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.     

A simply synthesized biphenyl substituted piperidin‐4‐one for the fluorescence chemosensing of Cd2+

Ion‐induced change in fluorescence is a straight‐forward method for detection of toxic metal ions showing immediate response. Cadmium ions are toxic to the environment. We report in this paper a piperidine‐4‐one‐based fluorescent chemosensor of Cd²⁺ ions, designed and synthesized by a simple method. The compound is characterized using infra‐red (IR) and ¹H–NMR spectral techniques. The chemosensor showed Cd²⁺ ion selectivity and sensitivity in aqueous solution. The stoichiometry and the binding constants were determined using fluorescence spectroscopy. Piperidine‐4‐one shows a 1:1 stoichiometric binding to Cd²⁺. The limit of detection of Cd²⁺ was reported.     

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.     

Characterization of a highly Al3+‐selective fluorescence probe based on naphthalimide‐Schiff base and its application to practical water samples

A new fluorescent Al³⁺‐probe, N‐allyl‐4‐[3,3′‐((2‐aminoethyl)azanediyl)‐bis(N´‐(2‐hydroxybenzylidene)propanehy‐drazide)]‐1,8‐naphthalimide ( L ), was designed and synthesized based on 1,8‐naphthalimide. The probe L contains 1,8‐naphthalimide moiety as the fluorophore and a Schiff base as the recognition group. The structure of L was determined by single crystal X‐ray. L emission at 526 nm increased on addition of Al³⁺ under excitation wavelength at 350 nm. L exhibited high selectivity and sensitivity fluorescence emission towards to Al³⁺ in ethanol/Tris–HCl buffer solution (1:1, v/v, pH = 7.2) as compared with other tested metal ions. A good linearity with a correlation coefficient (R²) of 0.99 was observed in the concentration range 2–10 μM. The binding constant and the detection limit of L for Al³⁺ were calculated to 2.6 × 10⁴ M^?1 and 0.34 μM, respectively. The results of experiments that including Job plot, ultraviolet–visible (UV–Vis) light titration, fluorescence titration, ESI‐MS and ¹H NMR titration, indicated a 1:1 stoichiometric complex between L and Al³⁺. L was highly effective in monitoring Al³⁺ in real‐life Yellow River and tap water samples.     

Naked eye sensing of toxic metal ions in aqueous medium using thiophene‐based ligands and its application in living cells

Thiophene‐based diimine (R1) and monoimine (R2) were synthesized in a single step, and their cation binding affinity was tested using colorimetric and UV–vis spectral studies. R1 selectively shows a colorimetric turn‐on response for Pb²⁺, Hg²⁺ ions and colorimetric turn‐off with Sn²⁺ ions, and R2 shows visual response for Cu²⁺ and Hg²⁺ over other examined metal ions in aqueous medium. R1 forms 1:1 complex with Pb²⁺, Hg²⁺, and Sn²⁺ and exhibits fluorescence quenching, whereas R2 shows 2:1 complex with Hg²⁺, Cu²⁺ and shows fluorescence enhancement. The structural and electronic properties of the sensors and their metal complexes were also investigated using Density Functional Theory calculations. R2 was also successfully demonstrated as a fluorescent probe for detecting Cu²⁺ ions in living cells. Copyright © 2014 John Wiley & Sons, Ltd.     

A colorimetric and fluorescent chemosensor for selective detection of Cu2+ based on a new diarylethene with a benzophenone hydrazone unit

A new photochromic diarylethene based on benzophenone hydrazone has been synthesized. Its photochromic and fluorescent properties changed upon alternating irradiation with UV /Vis light and adding Cu²⁺/EDTA in methanol, which showed that the diarylethene could be served as a colorimetric and fluorescent chemosensor for selective detection of Cu²⁺ based on internal charge transfer processes. The colorimetric and turn‐off fluorescent selective detection of Cu²⁺ was attributed to the 2:1 complex of the diarylethene and Cu²⁺. The binding constant (Ka ) was 1.53 × 10⁴ L mol^?1 and the limit of detection of the diarylethene for Cu²⁺ was calculated to be 1.45 × 10^?6 mol L^?1. In addition, the metal‐responsive photochromic behavior of diarylethene was applied successfully to the construction of a molecular logic circuit.     

Water‐soluble polymeric chemosensor for selective detection of Hg2+ in aqueous solution using rhodamine‐based modified poly(acrylamide–acrylic acid)

We report the fabrication of a novel easily available turn‐on fluorescent water‐soluble polymeric chemosensor for Hg²⁺ ions that was simply prepared by micellar free radical polymerization of a water‐insoluble organic rhodamine‐based Hg²⁺‐recognizing monomer (GR6GH), with hydrophilic monomers acrylamide (AM) and acrylic acid (AA). The chemical structure of the polymeric sensor was characterized by FT‐IR and ¹H NMR spectroscopy. The apparent viscosity average molecular weight M_η of poly(acrylamide–acrylic acid) [poly(AM–NaAA)] and the water‐soluble polymeric chemosensor poly(AM–NaAA–GR6GH) were 1.76 × 10⁶ and 6.84 × 10⁴ g/mol, respectively. Because of its amphiphilic property, the water‐soluble polymeric chemosensor can be used as a chemosensor in aqueous media. Upon addition of Hg²⁺ ions to an aqueous solution of poly(AM–NaAA–GR6GH), fluorescence enhancements were observed instantly. Moreover, other metal ions did not induce obvious changes to the fluorescence spectra. This approach may provide an easily measurable and inherently sensitive method for Hg²⁺ ion detection in environmental and biological applications. Copyright © 2015 John Wiley & Sons, Ltd.     

A novel fluorescent probe based on rhodamine hydrazone derivatives bearing a thiophene group for Al3+

In the present work, a novel 5‐methyl‐thiophene‐carbaldehyde‐functionalized rhodamine 6G Schiff base (RA) was designed and easily prepared as an Al³⁺ fluorescent and colorimetric probe, which could selectively and sensitively detect Al³⁺ by showing enhanced fluorescence emission. Meanwhile distinct color variation from colorless to pink also provided ‘naked eye’ detection of Al³⁺, due to the ring spirolactam opening of the rhodamine derivative. Other metal ions (including K⁺, Mg²⁺, Na⁺, Ba²⁺, Mn²⁺, Cd²⁺, Fe²⁺, Ni²⁺, Pb²⁺, Zn²⁺, Hg²⁺, Co²⁺, Li⁺, Sr²⁺ and Cu²⁺) could only induce limited interference. The detection limit of the fluorescent probe was estimated to be 4.17 × 10^?6 M, the binding constant of the RA–Al³⁺ complex was 1.4 × 10⁶ M^?1. Moreover, this fluorescent probe RA possessed high reversibility. As aluminum is a ubiquitous metal in nature and plays vital roles in many biological processes, this chemosensor could be explored for biological study applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Luminescent properties of 4‐aminobenzo‐15‐crown‐5 after preferential binding of ferric ions in aqueous solutions

We report a combined approach that introduces the use of 4‐aminobenzo‐15‐crown‐5 (4AB15C5) for the detection of ferric(III) ions by colorimetric, ultraviolet (UV)–visible light absorption, fluorescence, and live‐cell imaging techniques along with density functional theory (DFT) calculations. We have found that 4AB15C5 is sensitive and selective for binding ferric(III) ions in aqueous solutions. DFT calculations using the polarizable continuum model have been used to explain the strong binding of the ferric ion by 4AB15C5 in aqueous solutions. The detection limit in the fluorescence quenching measurements was found to be as low as 50 μM for the ferric ion with a determined Stern–Volmer constant of 1.52 × 10⁴ M^?1. Fluorescence intensity did not change for other ions tested, Fe²⁺, Co²⁺, Mn²⁺, Mg²⁺, Zn²⁺, Ca²⁺, NH₄⁺, Na⁺, and K⁺ ions. Live‐cell fluorescence imaging was also used to check the intracellular variations in ferric ion levels. Our spectroscopic data indicated that 4AB15C5 can bind ferric ions selectively in aqueous solutions.     

A highly sensitive and reversible chemosensor for Hg2+ detection based on porphyrin‐thymine conjugates

In this study, we demonstrated a highly sensitive, selective, and reversible chemosensor for Hg²⁺ determination. This chemosensor was synthesized by direct condensation of thymin‐1‐ylacetic acid with zinc tetraaminoporphyrin, which has a porphyrin core as the fluorophore and four thymine (T) moieties as the specific interaction sites for Hg²⁺. The probe (4T‐ZnP) exhibited split Soret bands with a small peak at 408 nm and a strong band at 429 nm in a dimethylformamide/H₂O (7/3, v/v) mixed solvent as well as a strong emission band at 614 nm. Upon the addition of Hg²⁺, the probe displayed strong fluorescence quenching due to the formation of T‐Hg²⁺‐T complexes. With the aid of the fluorescence spectrometer, the chemosensor in the dimethylformamide/H₂O (7/3, v/v) mixed solvent (0.3 μM) exhibited a detection limit of 6.7 nM. Interferences from other common cations, such as Co²⁺, K⁺, Sn²⁺, Zn²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Na⁺, Ca²⁺, Mg²⁺, Pb²⁺, and Cd²⁺, associated with Hg²⁺ analysis were effectively inhibited. Copyright © 2015 John Wiley & Sons, Ltd.     

A N‐(2‐hydroxyethyl)piperazine dangled 2,5‐diphenyl‐1,3,4‐oxadiazole‐based fluorescent sensor for selective relay recognition of Cu2+ and sulfide in water

A new 2,5‐diphenyl‐1,3,4‐oxadiazole‐based derivative (L) was synthesized and applied as a highly selective and sensitive fluorescent sensor for relay recognition of Cu²⁺ and S^2? in water (Tris–HCl 10 mM, pH = 7.0) solution. L exhibits an excellent selectivity to Cu²⁺ over other examined metal ions with a prominent fluorescence ‘turn‐off’ at 392 nm. L interacts with Cu²⁺ through a 1:2 binding stoichiometry with a detection limit of 4.8 × 10^–7 M. The on‐site formed L–2Cu²⁺ complex exhibits excellent selectivity to S^2? with a fluorescence ‘off–on’ response via a Cu²⁺ displacement approach. Copyright © 2016 John Wiley & Sons, Ltd.     

A novel optical probe based on d‐penicillamine‐functionalized graphene quantum dots: Preparation and application as signal amplification element to minoring of ions in human biofluid

In this study, d ‐penicillamine‐functionalized graphene quantum dots (DPA‐GQD) has been synthesized, which significantly increases the fluorescence intensity of GQD. We used this simple fluorescent probe for metal ions detection in human plasma samples. Designed DPA‐GQD respond to Hg²⁺, Cu²⁺, Au²⁺, Ag⁺, Co²⁺, Zn²⁺, and Pb²⁺ with high sensitivity. The fluorescence intensity of this probe decreased significantly in the presence of metal ions such as, Hg²⁺, Cu²⁺, Au²⁺, Ag⁺, Co²⁺, Zn²⁺, and Pb²⁺. In this work, a promising probe for ions monitoring was introduced. Moreover, DPA‐GQD probe has been tested in plasma samples. The functionalized DPA‐GQDs exhibits great promise as an alternative to previous fluorescent probes for bio‐labeling, sensing, and other biomedical applications in aqueous solution.     

An OFF–ON–OFF type fluorescent probe based on a naphthalene derivative for Al3+ and F− ions and its biological application

A novel fluorescent probe‐based naphthalene Schiff, 1‐(C2‐glucosyl‐ylimino‐methyl)‐naphthalene‐2‐ol (L) was synthesized by coupling d ‐glucosamine hydrochloride with 2‐hydroxy‐1‐naphthaldehyde. It exhibited excellent selectivity and highly sensitivity for Al³⁺ in ethanol with a strong fluorescence response, while other common metal ions such as Pb²⁺, Mg²⁺, Cu²⁺, Co²⁺, Ni²⁺, Cd²⁺, Fe²⁺, Mn²⁺, Hg²⁺, Li⁺, Na⁺, K⁺, Fe³⁺, Cr³⁺, Zn²⁺, Ag⁺, Ba²⁺ and Ca²⁺ did not cause the same fluorescence response. The probe selectively bound Al³⁺ with a binding constant (K_a) of 5.748 × 10³ M^?1 and a lowest detection limit (LOD) of 4.08 nM. Moreover, the study found that the fluorescence of the L ? Al³⁺ complex could be quenched after addition of F^? in the same medium, while other anions, including Cl^?, Br^?, I^?, NO₂^?, NO₃^?, ClO₄^?, CO₃^2?, HCO₃^?, SO₄^2?, HSO₄^?, CH₃COO^?, PO₄^3?, HPO₄^2?, S^2? and S₂O₃^2? had nearly no influence on probe behaviour. Binding of the [L ? Al³⁺] complex to a F^? anion was established by different fluorescence titration studies, with a detection limit of 3.2 nM in ethanol. The fluorescent probe was also successfully applied in the imaging detection of Al³⁺ and F^? in living cells.     

A new fluorescent chemosensor for Hg2+ in aqueous solution

We prepared an aminothiourea‐derived Schiff base (DA) as a fluorescent chemosensor for Hg²⁺ ions. Addition of 1 equiv of Hg²⁺ ions to the aqueous solution of DA gave rise to an obvious fluorescence enhancement and the subsequent addition of more Hg²⁺ induced gradual fluorescence quenching. Other competing ions, including Pb²⁺, Cd²⁺, Cr³⁺, Zn²⁺, Fe²⁺, Co³⁺, Ni²⁺, Ca²⁺, Mg²⁺, K⁺ and Na⁺, did not induce any distinct fluorescence changes, indicating that DA can selectively detect Hg²⁺ ions in aqueous solution. Copyright © 2012 John Wiley & Sons, Ltd.     

Nitrogen‐doped carbon dots as a fluorescent probe for the highly sensitive detection of Ag+ and cell imaging

An easy hydrothermal synthesis strategy was applied to synthesize green‐yellow emitting nitrogen‐doped carbon dots (N‐CDs) using 1,2‐diaminobenzene as the carbon source, and dicyandiamide as the dopant. The nitrogen‐doped CDs resulted in improvement in the electronic characteristics and surface chemical activities. N‐CDs exhibited bright fluorescence emission and could response to Ag⁺ selectively and sensitively. Other ions produced nearly no interference. A N‐CDs based fluorescent probe was then applied to sensitively determine Ag⁺ with a detection limit of 5 × 10^?8 mol/L. The method was applied to the determination of Ag⁺ dissolved in water. Finally, negligibly cytotoxic, excellently biocompatibile, and highly fluorescent carbon dots were applied for HepG2 cell imaging and the quenched fluorescence by adding Ag⁺, which indicated its potential applications.     

A tricorn‐rhodamine fluorescent chemosensor for detection of Co2+ ions

A novel chemosensor TrisRh based on tris(2‐aminoethyl)amine and rhodamine 6G is designed and synthesized as a fluorescence turn‐on probe for Co²⁺ ions that is paramagnetic with a property of quenching fluorescence. Rhodamine spirolactam forms are nonfluorescent, whereas, ring‐opening of corresponding spirocyclic induced by Co²⁺ results in strong fluorescence emission. Upon the addition of Co²⁺ ions, TrisRh can display significant enhancements in absorbance and fluorescence intensity as well as evident colorific transformation, which can be perceived by the naked eye. The association stoichiometry of TrisRh to Co²⁺ ions was inferred to be 1:1 through Job's plot and electrospray ionization mass spectrometry analysis. The binding model was speculated from Fourier transform infrared spectra and ¹H–nuclear magnetic resonance technologies. Significantly, the limit of detection was determined to be as low as 1.22 nmol. Furthermore, TrisRh can exhibit robust anti‐jamming ability against other interference metal ions.     

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.     

A new fluorescent chemosensor for cadmium(II) based on a pyrene‐appended piperidone derivative and its β‐cyclodextrin complex

We report, in this article, a piperidin‐4‐one derivative carrying pyrenyl fluorescent reporter groups which acts as a Cd²⁺ ion sensor. The compound is synthesized and characterized using IR and NMR spectral techniques. The compound forms an inclusion complex with β‐cyclodextrin. It selectively binds to Cd²⁺ ions in water and aqueous β‐cyclodextrin media. The stoichiometry of the host–guest complex of the compound with β‐cyclodextrin is 1:2. The ligand–metal ion binding stoichiometry is 1:1 both in water and in β‐cyclodextrin. The linear concentration range of detection of the metal ion is reported. Cyclodextrin complex formation does not affect the metal ion selectivity of the compound.     

Fluorescent sensors based on quinoline‐containing styrylcyanine: determination of ferric ions,hydrogen peroxide,and glucose,pH‐sensitive properties and bioimaging

A novel styrylcyanine‐based fluorescent probe 1 was designed and synthesized via facile methods. Ferric ions quenched the fluorescence of probe 1, whereas the addition of ferrous ions led to only small changes in the fluorescence signal. When hydrogen peroxide was introduced into the solution containing probe 1 and Fe²⁺, Fe²⁺ was oxidized to Fe³⁺, resulting in the quenching of the fluorescence. The probe 1/Fe²⁺ solution fluorescence could also be quenched by H₂O₂ released from glucose oxidation by glucose oxidase (GOD), which means that probe 1/Fe²⁺ platform could be used to detect glucose. Probe 1 is fluorescent in basic and neutral media but almost non‐fluorescent in strong acidic environments. Such behaviour enables it to work as a fluorescent pH sensor in both the solution and solid states and as a chemosensor for detecting volatile organic compounds with high acidity and basicity. Subsequently, the fluorescence microscopic images of probe 1 in live cells and in zebrafish were achieved successfully, suggesting that the probe has good cell membrane permeability and a potential application for imaging in living cells and living organisms. Copyright © 2014 John Wiley & Sons, Ltd.     

Three‐dimensional (3‐D) fluorescence spectroscopy analysis of the fluorescent dissolved organic matter released by the marine toxic dinoflagellate Alexandrium catenella exposed to metal stress by zinc or lead

We investigated the effects of zinc or lead on growth and on exudation of fluorescent dissolved organic matter (FDOM) by the marine toxic dinoflagellate Alexandrium catenella (Whedon & Kofoid) Balech. The species was exposed to increasing free zinc (1.34 × 10^?7 M–3.98 × 10^?6 M) or lead (5.13 × 10^?9 M–1.82 × 10^?7 M) concentra‐tions. Low metal levels ([Zn²⁺] = 1.34 × 10^?7 M; [Pb²⁺] = 5.13 × 10^?9 M) had no effect on cell growth. Toxic effects were observed from higher metal contamination ([Zn²⁺] = 3.98 × 10^?6 M; [Pb²⁺] = 6.54 × 10^?8 M), as a conversion of vegetative cells into cysts. Analysis of the released FDOM by three‐dimensional (3‐D) fluorescence spectroscopy was achieved, using the parallel factor analysis (PARAFAC). The PARAFAC modeling revealed four components associated with two contributions: one related to the biological activity; the other linked to the organic matter decomposition in the culture medium. The C1 component combined a tryptophan peak and characteristics of humic substances, whereas the C2 component was considered as a tryptophan protein fluorophore. The two others C3 and C4 components were associated with marine organic matter production. Relea‐sed fluorescent substances were induced by low ([Zn²⁺]= 1.34 × 10^?7 M; [Pb²⁺] = 5.13 × 10^?9 M) and moderate ([Zn²⁺] = 6.21 × 10^?7 M; [Pb²⁺] = 2.64× 10^?9 M) metal concentrations, suggesting the activation of cellular mechanisms in response to metal stress, to exudate FDOM that could complex metal cations and reduce their toxicity toward A. catenella cells.