A fluorescent probe based on N-butylbenzene-1,2-diamine for Cu(II) and its imaging in living cells

A fluorescent probe LZ-N with naphthalimide as fluorophore and N-butylbenzene-1,2-diamine as a new recognition moiety for copper ion was designed and synthesized. The probe LZ-N exhibits high selectivity for Cu²⁺ ion in aqueous media (CH₃CN:H₂O = 1:1) over all the other metal ions in our study, more than 20-fold fluorescence enhancement by coordinating with Cu²⁺, and the maximum emission intensity independence in the range of pH 2.06–9.25. The results of ¹H-NMR titration, time-resolved fluorescence decay measurement, and computational optimization illuminate the mechanisms of Cu²⁺ and probe LZ-N. Confocal fluorescence images and cell viability values test show the high fluorescence enhancement of probe LZ-N for exogenous Cu²⁺ in living cells.     

A novel turn-on fluorescent probe for Hg2+ detection based on rhodamine B spirolactam derivative

ABSTRACT

In this work, a new turn-on fluorescent probe 1 for Hg²⁺ ions detection based on rhodamine B spirolactam was reported. Among tested metal ions, probe 1 shows high selectivity towards Hg²⁺ in the the mixture solution of methanol and 0.02 M HEPES buffer (V/V = 9:1, pH = 7.2). No absorption and emission band of probe 1 was observed in the range from 450 to 700 nm. While only addition of Hg²⁺ to probe 1 could lead to appearance of a new absorption band centered at 553 nm and a fluorescence emission band around 577 nm upon excitation at 520 nm. Moreover, it exhibits excellent linear relationship (R² = 0.9993) between fluorescence intensity at 577 nm and the concentration of Hg²⁺ from 1.6 to 32 μM. The sensing mechanism was proven to be spirolactam ring open induced by Hg²⁺ through ¹H NMR, MS, absorption and fluorescence spectra. In addition, probe 1 could detect Hg²⁺ in real water samples and on filter paper, which demonstrates its application in environment science.     

A dual chemosensor for Cu2+ and Fe3+ based on π-extend tetrathiafulvalene derivative

A new dual chemosensor (TTF-PBA) for Fe³⁺ and Cu²⁺ in different signal pathways was designed and synthesized. The absorption spectrum, fluorescence spectrum and cyclic voltammograms changed in the presence of Cu²⁺ and Fe³⁺. The optical color changed within 5 s from yellow to orange upon the addition of Cu²⁺, and it changed to dark yellow when Fe³⁺ existed. The cyclic voltammogram of Cu²⁺/TTF-PBA changed from E_ox = 0.50 V, E_red = 0.32 V to E_ox = 0.64 V, E_red = 0.80 V (vs Ag/AgCl) upon the addition of 2.0 equiv. Cu²⁺. As for Fe³⁺/TTF-PBA, its oxidation wave disappeared, and its reduction wave appeared at E_red = ?0.59 V (vs Ag/AgCl) upon the addition of 4.0 equv. Fe³⁺. The sensor displayed high selectivity for Cu²⁺ and Fe³⁺ over other ions including Pb²⁺, Zn²⁺, Ni²⁺, Ag⁺, Cr³⁺, Mn²⁺, Al³⁺, Co²⁺, Pd²⁺, Hg²⁺, Fe^2+, Cd²⁺, Ce³⁺, Bi³⁺ and Au³⁺, the detection limits for Cu²⁺ and Fe³⁺ ion reached as low as 5.33 × 10^?7 mol/L and 5.34 × 10^?7 mol/L, respectively. Furthermore, when Fe³⁺ existed, Cu²⁺ can be detected sequentially by the sensor through the absorption spectrum and the color change observed by naked-eyes.     

Cu2+-selective turn-on fluorescence signaling based on metal-induced hydrolysis of pyrenecarbohydrazide

We developed a simple Cu²⁺-selective turn-on fluorescence signaling probe based on the hydrolysis of 1-pyrenecarbohydrazide (1) to 1-pyrenecarboxylic acid. Probe 1 exhibited prominent fluorescence signaling of Cu²⁺ ions in a 10% aqueous Tris-buffered (pH 7.0) DMSO solution with a detection limit of 5.93 × 10^?8 M. Signaling with control compounds derived from pyreneacetic acid and pyrenebutyric acid showed that the fluorescence signal became less pronounced as the distance between the hydrazide functionality and the pyrene fluorophore increased. As a practical application, this probe was employed for the determination of Cu²⁺ in a simulated semiconductor wastewater.     

Naked-eye detection of Cu (II) and Fe (III) based on a Schiff Base Ruthenium complex with nicotinohydrazide

A cyclometalated ruthenium (II) complex 1 [(Ru (Phen)₂(Pbznh)]⁺ PF₆⁻ (Phen = 1,10-phenanthroline and Pbznh = N-(4-(pyridine-2-yl)benzylidene) nicotinohydrazide) with nicotinohydrazide as a functional group was synthesized and characterized. Changes of its absorption spectra and color induced by Cu²⁺ and Fe³⁺ were systematic investigated. The results demonstrated that complex 1 could be served as a colorimetric probe to fast, selective and sensitive detection of Cu²⁺ and Fe³⁺ both in acetonitrile and filter paper based strips. Upon addition of Cu²⁺ and Fe³⁺ to solution of probe 1 , solution color changed from pink to colorless and light yellow respectively, and their corresponding detection limit were calculated to be 3.26 × 10⁻⁸ M and 3.12 × 10⁻⁷ M. Moreover, color of test papers with 1 changed from pink to colorless/yellow when Cu²⁺/Fe³⁺ were dropwise added. Therefore, it can be used as a desirable ‘naked-eye’ indicator candidate for Cu²⁺ and Fe³⁺.     

Novel 1,8-naphthalimide dye for multichannel sensing of H<Superscript>+</Superscript> and Cu<Superscript>2+</Superscript>

A novel 1,8-naphthalimide dye with simple structure has been produced by a facile synthetic method for colorimetric and fluorescent sensing of H⁺ and Cu²⁺. In CH₃CN/H₂O (1/1, v/v), the dye could monitor H⁺ using dual channels (ratiometric absorbance and fluorescence intensity change) from pH 6.2 to 12.0. Meanwhile, in the pH range of 1.9–5.2, the dye could also be used to detect Cu²⁺ using triple channels [ultraviolet–visible (UV–Vis) absorption, fluorescence intensity reduction, as well as fluorescence blueshift]. The detection limits for Cu²⁺ evaluated by colorimetric and fluorescent titration were 6.10 × 10^?7 and 2.62 × 10^?7 M, respectively. The dye exhibited specific selectivity and sensitivity for H⁺ and Cu²⁺ over various coexisting metal ions. Moreover, the sensing mechanism of the dye for H⁺ and Cu²⁺ was carefully examined.     

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 Highly Selective Colorimetric and Fluorescent Probe for Cu2+ and Hg2+ Ions Based on a Distyryl BODIPY with Two Bis(1,2,3‐triazole)amino Receptors

A new distyryl boron dipyrromethene (BODIPY) with two bis(1,2,3‐triazole)amino substituents has been prepared by typical Knoevenagel condensation followed by click reaction. The compound selectively binds to Cu²⁺ and Hg²⁺ ions in CH₃CN/H₂O (1:1 v/v) to give remarkably blueshifted electronic absorption and fluorescence bands as a result of inhibition of the intramolecular charge‐transfer process upon binding to these metal ions. The color changes can be easily seen by the naked eye. The binding stoichiometry between this probe and Cu²⁺ ions has been determined to be 1:2 by a Job plot of the fluorescence data with a binding constant of ((6.2±0.6)×10⁹) M ^?2. The corresponding value for Hg²⁺ ions is about sixfold smaller.     

A highly selective fluorescent chemosensor for Fe (III) based on rhodamine 6G dyes derivative

A new fluorescent probe L based on the rhodamine 6G platforms for Fe³⁺ has been designed and synthesised. L showed excellent selectivity and high sensitivity for Fe³⁺ against other metal ions such as K⁺, Na⁺, Ag⁺, Cu²⁺, Co²⁺, Mg²⁺, Cd²⁺, Ni²⁺, Zn²⁺, Fe²⁺, Hg²⁺, Ce³⁺ and Y³⁺ in HEPES buffer (10 mM, pH 7.4)/CH₃CN (40:60, V/V). The distinct color change and the rapid emergence of fluorescence emission provided naked-eyes detection for Fe³⁺. The recognition mechanism of the probe toward Fe³⁺ was evaluated by Job’s plots, IR and ESI-MS. In order to further study their fluorescent properties, L + Fe³⁺ fluorescence lifetime was also measured. Moreover, the test strip results showed that these probes could act as a convenient and efficient Fe³⁺ test kit.     

A Novel Naked-Eye and Dual-Channel Responsive Fluorescent Probe for Cu2+ Based on 3,4-Disubstituted-1,8-naphthalimide

A new 3,4-disubstituted-1,8-naphthalimide derivative H1 was designed and synthesized as a selective fluorescent probe for Cu²⁺ over miscellaneous metal ions in aqueous media. Upon mixing with Cu²⁺ in CH₃OH:H₂O (1:1, volume ratio), the increase of fluorescence intensity and a bathochromic shift of absorbance of H1 could be observed with a notable color response (changing from yellow to pink). Furthermore, Cu²⁺ coordinates to the probe H1 and a 1:1 metal-ligand complex was formed.     

Novel fluorescent probe bearing triarylimidazole and pyridine moieties for the rapid and naked-eye recognition of Cu2+

A new fluorescent probe (TPIP) bearing triarylimidazole and pyridine moieties was synthesized and applied to the detection of Cu²⁺ with high sensitivity and selectivity. Upon the addition of Cu²⁺, the probe displayed an apparent dual-channel signal change of the UV–Vis absorption and fluorescence spectra, and the obvious color change from bright blue to colorless under a UV lamp was discernable to the naked eye. The sensing mechanism of the probe towards Cu²⁺ was verified to be via complexation, and the binding reaction was rapidly complete within 30?s. Good linearity was observed between the probe and Cu²⁺, and the detection limit was calculated to be 1.96?×?10^?8?M. The reversibility of the probe was easily achieved by adding EDTA, which released the free probe with over 95% fluorescence recovery. Furthermore, the recognition of Cu²⁺ on TLC plates was realized, indicating the potential utility of the probe.     

Imidazo[1,2-a]pyridine-substituted coumarin as a selective ratiometric sensor for Cu2+ ion

A novel fluorescent chemosensor, (E)-7-(diethylamino)-3-((2-phenylimidazo[1,2-a]pyridin-3-ylimino)methyl)-2H-chromen-2-one 1a, has been synthesised and characterised. This chemosensor displayed an extreme selective fluorescence emission only with Cu²⁺ ion over all other metal ions examined. The Job’s plot experiment analysis suggested the binding ratio of the chemosensor 1a with Cu²⁺ was 1:1 metal-to-ligand ratio. The association constant for Cu²⁺ towards receptor 1a obtained from Benesi–Hildebrand plot was found to be 4.859 × 10³ M^?1 with a detection limit 4.6 × 10^?8 M. Fluorescence enhancement caused by Cu²⁺ binding with chemosensor 1a attributed to combinational effect of intramolecular charge transfer and chelation-enhanced fluorescence occurred at pH 8.0.     

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.     

Simultaneous determination of Hg(II) and Cu(II) in water samples using fluorescence quenching sensor of N-doped and N,K co-doped graphene quantum dots

The present study was aimed to use of N doped graphene quantum dots (N-GQDs) and N,K co-doped graphene quantum dots (N,K-GQDs) as a fluorescence quenching sensor to determine both mercury and copper in water sample, simultaneously using simple fluorescence protocol. Each of N-GQDs or N,K-GQDs was optimized separately with 1–5% (w/v) HNO₃ or KNO₃, respectively, and their quantum yields were determined and compared. It was found that N-GQDs, obtained from 3% (w/v) HNO₃ doped resulted higher fluorescence intensity at the maximum excitation and emission wavelengths of 370 and 460 nm, respectively, with higher quantum yield (QY = 83.42%) compared with that of undoped GQDs (QY = 16.35%). While N,K-GQDs obtained from 5%(w/v) KNO₃ gave somewhat different fluorescence spectrum, but still had the same maximum excitation and emission wavelengths with rather highest QY (94.07%). However, it is interesting that detection sensitivity expressed as slope of their calibration curve (y = 5.43x − 19.48; r² = 0.9971) of the N-GQDs is rather higher than that (y = 1.29x + 17.66; r² = 0.9977) of the N,K-GQDs for Hg²⁺ fluorescence quenching sensor, and the fluorescence intensity of N-GQDs had better selectively quenching effect only by both Hg²⁺ and Cu²⁺. Thus, their quenching effects were selected to develop the fluorescence turn-off sensor for trace level of both metal ions in real water samples. For method validation, the N-GQDs exhibited high sensitivity to detect both Hg²⁺ and Cu²⁺ with wide linear ranges of 20–100 μM and 100–500 μM, respectively. Limit of detection (LOD) and limit of quantitation (LOQ) were 0.42 μM & 1.41 μM for Hg²⁺ and 13.19 μM & 43.97 μM for Cu²⁺, respectively, with their precision expressed as an intra-day and an inter-day analysis of 6.98% & 11.35% for Hg²⁺ and 11.78% & 9.43% for Cu²⁺, respectively. Also the study of matrix analysis of the water samples (drinking water and tap water), was carried out using N-GQDs and N,K-GQDs resulted good percentage recoveries in comparison with those using undoped GQDs under the same optimum conditions.     

New lower rim looped calix[4]arene for ratiometric and chromogenic recognition of Cu2+

A new calix[4]arene derivative in its cone conformation and bearing Schiff base loop at the lower rim has been synthesized and evaluated as a specific molecular probe for copper ions. The new molecular receptor 4 shows a selective visible change in color from colorless to yellow only in the presence of Cu²⁺ ions which was confirmed by a significant bathochromic shift (?λ_max = 76 nm) in its absorption spectrum. The stoichiometry of the copper complex was calculated to be 1:1. These results may help to design more efficient chemical sensors for determining copper in biological systems.     

Cu nanoclusters-based ratiometric fluorescence probe for ratiometric and visualization detection of copper ions

Copper is a highly toxic environmental pollutant with bioaccumulative properties. Therefore, sensitive detection of Cu²⁺ is very important to prevent over-ingestion, and visual detection is preferred for practical applications. In this work, we developed a simple and environmental friendly approach to synthesize hyperbranched polyethyleneimine-protected copper nanoclusters (hPEI-Cu NCs) with great stability against extreme pH, high ionic strength, thiols etching and light illumination, which were then conjugated to the surface of silica coated CdSe quantum dots (QDs) to design a ratiometric fluorescence probe. In the presence of different amounts of Cu²⁺ ions, the fluorescence of Cu NCs can be drastically quenched, while the emission from QDs stayed constant to serve as a reference signal and the color of the probe changed from yellow-green to red, resulting in ratiometric and visualization detection of Cu²⁺ ion with high accuracy. The detection limit for Cu²⁺ was estimated to be 8.9 nM, much lower than the allowable level of Cu²⁺ in drinking water (∼20 μM) set by U.S. Environmental Protection Agency. Additionally, this probe can be also applied for the determination of Cu²⁺ ion in complex real water samples.     

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.     

Determination of Trace Copper by Fluorescence Spectrophotometry Based on Cu(DP)2+ and Cu‐4.0‐Generations Polyamidoamine Dendrimers Catalyze Cu2+ to Oxidize Fluorescein

Abstract

Fluorescein can emit strong and stable fluorescence. Cu²⁺ can oxidize fluorescein, which causes the fluorescence signal to diminish. Cu(DP)²⁺ (DP refers to α,α′‐dipyridyl) and Cu‐GPD‐4.0 (GPD‐4.0 refers to 4.0‐generations polyamidoamine dendrimers) both can catalyze Cu²⁺ to oxidize fluorescein, which causes the fluorescence signal to diminish sharply. The ΔF is directly proportional to the content of copper. Based on the facts above, a new catalytic fluorescence spectrophotometry for the determination of trace copper using Cu(DP)²⁺ and Cu‐GPD‐4.0 was established. The linear range of this method is 0.040–28 pg mL^?1. The regression equation for working curve is ΔF=209.5+14.39 C_Cu ²⁺ (pg mL^?1), n=7; correlation coefficient is 0.991. The detection limit of this method is 1.0×10^?14 g mL^?1. After replicate measurement times, RSDs are 3.1% and 4.2% for samples containing 0.040 and 28 pg mL^?1 Cu²⁺, respectively. This method is rapid and precise with high sensitivity and good repeatability. The method has been applied to the determination of trace copper in tea and human hair with satisfactory results. Meanwhile, the mechanism for the determination of trace copper by catalytic fluorescence spectrophotometry using Cu(DP)²⁺ and Cu‐GPD‐4.0 was also discussed.     

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.     

Novel naphthalene-based fluorescent chemosensors for Cu2+ and Fe3+ in aqueous media

Three novel compounds bearing 2,7-dihydroxylnaphthalene capable of detecting Cu²⁺ or Fe³⁺ have been synthesised based on photoinduced electron transfer. The ability of these compounds for complex transition metal ions has been studied, and complex stoichiometry for Cu²⁺ and Fe³⁺ complex has been determined in the Tris–HCl (0.01 M DMSO/H₂O (v/v) 1:1, buffer, pH 7.4) solution system by fluorescence titration experiments. These chemosensors form a 1:1 complex with Cu²⁺ or Fe³⁺ and show a fluorescent quenching with a binding constant of (4.46 ± 0.29) × 10³ and (8.04 ± 0.26) × 10⁴, respectively.