An aggregation-induced emissive pyridoxal derived tetradentate Schiff base for the fluorescence turn-off sensing of copper(ii) in an aqueous medium

An aggregation-induced emissive pyridoxal derived tetradentate Schiff base was developed for the fluorescence sensing of copper(ii) and sulphide ions.

Hydrazone derivative of 2-hydroxyquinoline-3-carbaldehyde: an efficient anionic and cationic sensor

A hydrazone (1) based on 2-hydroxyquinoline-3-carbaldehyde was synthesized and its anion and cation detection ability were studied. It could detect both fluoride in acetonitrile selectively among anions and copper ions in semiaqueous medium among cations. The addition of fluoride ion to the acetonitrile solution of the receptor produced a sharp colour change from light yellow to bluish green. The corresponding UV–vis measurements showed a red shift of the band of receptor 1 for fluoride and a blue shift of the band for copper ions. The fluorescence intensity of the receptor 1 got quenched with both fluoride and copper ions. The detection limits for both the ions are in order of micromolar level. The practical applications of fluoride detection were extended to oral care products.

A cystine-based dual chemosensor for fluorescent-colorimetric detection of CN- and fluorescent detection of Fe3+ in aqueous media: Synthesis, spectroscopic, and DFT studies

A new dual-responsive chiral cystine based chemosensor, Cys(cou)₂, has been designed and characterized by ¹H NMR, ¹³C NMR, FT-IR, UV-vis as well as elemental analysis. This sensor exhibited an excellent response towards Fe³⁺ and CN^- with high selectivity and sensitivity by fluorescence turn-off mechanism. The binding mode of Cys(cou)₂ with Fe³⁺, and CN^- was confirmed by ESI-MS, ¹H NMR, and fluorescence titration and also quantum chemical calculation. These results showed that the stoichiometric ratio of Cys(cou)₂-Fe³⁺ and Cys(cou)₂-CN is 1:1 and 1:3 in DMSO/Tris aqueous buffer (1:1, v/v), respectively. The linear relationship of the Stern-Volmer plot illustrates the static quenching mechanism at different concentrations. The detection limit (LOD) and binding constant (K_a) for Fe³⁺ and CN^- are 0.029 μM, 1.28 × 10⁴ and 0.51 μM, 9.94 × 10⁶, respectively. Moreover, Cys(cou)₂ can act as a colorimetric sensor for CN^- in DMSO with the color change from colorless to yellow.

Near-infrared fluorescent probe for selective detection of Cu2+ in living cells and in Vivo

A NIR-rhodamine fluorescent probe was designed and successfully synthesized. The structure of the probe NRh-Cu was characterized by ¹H NMR, ¹³C NMR and HRMS. The probe was found to show high sensitivity and high selectivity. The detection limit was calculated to be as low as 0.95 ppb. The sensing mechanism was proposed and confirmed by HRMS spectra. Furthermore, it could be used for imaging Cu²⁺ in living cells and in vivo.

Bifunctional Cu2+/Fe3+ Probe with Independent Signal Outputs Based on a Photochromic Diarylethene with a Dansylhydrazine Unit

A novel dual-response fluorescent sensor based on a diarylethene photoswitching unit and a dansylhydrazine functional group has been synthesized. The compound exhibited high selectivity for Fe³⁺ and Cu²⁺ with independent fluorescence signal outputs. In the presence of Fe³⁺, the sensor formed a 1:1 metal complex, resulting in a remarkable "turn-off" fluorescence signal. On the other hand, its fluorescence intensity was notably enhanced (turn-on) and a color change from bright yellow to bright blue was observed when the sensor interacted with Cu²⁺, which was due to the hydrolysis reaction of the dansyl acid dye, as confirmed by high-resolution mass spectrometry-electrospray ionization and infrared spectrum. The detection limits were 9.73 × 10^-8 mol L^-1 for Fe³⁺ and 3.49 × 10^-7 mol L^-1 for Cu²⁺, respectively. From the unimolecular platform, two molecular logic circuits were constructed using the fluorescence emission intensity at 557/494 nm (Fe³⁺/Cu²⁺) as the outputs and the combined stimuli of Fe³⁺/ethylenediaminetetraacetic acid, Cu²⁺, and UV/vis as the inputs. In addition, the sensor was successfully used to determine Fe³⁺ in water samples from Ganjiang River and soil samples from Nanchang fields.

A highly sensitive luminescent probe based on Ru(II)-bipyridine complex for Cu2+, l-Histidine detection and cellular imaging

A ruthenium(II) bipyridyl complex conjugated with functionalized Schiff base (RuA) has been synthesized and functioned as a luminescent probe. The luminescence of RuA was greatly quenched by Cu²⁺ due to its molecular coordination with paramagnetic Cu²⁺. Subsequently, the addition of l-Histidine can turn on the luminescence of the RuA-Cu(II) ensemble, which can be attributed to the replacement of RuA in RuA-Cu(II) ensemble by l-Histidine. On the basis of the quenching and recovery of the luminescence of RuA, we proposed a rapid and highly sensitive on-off-on luminescent assay for sensing Cu²⁺ and l-Histidine in aqueous solution. Under the optimal conditions, Cu²⁺ and l-Histidine can be detected in the concentration range of 5 nM-9.0 μM and 50 nM-30 μM, respectively, and the corresponding detection limits were calculated to be 0.35 and 0.44 nM (S/N=3), separately. The proposed luminescent probe has been successfully utilized for the analysis of Cu²⁺ and l-Histidine in real samples (drinking water and biological fluids). Furthermore, the probe revealed good photostability, low cytotoxicity and excellent permeability, making it a suitable candidate for cell imaging and labeling in vitro.

A highly selective and sensitive fluorescent probe for Cu2+ based on a novel naphthalimide-rhodamine platform and its application in live cell imaging

Copper plays important roles in a variety of fundamental physiological processes. At the cell organelle level, aberrant copper homeostasis in lysosomes can lead to various serious diseases. Herein, a bifluorophore-based, lysosome-targetable Cu²⁺-selective ratiometric fluorescent probe (V) has been synthesized by reasonable design. The probe V shows high selectivity toward Cu²⁺ ions over other cations and exhibits high sensitivity (1.45 nM) for the detection of Cu²⁺ ions. Meanwhile, the probe is cell permeable and suitable for ratiometric visualization of lysosomal Cu²⁺ in the living cell.

Highly selective and sensitive determination of Cu2+ in drink and water samples based on a 1,8-diaminonaphthalene derived fluorescent sensor

A new simple and efficient fluorescent sensor L based on 1,8‑diaminonaphthalene Schiff-base for highly sensitive and selective determination of Cu²⁺ in drink and water has been developed. This Cu²⁺-selective detection over other tested metal ions displayed an obvious color change from blue to colorless easily detected by naked eye. The detection limit is determined to be as low as 13.2 nM and the response time is very fast within 30 s. The 1:1 binding mechanism was well confirmed by fluorescence measurements, IR analysis and DFT calculations. Importantly, this sensor L was employed for quick detection of Cu²⁺ in drink and environmental water samples with satisfactory results, providing a simple, rapid, reliable and feasible Cu²⁺-sensing method.

Fluorescence “off” and “on” signalling of esculetin in the presence of copper and thiol: a possible implication in cellular thiol sensing

The fluorescence intensity of esculetin was drastically reduced in the presence of a copper ion, which was regenerated in the presence of GSH. The copper–esculetin system was able to detect GSH in a cellular model.

New highly selective turn-on fluorescence receptor for the detection of copper (II)

Three new receptors (1a-c) bearing a p-dimethylaminobenzamide fluorophore have been synthesized and evaluated in terms of their fluoroionophoric properties towards various metal ions. Notably, receptors 1a and 1c exhibited dramatic fluorescent enhancement towards Cu²⁺ in acetonitrile. Subsequent investigations revealed that the highly selective behavior of these receptors towards Cu²⁺ could be attributed to the Cu²⁺-mediated oxidative cyclization of these compounds to the corresponding 1,3,4-oxadiazoles. Solvent effects and quantum calculations indicated that 1a and 1c both possessed an intramolecular charge transfer channel, which could be obstructed by the oxidative cyclization of these receptors. Receptor 1a was successfully applied to the determination of the Cu²⁺ in drug sample with a low detection limit of 2.2×10^-8molL^-1.

A new hydroxynaphthyl benzothiazole derived fluorescent probe for highly selective and sensitive Cu(2+) detection

A new reactive probe, 1-(benzo[d]thiazol-2-yl)naphthalen-2-yl-picolinate (BTNP), was designed and synthesized. BTNP acts as a highly selective probe to Cu(2+) in DMSO/H2O (7/3, v/v, Tris-HCl 10mM, pH=7.4) solution based on Cu(2+) catalyzed hydrolysis of the picolinate ester moiety in BTNP, which leads to the formation of an ESIPT active product with dual wavelength emission enhancement. The probe also possesses the advantages of simple synthesis, rapid response and high sensitivity. The pseudo-first-order reaction rate constant was calculated to be 0.205min(-1). Moreover, application of BTNP to Cu(2+) detection in living cells and real water samples was also explored.

Coumarins as Potential Antioxidant Agents Complemented with Suggested Mechanisms and Approved by Molecular Modeling Studies

Syntheses of coumarins, which are a structurally interesting antioxidant activity, was done in this article. The modification of 7-hydroxycoumarin by different reaction steps was done to yield target compounds. Molecular structures were characterized by different spectroscopical techniques (Fourier transformation infrared and nuclear magnetic resonance). Antioxidant activities were performed by using various in vitro spectrophometric assays against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and hydrogen peroxide (H2O2). All compounds exhibited high efficiency as antioxidants compared to ascorbic acid. The highest efficiency scavenging activity was found for compound 3 (91.0 ± 5.0), followed by compounds 2 and 4 (88.0 ± 2.00; and 87.0 ± 3.00). Ascorbic acid C was used as a standard drug with a percentage inhibition of 91.00 ± 1.5. The mechanism of the synthesized compounds as antioxidants was also studied. Hartree-Fock-based quantum chemical studies have been carried out with the basis set to 3-21G, in order to obtain information about the three-dimensional (3D) geometries, electronic structure, molecular modeling, and electronic levels, namely HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), to understand the antioxidant activity for the synthesized compounds.

A reaction-based fluorescent turn-on probe for Cu2+ in complete aqueous solution

FP can detect Cu²⁺ in complete aqueous solution with a rapid response time, high sensitivity, and high selectivity.

A novel pyrazole biscoumarin based chemosensors for the selective detection of Cu(2+) and Zn(2+) ions

A novel chemosensor based on pyrazole biscoumarin molecule "4-hydroxy-3-((4-hydroxy-2-oxo-2H-chromen-3-yl)(1,3-diphenyl-1H-pyrazol-4-yl)methyl)-2H-chromen-2-one" (PBC) was synthesized by a simple method. The chemosensing properties of PBC towards transition metal ions like Cu(2+) and Zn(2+) by naked eye, UV-Visible and fluorescence spectroscopic methods were described. The PBC solution with Cu(2+) and Zn(2+) ion showed brown and blue colour respectively. The UV-Visible spectra of PBC with Cu(2+) and Zn(2+) ions exposed their corresponding absorption maxima. Further, the Job's plot method confirmed the 1:1 and 2:1 stoichiometry of the complex formation between the PBC with Cu(2+) and Zn(2+) ions respectively. The fluorescence enhancement of PBC on binding with Cu(2+) and Zn(2+) is due to the inhibition of photo induced electron transfer mechanism.

Masking agent-free and channel-switch-mode simultaneous sensing of Fe(3+) and Hg(2+) using dual-excitation graphene quantum dots

A novel channel-switch-mode strategy for simultaneous sensing of Fe(3+) and Hg(2+) is developed with dual-excitation single-emission graphene quantum dots (GQDs). By utilizing the dual-channel fluorescence response performance of GQDs, this strategy achieved a facile, low-cost, masking agent-free, quantitative and selective dual-ion assay even in mixed ion samples and practical water samples.

A well-defined alternating copolymer based on a salicylaldimine Schiff base for highly sensitive zinc(ii) detection and pH sensing in aqueous solution

We report a new strategy to fabricate well-defined alternating Schiff base copolymers of poly(VBCDEG-alt-SaAEMI)s which display two distinguishable color fluorescence “OFF–ON” responses to zinc ions and pH in aqueous solution.

Proton donor modulating ESIPT-based fluorescent probes for highly sensitive and selective detection of Cu2+

Two novel ESIPT-based fluorescent probes for Cu²⁺ detection were developed. Altering the linker in probe molecules reversed their sensing behavior. Both probes exhibited high selectivity and sensitivity to Cu²⁺, and can be used for cell imaging.

Development and cell imaging applications of a novel fluorescent probe for Cu2+

A reactivity-based fluorescent probe was utilized to selectively detecting Cu²⁺ in aqueous solution and living cell.

A self-assembled triphenylamine-based fluorescent chemosensor for selective detection of Fe3+ and Cu2+ ions in aqueous solution

Triphenylamine-based fluorescent chemosensor m-TAPA (S) shows high selectivity and sensitivity toward Fe³⁺/Cu²⁺ in natural and drinking water. Additionally, the TCL strips serve as a simple method for detection of Fe³⁺/Cu²⁺ at the nanomolar range.