A coumarin-based fluorescent probe for selective detection of Cu2+ in water

Fluorescent Red GK, a commercially available coumarin-based dye, was developed as a “turn-off” fluorescent probe for detection of Cu²⁺ in aqueous solution. It exhibited high selectivity and sensitivity at room temperature. Upon addition of Cu²⁺, the strong fluorescence of Fluorescent Red GK was severely quenched and its color changed from orange to colorless under illumination with a UV lamp; the color of the solution also changed from pink to colorless. So, it can be used as a specific colorimetric and fluorescent probe for Cu²⁺ with a detection limit as low as 0.0634?μM.     

Bifunctional probe for Cu2+/Al3+ based on a diarylethene with a 4, 5-[bis-(5-ethylacetate-yl)-2-thienyl]-1H-imidazole unit

A new asymmetric perfluordiarylethene (1O) was synthesized using 4, 5-[bis-(5-ethylacetate-yl)-2-thienyl]-1H-imidazole as a functional group. 1O exhibited favorable reversible cyclization and cycloreversion reactions upon alternating irradiation with UV and visible light. Both of its open- and closed-ring isomers were found to be highly selective towards Cu²⁺ with significant absorption and color changes, which could be used as a ‘naked-eye’ colorimetric sensor for Cu²⁺ detection. Upon exposure to acid, its fluorescence dramatically enhanced by 14-fold with a color change from dark to bright cyan due to the formation of the protonated compound. Moreover, 1O showed obvious fluorescence “turn-on” signal response towards Al³⁺, and the detection limit for Al³⁺ was determined to be 4.8 × 10^?9 mol L^?1. Based on the fluorescence signals of 1O, a combinational stimuli logic circuit were designed by using the fluorescence intensity as the output signal with the inputs of lights, Al³⁺ and EDTA. Finally, 1O could be used as a biological probe for detecting intracellular Al³⁺ in a physiological environmental.     

A fluorescent chemosensor for Cu2+ ions and its application in cell imaging

A new on-off fluorescent probe 1 for Cu²⁺ based on Schiff base compound was designed and synthesized by one-step reaction. The single probe 1 exhibited strong green fluorescence emission. A fluorescence quenching effect and faint color change were observed as soon as the Cu²⁺ was added to the probe system in H₂O/EtOH (v/v = 8:2, HEPES buffer, 0.05 M, pH = 7.4) solution. Other common metal cations did not cause the changes in the fluorescence and color of the probe 1. The optical properties were studied by the fluorescence emission and UV–Vis spectra. Meanwhile, the geometry optimizations of probe 1 and the [1-Cu²⁺] coordination complexes were also carried out by DFT using the Gaussian 09 program, in which the B3LYP function was used. Based on experimental measurement and theoretical analysis, we can know that the combination ratio of the probe and Cu²⁺ is 2:1 and the limit of detection (LOD) is as low as 5.3 × 10^?9 M Besides, the probe 1 was also used to analyze the Cu²⁺ in living cells.     

A Highly Selective Colorimetric Sensor for Cu2+ Based on Phenolic Group Biscarbonyl Hydrazone

A novel copper selective sensor 2 based on hydrazide and salicylaldehyde has been designed and prepared. Sensor 2 behaves a single selectivity and sensitivity in the recognition for Cu²⁺ over other metal ions such as Fe³⁺, Hg²⁺, Ag⁺, Ca²⁺, Zn²⁺, Pb²⁺, Cd²⁺, Ni²⁺, Co²⁺, Cr³⁺ and Mg²⁺ in DMSO. The distinct color change and the rapid changement of fluorescence emission provide naked‐eyes detection for Cu²⁺. The UV‐vis data indicate that 1:2 stoichiometry complex is formed by sensor 2 and Cu²⁺. The association constant K_s was 3.51×10⁴ mol^?1·L. The detection limitation of Cu²⁺ with the sensor 2 was 2.2×10^?7 mol·L^?1. The sensing of Cu²⁺ by this sensor was found to be reversible, with the Cu²⁺‐induced color being lost upon addition of EDTA.     

A novel lipid droplets-targeting fluorescent probe based on dicyanisophorone and carbazole for Cu2+ and its application

A novel fluorescent probe, LCH , based on dicyanisophorone and carbazole, was prepared for the visual detection of Cu²⁺. The probe LCH could recognize Cu²⁺ by fluorescence quenching in EtOH/H₂O (1/4, v/v) solution, which could be easily identified under the 365 nm UV lamp, and the detection limit was as low as 0.785 μM. The recognition mechanism of probe LCH with Cu²⁺ was determined by combining ¹H NMR titration, MS, and theoretical calculations. Practical application experiments showed that probe LCH could be used to detect Cu²⁺ in the test strip experiments. Cell imaging experiments showed that the probe LCH owned good cell permeability and could be applied to the imaging of Cu²⁺ in HepG2 cells. In addition, fluorescence colocalization experiments showed that LCH could target lipid droplets. These results indicate that the probe LCH will have a good application prospect in environmental detection and clinical medicine.     

Carbazole‐based colorimetric and fluorescent probe for Cu2+ and its utility in bio‐imaging and real water samples

A new carbazole functionalized Schiff base CBM was synthesized and characterized. CBM can selectively recognize Cu²⁺ via UV–vis and fluorescence signal among common biologically relevant metal ions. When Cu²⁺ was added to CBM, there was a significant enhancement at the maximum absorption wavelength of 393 nm and with a distinct blue shift. The maximum emission peak was significantly attenuated by a factor of about 15 times at 535 nm and the blue shift of emission wavelength was observed. When other metal ions were added, there was no remarkable change at the maximum absorption and emission peak. Under the illumination of 365 nm ultraviolet lamp, the color of the CBM solution changed from light blue to dark blue after the addition of Cu²⁺. The combination mechanism of CBM with Cu²⁺ was nicely explored by density functional theory studies. The probe CBM has good cell permeability, fluorescence electron microscopy experiments show that CBM can be used as a fluorescent probe to detect the presence or absence of Cu²⁺ in Hela cells. Furthermore, the probe CBM can also be used for the detection of copper ions in actual water samples.     

Catching S2− and Cu2+ by a highly sensitive and efficient salamo-like fluorescence-ultraviolet dual channel chemosensor

Abstract

A highly sensitive and efficient fluorescence-ultraviolet dual channel chemical sensor H₂L based on the salamo-like bisoxime (6,6′-dimethoxy-2, 2′-[ethylenediyldioxybis(nitrilomethylidyne)]diphenol) was synthesized, Cu²⁺ and S^2? ions can be detected respectively. For the identification of metal cations, the Cu²⁺ can quench the fluorescence intensity of probe H₂L at the excitation wavelength of 311?nm, and when the same equivalent of EDTA was added, the fluorescence intensity of L-Cu complex returned to its original intensity practically, completing the fluorescence “OFF-ON-OFF” cycle after adding the same amount of Cu²⁺ again. The mechanism was confirmed by high resolution mass spectrometry, and it was concluded that the probe H₂L and Cu²⁺ formed a complex. For the identification of anions, UV–Vis spectral identification and naked-eye recognition for S^2? were performed. The binding mode of the probe to the sulfur anion and the recognition mechanism were confirmed by ¹H NMR titration. In addition, the probe H₂L showed high selectivity and sensitivity to Cu²⁺ and S^2?, the detection limits of L-Cu and L-S systems toward Cu²⁺ and S^2? are 46 and 25?nM respectively. In terms of application, the content of Cu²⁺and S^2? in different water samples (distilled water, Yellow River water and tap water) with probe H₂L was successfully tested. These results indicated that the probe H₂L can be used as a highly selective and sensitive dual channel sensor to detect both Cu²⁺ and S^2? ions in the environment and biological systems.     

A new Schiff base fluorescent indicator for the detection of Mg<Superscript>2+</Superscript> and its application to real samples

A new Schiff base fluorescence probe, 3-Allylsalicylaldehyde salicylhydrazone (L), for Mg²⁺ was designed and synthesized. The fluorescence of the sensor L was enhanced remarkably by Mg²⁺ with 2:1 binding ratio, and the binding constant was determined to be 1.02 × 10⁷ M^?1. Probe L had high sensitivity for Mg²⁺ in a solution of DMF/water (4:1, v/v, pH 7.5), and the detection limit was 4.88 × 10^?8 mol/L. Common coexistent metal ions, such as K⁺, Na⁺, Ag⁺, Ca²⁺, Zn²⁺, Ba²⁺, Bi²⁺, Cu²⁺, Ni²⁺, Hg²⁺, Fe³⁺ , and Al³⁺, showed little or no interference on the detection of Mg²⁺ in solution. The fluorescence probe L, which was successfully used for the determination of trace Mg(II) in real samples, was shown to be promising for liquid-phase extraction coupled with fluorescence spectra.     

A Chromo-Fluorogenic Naphthoquinolinedione-Based Probe for Dual Detection of Cu2+ and Its Use for Various Water Samples

The presence of an abnormal amount of Cu²⁺ in the human body causes various health issues. In the current study, we synthesized a new naphthoquinolinedione-based probe (probe 1) to monitor Cu²⁺ in different water systems, such as tap water, lakes, and drain water. Two triazole units were introduced into the probe via a click reaction to increase the binding affinity to a metal ion. In day-light, probe 1 dissolved in a mixed solvent system (HEPES: EtOH = 1:4) showed a vivid color change from light greenish-yellow to pink in the presence of only Cu²⁺ among various metal ions. In addition, the green luminescence and fluorescence emission of the probe were effectively bleached out immediately after Cu²⁺ addition. The limit of detection (LOD) of the probe was 0.5 µM when a ratio-metric method was used for metal ion detection. The fluorescence titration data of the probe with Cu²⁺ showed a calculated LOD of 41.5 pM. Hence, probe 1 possesses the following dual response toward Cu²⁺ detection: color change and fluorescence quenching. Probe 1 was also useful for detecting Cu²⁺ spiked in tap/lake water as well as the cytoplasm of live HeLa cells. The current system was investigated using ultraviolet-visible and fluorescence spectroscopy as well as density functional theory calculations (DFT).     

Single chemosensor for multiple analytes: chromogenic and fluorogenic detection for fluoride anions and copper ions

A o-hydroxybenzoyl-(N-butyl-4,6-naphthamimide) hydrazone (1) has been synthesized. Compound 1 displayed high selectivity for F^? and Cu²⁺ with UV/vis absorption and fluorescence spectra, respectively. In the presence of F^?, while the absorption peak of 1 showed the red shift, its fluorescent intensity decreased due to deprotonation interaction. In the presence of Cu²⁺, both the absorption and fluorescence peaks decreased because of the coordination interaction.     

A reversible fluorescence “ON–OFF–ON” sensor for sequential detection of F− and Cu2+ ions and its application as a molecular-scale logic device and security keypad lock

A new azoimine receptor, R₁, was synthesized by Schiff base condensation of 4-(4-butylphenyl) azophenol and 2,6-diaminopyridine and acts as a colorimetric and fluorometric chemosensor for F^? and also toward Cu²⁺ ions in aqueous environment. UV–Vis absorption and fluorescent emission spectra were employed to study the sensing process. Emission study was performed to examine the dual sensing ability of the obtained probe with sequential addition of F^? followed by Cu²⁺ and vice versa. The receptor is an efficient “ON–OFF” fluorescent probe for the fluoride ion. Also, R₁ + F^? operated as an “OFF–ON” fluorescent sensor for Cu²⁺ ions. Considering emission intensity and absorption wavelength for F^? and Cu²⁺ ions, a molecular system was developed with the ability to mimic the functions of XNOR logic gating on the molecular level. In addition, R₁ behaved as a molecular security keypad lock with F^? and Cu²⁺ inputs. The keypad lock operation is particularly important, as the output of the system depends not only on the proper combination but also on the order of input signals, creating the correct password that can be used to “open” this molecular keypad lock through strong fluorescence emission at 460?nm.     

A colorimetric squaraine-based probe and test paper for rapid naked eyes detection of copper ion (II)

A colorimetric probe N,N’-bis(2-methoxy-ethyl)-2,3,3-trimethyl-3H-squaraine (MOESQ) with H₂O solubility was synthesized to detect Cu²⁺. MOESQ exhibits good selectivity, high sensitivity and fast UV-Vis response toward Cu²⁺ over other competing ions in CH₃CN. The detection limit of MOESQ for Cu²⁺ in CH₃CN can reach 1.88?×?10^?7?molL^?1. By adsorbing MOESQ on the chromatography paper, a colorimetric test paper for Cu²⁺ was prepared, which could detect Cu²⁺ with the color change from blue to faint yellow even in the limit of detection concentration of 10^?6?molL^?1.     

A highly selective fluorescence switch for Cu2+ and Fe3+ based on a new diarylethene with a triazole-linked rhodamine 6G unit

A new diarylethene compound with a triazole-linked rhodamine 6G unit attached to the imino group (1O) was designed and synthesized. According to the test results, the solution color and fluorescence color of diarylethene can be modulated by lights and metal ions. The solution color could change from colorless to light purple when irradiated with UV light. When Cu²⁺ was added to the diarylethene solution, the color of diarylethene solution became blue, the fluorescence color turned from dark to bright yellow. Although the solution color did not change by adding Fe³⁺, its fluorescence color varied from dark to yellow. Moreover, it was found that the complex ratio of the diarylethene to Cu²⁺ was 1:1 and the binding stoichiometry of the diarylethene to Fe³⁺ was also 1:1 based on the data of NMR, MS, and other experiments. Based on these findings, photochromic figure of the diarylethene with UV/Vis light, Cu²⁺ and Fe³⁺ was constructed. Furthermore, the logic circuit was designed by input signals (ultraviolet stimulus, visible light stimulus, Cu²⁺ (or Fe³⁺) and EDTA) and an output signal (fluorescent intensity at 566?nm (or 575?nm)).     

Probing phosphate ion via the europium(III)-modulated fluorescence of gold nanoclusters

Fluorescent gold nanoclusters (Au-NCs) were synthesized by a one-pot method using 11-mercaptoundecanoic acid as a reducing and capping reagent. It is found that the red fluorescence of the Au-NCs is quenched by the introduction of Eu(III) at pH 7.0, but that fluorescence is restored on addition of phosphate. The Au-NCs were investigated by transmission electron microscopy and fluorescence photographs. The effect of pH on fluorescence was studied in the range from pH 6 to 10 and is found to be strong. Based on these findings, we have developed an assay for phosphate. Ions such as citrate, Fe(CN)₆ ^3?, SO₄ ^2?, S₂O₈ ^2?, Cl^?, HS^?, Br^?, AcO^?, NO₂ ^?, SCN^?, ClO₄ ^?, HCO₃ ^?, NO₃ ^?, Cd²⁺, Ba²⁺, Zn²⁺, Mg²⁺, and glutamate do not interfere, but ascorbate and Fe³⁺ can quench Au-NCs fluorescence. The fluorescent nanocluster probe responds to phosphate in the range from 0.18 to 250 μM, and the detection limit is 180 nM. The probe also responds to pyrophosphate and ATP. Figure

Off/on fluorescence sensor for phosphate based on Eu³⁺-modulated Au NCs thanks to the competition of oxygen-donor atoms from phosphate with those from the carboxylate groups was developed     

A fluorescent probe for copper and hypochlorite based on rhodamine hydrazide framework

A rhodamine derivative (1) was synthesized as a fluorescence turn-on probe for copper (Cu²⁺) and hypochlorite (ClO^?). The probe gave a fluorescence turn-on change at 587 nm with a color change from colorless to pink in the presence of Cu²⁺ or ClO^? ions in aqueous solution. It was found that the Cu²⁺ ion bound to 1 in a 1:1 stoichiometry and induced a spirolactam ring opening of the rhodamine moiety leading to a fluorescence turn-on, confirmed by Job’s plot, ESI-Mass, and ¹H NMR analyses. In the presence of ClO^? ion, probe 1 underwent a hypochlorite-mediated oxidation and hydrolysis to produce a ring-opened rhodamine B with a fluorescence enhancement. However, these changes were not monitored in case of other metal ions, anions, and reactive redox species. In addition, probe 1 can readily react with the ClO^? to provide a distinct fluorescence enhancement along with a pink color even in the presence of various competitive species.     

A coumarin based highly selective fluorescent chemosensor for sequential recognition of Cu2+ and PPi

In this study, we have successfully synthesized a new coumarin based fluorescent chemosensor 1, in which tren and quinolone are introduced as receptors for sequential recognition of Cu²⁺ and PPi. The structure of chemosensor 1 was characterized by ¹H NMR, ¹³C NMR and ESI-HR-MS. Sensor 1 showed an obvious “on-off” fluorescence quenching response toward Cu²⁺, and the quenching efficiency reached a maximum of 99.6% with the addition of 20 equiv. of Cu²⁺. The 1-Cu²⁺ complex showed an “off-on” fluorescence enhancement response toward PPi over many competitive anions, especially HPO₄^2? and H₂PO₄^?. The detection limit of sensor 1 was 1.9?×?10^?6?M to Cu²⁺ and 5.96?×?10^?8?M to PPi. In addition, sensor 1 showed a 1:1 binding stoichiometry to Cu²⁺ and sensor 1-Cu²⁺ showed a 2: 1 binding stoichiometry to PPi in CH₃CN/HEPES buffer medium (9:1 v/v, pH?=?7.4). The stable pH range of sensor 1 to Cu²⁺ and 1-Cu²⁺ to PPi was from 4 to 8.     

Unique Fluorogenic Ratiometric Fluorescent Chemodosimeter for Rapid Sensing of CN− in Water

A new benzimidazole‐spiropyran conjugate chemosensor molecule ( BISP ) has been synthesized and characterized by ¹H NMR spectroscopy, mass spectrometry (ESI‐MS), and elemental analysis. The two isomeric forms ( BISP ? BIMC ) were shown to be highly selective and sensitive to CN^? among the ten anions studied in aqueous HEPES buffer, as shown by fluorescence and absorption spectroscopy and even by visual color changes, with a detection limit of 1.7 μM for BIMC . The reaction of CN^? with BIMC was monitored by ¹H NMR spectroscopy, high‐resolution mass spectrometry (HRMS), UV/Vis measurements, and fluorescence spectroscopy in HEPES buffer of pH 7.4. TDDFT calculations were performed in order to correlate the electronic properties of the chemosensor with its cyanide complex. Further, titration against thiophilic metal ions like Au³⁺, Cu²⁺, Ag⁺, and Hg²⁺ with [ BIMC‐CN ] in situ showed that it acts as a secondary recognition ensemble toward Au³⁺ and Cu²⁺ by switch‐on fluorescence. In addition, a reversible logic‐gate property of BIMC has been demonstrated through a feedback loop in the presence of CN^? and Au³⁺ ions, respectively. Furthermore, the use of BIMC to detect CN^? in live cells by fluorescence imaging has also been demonstrated. Notably, test strips based on BIMC were fabricated, which could serve as convenient and efficient CN^? test kits.     

A highly sensitive naphthalimide-based fluorescent probe for detection of Cu2+ via selective hydrolysis reaction and its application in practical samples

A novel fluorescent probe CN3, containing 1,8-naphthalimide and picolinate units, was synthesized, and its structure was characterized by ¹H nuclear magnetic resonance spectroscopy (H NMR), ¹³C nuclear magnetic resonance spectroscopy (C NMR), and mass spectroscopy techniques. The detection property of CN3 toward copper ions (Cu²⁺) has been investigated in ethanol–HEPES buffer (v/v = 1/1, pH = 7.40) solution by UV–Vis absorption and fluorescence emission spectra. The results showed that CN3 had a highly selective and sensitive fluorescence quenching response to Cu²⁺, which was attributed to the generation of weak fluorescent N-ethyl-4-hydroxyphenyl-1,8- naphthalimide (compound 2) in polar ethanol–HEPES buffer (v/v = 1/1, pH = 7.40) via selective hydrolysis reaction. The detection of CN3 for Cu²⁺ was not influenced in the presence of other competing metal ions, and the limit of detection was as low as 50.0 nM. Therefore, the color of CN3 changed from colorless to yellowish when the Cu²⁺ was added. Furthermore, the fluorescent probe CN3 was utilized to detect Cu²⁺ in real water samples with fine performance.     

2-(2′-Hydroxyphenyl)-4(3H)-quinazolinone derivatives based fluorescent probes for mercury(II) via an intramolecular proton transfer mechanism

2-(2′,5′-Dihydroxy-phenyl)-4(3H)-quinazolinone (DHPQ), a new fluorescent dye that exhibits excited state intramolecular proton transfer (ESIPT) reaction and possesses good photophysical properties, is synthesised and used as fluorescent probe for detection of Hg²⁺. Mercuric ions can be detected and quantitated by measuring the fluorescent intensity decrease of the probe. The decrease of fluorescence intensity of DHPQ upon the addition of Hg²⁺ was attributed to the blocking of ESIPT reactions of DHPQ and quenching its fluorescence. The analytical performance characteristics of the proposed Hg²⁺ probe were investigated. The probe can be applied to the quantification of Hg²⁺ with a concentration range covering from 8.0?×?10^?7 to 2.0?×?10^?4?mol?L^?1, with a working pH range of 5.5–6.5. It shows excellent selectivity for Hg²⁺ over other transition metal cations. The proposed method was testified for the Hg²⁺ assay in river water samples with satisfying recoveries.     

Characterization of rhodamine B hydroxylamide as a highly selective and sensitive fluorescence probe for copper(II)

Rhodamine B hydroxylamide (1) is characterized as a highly selective and sensitive fluorescence probe for Cu²⁺. Under the optimized conditions, the probe exhibits specific absorbance-on and fluorescence-on responses to Cu²⁺ only. This remarkable property may allow Cu²⁺ to be detected directly in the presence of the other transition metal ions, and such an application has been demonstrated to human serum. The reaction mechanism is also investigated and proposed as that the hydroxylamide group of 1 binds Cu²⁺, and the subsequent complexation of Cu²⁺ displays a high catalytic activity for the hydrolytic cleavage of the amide bond, causing the release of fluorophore (rhodamine B) and thereby the retrievement of absorbance and fluorescence. The recovered fluorescence intensity is proportional to the concentration of Cu²⁺ in the range 1-20 μM. The detection limit for Cu²⁺ is 33 nM (k = 3). The reaction mechanism described here may be useful for developing excellent spectroscopic probes with cleavable active bonds for other analytes.