence probe showed good linear range (68.4 nM to 125 μM) with a low detection limit (22.8 nM) for Cu²⁺ combined with good sensitivity and selectivity. The work also provides a better way to design ratiometric fluorescent sensors from ZIF‐8 and other fluorescent molecules.     

Multifunctional peptide‐based fluorescent chemosensor for detection of Hg2+, Cu2+ and S2− ions

A novel multifunctional fluorescent peptide sensor based on pentapeptide dansyl‐Gly‐His‐Gly‐Gly‐Trp‐COOH (D‐P5) was designed and synthesized efficiently using Fmoc solid‐phase peptide synthesis (SPPS). This fluorescent peptide sensor shows selective and sensitive responses to Hg²⁺ and Cu²⁺ among 17 metal ions and six anions studied in N‐2‐hydroxyethylpiperazine‐N‐2‐ethane sulfonic acid (HEPES) buffer solution. The peptide probe differentiates Hg²⁺ and Cu²⁺ ions by a ‘turn‐on’ response to Hg²⁺ and a ‘turn‐off’ response to Cu²⁺. Upon addition of Hg²⁺ or Cu²⁺ ions, the sensor displayed an apparent color change that was visible under an ultraviolet lamp to the naked eye. The limits of detection (LOD) of DP‐5 were 25.0 nM for Hg²⁺ and 85.0 nM for Cu²⁺; the detection limits for Cu²⁺ were much lower than the drinking water maximum contaminant levels set out by the United States Environmental Protection Agency (USEPA). It is noteworthy that both D‐P5‐Hg and D‐P5‐Cu systems were also used to detect S^2? successfully based on the formation of ternary complexes. The LODs of D‐P5‐Hg and D‐P5‐Cu systems for S^2? were 217.0 nM and 380.0 nM, respectively. Furthermore, the binding stoichiometry, binding affinity and pH sensitivity of the probe for Hg²⁺ and Cu²⁺ were investigated. This study gives new possibilities for using a short fluorescent peptide sensor for multifunctional detection, especially for anions.     

Rhodol‐based far‐red fluorescent probe for the detection of cysteine and homocysteine over glutathione

The simultaneous discrimination of cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) is of great importance due to their roles in biology and close link to many diseases, especially via the development of a far‐red fluorescent probe that could be used for rapid, selective, and sensitive detection of all three. Herein, we report the characterization of a far‐red fluorescent probe with turn‐on fluorescence properties and visible color changes that could be used for the detection of cysteine and homocysteine over glutathione. In this study we found that the sensor could discriminate cysteine and homocysteine over glutathione within 20 min. Function of this probe was based on the conjugate addition–cyclization reaction and showed a low detection limit to cysteine and homocysteine. Upon the addition of cysteine and homocysteine, the absorption band at 592 nm rose gradually and fluorescence was detected at 645 nm. The color changed from colorless to blue and fluorescence changed from absent to strong red fluorescence, which could be differentiated by the naked eye. All these unique features make this probe particularly potentially favorable for use in cysteine/homocysteine sensing and bioimaging applications. Copyright © 2016 John Wiley & Sons, Ltd.     

Glutathione‐stabilized Cu nanocluster‐based fluorescent probe for sensitive and selective detection of Hg2+ in water

In this paper, an innovative and facile one‐pot method for synthesizing water‐soluble and stable fluorescent Cu nanoclusters (CuNCs), in which glutathione (GSH) served as protecting ligand and ascorbic acid (AA) as reducing agent was reported. The resultant CuNCs emitted blue‐green fluorescence at 440 nm, with a quantum yield (QD) of about 3.08%. In addition, the prepared CuNCs exhibited excellent properties such as good water solubility, photostability and high stability toward high ionic strength. On the basis of the selective quenching of Hg²⁺ on CuNCs fluorescence, which may be the result of Hg²⁺ ion‐induced aggregation of the CuNCs, the CuNCs was used for the selective and sensitive determination of Hg²⁺ in aqueous solution. The proposed analytical strategy permitted detection of Hg²⁺ in a linear range of 4 × 10^?8 to 6 × 10^?5 M, with a detection limit of 2.2 × 10^?8 M. Eventually, the practicability of this sensing approach was confirmed by its successful application to assay Hg²⁺ in tap water, Lotus lake water and river water samples with the quantitative spike recoveries ranging from 96.9% to 105.4%.     

A new Schiff base as a turn‐off fluorescent sensor for Cu2+ and its photophysical properties

A new Schiff base receptor 1 was synthesized and its photophysical properties were investigated by absorption, emission and excitation techniques. Furthermore, its chromogenic and fluorogenic sensing abilities towards various metal ions were examined. Receptor 1 selectively detects Cu²⁺ ion through fluorescence quenching and detection was not inhibited in the presence of other metal ions. From fluorescence titration, the limit of detection of receptor 1 as a fluorescent ‘turn‐off’ sensor for the analysis of Cu²⁺ was estimated to be 0.35 μM.     

Multimode selective detection of mercury by chiroptical fluorescent sensors based on methionine/cysteine

Two multimode Hg(II) sensors, L‐MethBQA and L‐CysBQA, were obtained by fusing methionine or S‐methyl cysteine, into a bis‐quinolyl amine‐based chiral podand scaffold. Quinolyl groups serve as the fluorophore and possess nitrogen lone pairs capable of chelating metal ions. On exposure to Hg²⁺ or Zn²⁺, these sensors show signal enhancement in fluorescence. However, Cu²⁺ quenches their fluorescence in 30:70 acetontrile/water. L‐CysBQA complexes with Hg²⁺, producing an exciton‐coupled circular dichroism spectrum with the opposite sign to the one that is produced by Cu²⁺ or Zn²⁺ complexation. L‐CysBQA binds Hg²⁺ more strongly than Zn²⁺ and is shown to differentiate Hg²⁺ from other metal ions, such as Zn²⁺, Cu²⁺, Ni²⁺, and Pb²⁺, exceptionally well. The synergistic use of relatively soft sulfur, quinoline‐based chiral ligands and chiroptically enhanced fluorescence detection results in high sensitivity and selectivity for Hg²⁺. Chirality, 2011. © 2011 Wiley‐Liss, Inc.     

A naphthalene derivative as ‘turn‐on’ fluorescent chemosensor for the highly selective and sensitive detection of Al3+

A Schiff base compound derived from naphthalene has been synthesized and characterized as an Al³⁺‐selective fluorescent probe. The chemosensor ( L ) exhibits high selectively for Al³⁺ in aqueous solution, even in the presence of biologically relevant cations such as Na⁺, K⁺, Ca²⁺, Mg²⁺, Pb²⁺ and several transition metal ions. There was no observed interference from anions like Br^?, Cl^?, HSO₃^?, SO₃^2?, S₂O₃^2?, NO₂^?, CO₃^2? and AC^?. The lowest detection limit for the chemosensor L was found to be 1.89 × 10^?8 M with a linear response towards Al³⁺ over a concentration range of 5 × 10^?6 to 4 × 10^?5 M. Furthermore, the proposed chemosensor has been used for imaging of Al³⁺ in two different types of cells with satisfying results, which further demonstrates its value for practical application in biological systems.     

Sensitive and selective detection of Cu(II) ion: A new effective 1,8‐naphthalimide‐based fluorescence ‘turn off’ sensor

The present study reports the development of a new 1,8‐naphthalimide‐based fluorescent sensor V for monitoring Cu(II) ions. The sensor exhibited pH independence over a wide pH range 2.52–9.58, and indicated its possible use for monitoring Cu(II) ions in a competitive pH medium. The sensor also showed high selectivity and sensitivity towards the Cu(II) ions over other competitive metal ions in DMSO–HEPES buffer (v/v, 1:1; pH 7.4) with a fluorescence ‘turn off’ mode of 79.79% observed. A Job plot indicated the formation of a 1:1 binding mode of the sensor with Cu(II) ions. The association constant and detection limit were 1.14 × 10⁶ M^–1 and 4.67 × 10^–8 M, respectively. The fluorescence spectrum of the sensor was quenched due to the powerful paramagnetic nature of the Cu(II) ions. Potential application of this sensor was also demonstrated when determining Cu(II) ion levels in two different water samples.     

Tetrasubstituted cyclopentenone‐based fluorescent chemosensors for the selective detection of Fe3+ and Cu2+ ions

Fluorescent chemosensors based on 4‐hydroxy cyclopentenones were synthesized by the base catalyzed reaction of 1,5‐diphenyl‐pentane‐1,3,5‐trione with benzil and thenil. The molecule obtained by the benzil reaction was found to be useful for the selective detection of Fe³⁺ by fluorescence turn‐off, while the molecule synthesized by the thenil reaction was useful for selective detection of Cu²⁺ by fluorescent turn‐on. Details of the synthesis, complexation mode, nature of binding, reversibility, and pH studies of the two sensors are discussed. The studies revealed that the sensors were suitable for determining Fe³⁺ and Cu²⁺ content in real water samples.     

A highly efficient and selective turn‐on fluorescent sensor for Hg2+, Ag+ and Ag nanoparticles based on a coumarin dithioate derivative

Based on chelation‐enhanced fluorescence, a new fluorescent coumarin derivative probe 3(1‐(7‐hydroxy‐4‐methylcoumarin)ethylidene)hydrazinecarbodithioate for Hg²⁺, Ag⁺ and Ag nanoparticles is reported. Fluorescent probe acts as a rapid and highly selective “off–on” fluorescent probe and fluorescence enhancement by factors 5 to12 times was observed upon selective complexation with Hg²⁺, Ag⁺ and Ag nanoparticles. The molar ratio plots indicated the formation of 1:1 complexes between Hg²⁺ and Ag⁺ with the probe. The linear response range covers a concentration range 0.1 × 10^–5–1.9 × 10^–5 mol/L, 0.1 × 10^–5–2.3 × 10^–5 mol/L and 0.146 × 10^–12–2.63 × 10^–12 mol/L for Hg²⁺, Ag⁺ and Ag nanoparticles, respectively. The interference effect of some anions and cations was also tested. Copyright © 2013 John Wiley & Sons, Ltd.     

A highly selective fluorescent chemosensor for Cu2+: synthesis and properties of a rhodamine B‐containing diarylethene

A diarylethene bearing a triazole‐linked rhodamine B unit was synthesized. Its fluorescent emission was significantly enhanced in the presence of protons or Cu²⁺ due to transformation from the pirocyclic form to open‐ring form. The fluorescence was quenched sequentially upon irradiation with 297 nm light based on the intramolecular fluorescence resonance energy transfer mechanism. In an acetonitrile: water binary solvent (1: 1 v /v), the compound showed significant fluorescent enhancement for Cu²⁺ compared with a wide range of tested metal ions with a fast response and a limit of detection of 2.86 × 10^?8 mol L^?1. Using Cu²⁺ and UV light as the chemical inputs, and fluorescence intensity at 597 nm as the output, a logic gate was developed at the molecular level. Moreover, the compound can be used with a high accuracy to detect Cu²⁺ in a natural water sample.     

Highly selective and sensitive coumarin–triazole‐based fluorometric ‘turn‐off’ sensor for detection of Pb2+ ions

Exposure to even very low concentrations of Pb²⁺ is known to cause cardiovascular, neurological, developmental, and reproductive disorders, and affects children in particular more severely. Consequently, much effort has been dedicated to the development of colorimetric and fluorescent sensors that can selectively detect Pb²⁺ ions. Here, we describe the development of a triazole‐based fluorescent sensor L5 for Pb²⁺ ion detection. The fluorescence intensity of chemosensor L5 was selectively quenched by Pb²⁺ ions and a clear color change from colorless to yellow could be observed by the naked eye. Chemosensor L5 exhibited high sensitivity and selectivity towards Pb²⁺ ions in phosphate‐buffered solution [20 mM, 1:9 DMSO/H₂O (v/v), pH 8.0] with a 1:1 binding stoichiometry, a detection limit of 1.9 nM and a 6.76 × 10⁶ M^?1 binding constant. Additionally, low‐cost and easy‐to‐prepare test strips impregnated with chemosensor L5 were also produced for efficient of Pb²⁺ detection and proved the practical use of this test.     

A carbonothioate‐based highly selective fluorescent probe with a large Stokes shift for detection of Hg2+

Mercury (Hg) is one of the heavy metal pollutants in the environment. Even a very small amount of mercury can cause serious harm to human beings. Herein, we reported a new carbonothioate‐based fluorescent probe for the detection of Hg²⁺ without interference from other metal ions. This probe possessed a very large Stokes shift (192 nm), which could improve the detection sensitivity by minimizing the interferences resulted from self‐absorption or auto‐fluorescence. With the addition of Hg²⁺ to the probe solution, considerable fluorescence enhancement was observed. Additionally, the Hg²⁺ concentration of 0–16 μM and fluorescence intensity showed a good linear relationship (y = 22106× + 53108, R² = 0.9955). Finally, the proposed probe was used to detect Hg²⁺ in real water samples, and its result was satisfactory. Therefore, our proposed probe would provide a promising method for the determination of Hg²⁺ in the environment.     

A Schiff‐based sensor with turn‐on fluorescence for selective detection of Hg2+

A simple Schiff‐base colorimetric receptor 1 was prepared. It exhibits an ‘off–on‐type’ mode with high sensitivity in the presence of Hg²⁺. The change in color is very easily observed by the naked eye in the presence of Hg²⁺, whereas other metal cations do not induce such a change. A Job plot indicated a 1 : 1 complexation stoichiometry between receptor 1 and Hg²⁺. The association constant for 1–Hg²⁺ in Tetrahydrofuran (THF) was determined to be 1.3 × 10⁹ M^‐1 using a Hill plot. Copyright © 2013 John Wiley & Sons, Ltd.     

A highly selective colorimetric and long‐wavelength fluorescent probe for the detection of Hg2+

Currently, the fluorescent probe is an important method for detecting heavy metal ions, especially mercury ion (Hg²⁺), which is harmful to the health of humans and the environment due to its toxicity and extensive use. In this paper, we designed and synthesized a colorimetric and long‐wavelength fluorescent probe Hg‐P with high sensitivity and excellent selectivity, which could detect Hg²⁺ by the changes of visual color, fluorescence and absorption spectroscopy. With the addition of Hg²⁺ to probe Hg‐P solution, its color changed from yellow to pink, and showed a 171 nm red‐shifted absorption spectrum. Probe Hg‐P was used in real water and soil solution samples to detect Hg²⁺, and the result is satisfactory. Therefore, this new probe shows great value and application in detecting Hg²⁺ in the environment.     

Zinc(II)‐selective ratiometric fluorescent probe based on perylene bisimide derivative

A fluorescent probe of N,N′‐biscyclohexyl‐1,7‐di(3‐pyridoxy)‐perylene‐3,4:9,10‐tetracarboxylic acid diimide has been synthesized, and exhibited excellent selectivity and sensitivity for Zn²⁺ over other competing biological cations. The Zn²⁺‐selective fluorescence blue‐shift and enhancing property in conjunction with a visible colorimetric change from orange to green could be observed. With favorable photophysical properties in the visible region, the perylene bisimide derivatives remarkably improved the performance of the probe. Copyright © 2010 John Wiley & Sons, Ltd.     

A highly selective and sensitive 1,8-naphthalimide-based fluorescent sensor for Zn2+ imaging in living cells

A new 4-amino-1,8-naphthalimide-based fluorescent sensor, with iminoacetic acid and iminoethoxyacetic acid as receptor, was developed. It was applied successfully to detect Zn²⁺ in aqueous solution and living cells. Under physiological pH conditions, it demonstrates high selectivity and sensitivity for sensing Zn²⁺ with about 7-fold enhancement in aqueous solution, with a characteristic emission band of 4-amino-1,8-naphthalimide with a green color centered at 550 nm.     

A highly sensitive fluorescent probe for tiopronin based on the cleavage of 2, 4‐dinitrobenzenesulfonate

A highly sensitive fluorogenic probe for tiopronin was proposed. 2,4‐Dinitrobenzenesulfonyl‐fluorescein (I) is an almost nonfluorescent compound. Upon mixing with tiopronin in aqueous solution, the 2,4‐dinitrobenzenesulfonyl group of I was efficiently removed and its parent dye fluorescein was released, hence leading to dramatic increases in both fluorescence and absorbance of the reaction mixture. Under optimal conditions, the fluorescence increase is linear with tiopronin concentration in the range 5.0–600 ng mL^?1, with a detection limit of 1.5 ng mL^?1 (3σ). The proposed method has been successfully applied to tiopronin determination in pharmaceutical preparations and in spiked human urine samples. Copyright © 2009 John Wiley & Sons, Ltd.     

A highly selective and simple fluorescent sensor for mercury (II) ion detection based on cysteamine‐capped CdTe quantum dots synthesized by the reflux method

Cysteamine (CA)‐capped CdTe quantum dots (QDs) (CA–CdTe QDs) were prepared by the reflux method and utilized as an efficient nano‐sized fluorescent sensor to detect mercury (II) ions (Hg²⁺). Under optimum conditions, the fluorescence quenching effect of CA–CdTe QDs was linear at Hg²⁺ concentrations in the range of 6.0–450 nmol/L. The detection limit was calculated to be 4.0 nmol/L according to the 3σ IUPAC criteria. The influence of 10‐fold Pb²⁺, Cu²⁺ and Ag⁺ on the determination of Hg²⁺ was < 7% (superior to other reports based on crude QDs). Furthermore, the detection sensitivity and selectivity were much improved relative to a sensor based on the CA–CdTe QDs probe, which was prepared using a one‐pot synthetic method. This CA–CdTe QDs sensor system represents a new feasibility to improve the detection performance of a QDs sensor by changing the synthesis method. Copyright © 2014 John Wiley & Sons, Ltd.