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.     

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⁺.     

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.     

Highly selective chromogenic and fluorogenic probe based on benzothiazole-thiosemicarbazone Schiff base for detection of copper (II) in real samples

Copper is the third most abundant essential transition metal ion in the human body. It's responsible for important activities in many living things, but excessive intake of Cu²⁺ can lead to a range of diseases. A colorimetric and turn-off fluorescent probe (E)-2-(5-(benzothiazol-2-yl)-2-(diethylamino)-4-hydroxybenzylidene)-N-phenylhydrazine-1-carbothioamide ( ZTR ) was designed and synthesized by thiosemicarbazone Schiff base as a specific complexes site strategy to achieve highly specific Cu²⁺ detection. The fluorescence of the probe ZTR solution fell dramatically when Cu²⁺ was added, and its appearance changed from dazzling blue to nearly colorless. The simple structure and readily available fluorescent probe provide a novel approach for the quantitative detection of Cu²⁺ in the linear range from 0 to 0.12 μM, with a detection limit down to 16 nM, and with high selectivity for Cu²⁺ over 15 other metal ions. Job’s plot analysis showed that probe ZTR and Cu²⁺ formed a 1:1 coordination complex. In addition, because of its low detection limits and fast response time, the created fluorescent molecule was effectively used to study the target ions on test paper strips and in water samples.))     

Development of an oxidative dehydrogenation-based fluorescent probe for Cu and its biological imaging in living cells

Based on a boron dipyrromethene (BODIPY) derivative containing an N, O and S tridentate ligand, a Cu²⁺ fluorescent probe BTCu was developed. The detection mechanism was verified as Cu²⁺-promoted oxidative dehydrogenation of an amine moiety, leading to a formation of a fluorescent Cu⁺-Schiff base complex. Free BTCu exhibited a maximum absorption wavelength at 496 nm, and a very weak maximum emission at 511 nm. Upon addition of various metals ions, it showed large fluorescence enhancement toward Cu²⁺ (417-fold in MeCN and 103-fold in MeCN/HEPES solution, respectively) with high selectivity. The detection limits are as low as 1.74 × 10⁻⁸ M and 4.96 × 10⁻⁸ M in the two different solutions, respectively. And BTCu could work in a wide pH range with an extraordinary low pK_a of 1.21 ± 0.06. Using fluorescence microscopy, the probe was shown to be capable of penetrating into living cells and imaging intracellular Cu²⁺ changes.     

A new colorimetric and fluorescent bifunctional probe for Cu and F ions based on perylene bisimide derivatives

A perylene bisimide derivative (PBI) based colorimetric and fluorescent bifunctional probe PAM-PBI was designed and synthesized. It was highly selective and sensitive for distinguishing both Cu²⁺ and F⁻ from other ions through a conspicuous change of UV–vis and fluorescence spectra. The recognition of Cu²⁺ by PAM-PBI showed an obvious color change from rose red to purple in aqueous solution, while the sensing of F⁻ gave a marked color change from rose red to light green in THF.     

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).     

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.     

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.     

Characterization of a Hg2+-Selective Fluorescent Probe Based on Rhodamine B and Its Imaging in Living Cells

A small organic molecule P was synthesized and characterized as a fluorometric and colorimetric dual-modal probe for Hg²⁺. The sensing characteristics of the proposed probe for Hg²⁺ were studied in detail. A fluorescent enhancing property at 583 nm (>30 fold) accompanied with a visible colorimetric change, from colorless to pink, was observed with the addition of Hg²⁺ to P in an ethanol-water solution (8:2, v/v, 20 mM HEPES, pH 7.0), which would be helpful to fabricate Hg²⁺-selective probes with “naked-eye” and fluorescent detection. Meanwhile, cellular experimental results demonstrated its low cytotoxicity and good biocompatibility, and the application of P for imaging of Hg²⁺ in living cells was satisfactory.     

A highly sensitive and selective fluorescent probe for Fe3+ containing two rhodamine B and thiocarbonyl moieties and its application to live cell imaging

A novel turn-on rhodamine B-based fluorescent chemosensor (RBCS) was designed and synthesized by reacting N-(rhodamine B)lactam-1,2-ethylenediamine and carbon disulfide. Upon addition of Fe³⁺ in EtOH/H₂O solution (2:1, v/v, HEPES buffer, 0.6?mM, pH 7.20), the RBCS displayed a significant fluorescence enhancement at 582?nm and a dramatic color change from colorless to pink, which can be detected by the naked eye. Significantly, the RBCS exhibited a highly selective and sensitive ability toward Fe³⁺. The detection limit of the probe was 2.05?×?10^?7?M. Job's plot indicated the formation of 1:1 complex between the RBCS and Fe³⁺. Moreover, the practical use of the RBCS is demonstrated by its application in the detection of Fe³⁺ in HeLa cells.     

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)).     

Ratiometric and turn-on monitoring for heavy and transition metal ions in aqueous solution with a fluorescent peptide sensor

A novel fluorescent peptide sensor containing tryptophan (donor) and dansyl fluorophore (acceptor) was synthesized for monitoring heavy and transition metal (HTM) ions on the basis of metal ion binding motif (Cys-X-X-X-Cys). The peptide probe successfully exhibited a turn on and ratiometric response for several heavy metal ions such as Hg²⁺, Cd²⁺, Pb²⁺, Zn²⁺, and Ag⁺ in aqueous solution. The enhancements of emission intensity were achieved in the presence of the HTM ions by fluorescent resonance energy transfer (FRET) and chelation enhanced fluorescence (CHEF) effects. The detection limits of the sensor for Cd²⁺, Pb²⁺, Zn²⁺, and Ag⁺ were lower than the EPA's drinking water maximum contaminant levels (MCL). We described the fluorescent enhancement, binding affinity, and detection limit of the peptide probe for HTM ions.     

A Coumarin-boronic Based Fluorescent “ON-OFF” Probe for Hg2+ in Aqueous Solution

In this work, we reported a simple coumarin-boronic acid ester fluorescent probe 1 , which displayed very high “ON-OFF” fluorescence response for Hg²⁺ in an aqueous environment (H₂O/CH₃CN = 1:1, v/v) or in a PBS solution (pH = 7.4). With the addition of Hg²⁺ to the solution of probe, a color change from light yellow to orange could be observed by naked eye. The detection limits were lower than the permitted level of Hg²⁺ in drinking water defined by WHO. Infrared spectroscopy, mass spectroscopy and ¹H NMR titration studies showed that probe 1 formed a 1:1 complex with Hg²⁺. In addition, the probe was non-toxic to cells and could stain specifically the membrane region surrounding the HeLa cell.     

Facile Synthesis of Aminated Graphene Quantum Dots for Promising and Selective Detection of Cobalt and Copper Ions in Aqueous Media

Due to the rapid development of industrialization, various environmental problems such as water resource pollution are gradually emerging, among which heavy metal pollution is harmful to both human beings and the environment. As a result, there are many metal ion detection methods, among which fluorescence detection stands out because of its rapid, sensitive, low cost and non-toxic characteristics. In recent years, graphene quantum dots have been widely used and studied due to their excellent properties such as high stability, low toxicity and water solubility, and have a broad prospect in the field of metal ion detection. A novel high fluorescence Cu²⁺, Co²⁺ sensing probe produced by graphene quantum hydrothermal treatment is reported. After heat treatment with hydrazine hydrate, the small-molecule precursor nitronaphthalene synthesized by self-nitrification was transformed from blue fluorescent GQDs to green fluorescent amino-functionalized N–GQDs. Compared with other metal ions, N–GQDs are more sensitive to Cu²⁺ and Co²⁺ on the surface, and N–GQDs have much higher selectivity to Cu²⁺ and Co²⁺ than GQDs. The strategy proposed here is simple and economical in design.     

A colorimetric and fluorescent sensor for sequential detection of copper ion and cyanide

A simple cation sensor 1 ((E)-9-((2-hydroxynaphthalen-1-ylimino)methyl)-1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinolin-8-ol) bearing both a julolidine moiety and a naphthol moiety was designed and synthesized as a colorimetric sensor for Cu²⁺. In methanol solution of 1, the presence of Cu²⁺ led to a distinct naked-eye color change from yellow to purple. The proposed sensing mechanism might be attributed to the decrease in internal charge transfer band. Moreover, the resulting 1–Cu²⁺ complex sensed cyanide in a fluorometric way via fluorescent changes. These results demonstrate a novel type of the sequential recognition of Cu²⁺ and CN⁻ using two different sensing methods, color change, and fluorescence.     

A Highly Selective Chemosensor for Cu2+ Based on a Diarylethene Linking an Aminoquinoline Unit

A new diarylethene derivative containing an aminoquinoline unit was synthesized and its structure was determined by single crystal X‐ray diffraction analysis. Its properties such as photochromism, fluorescent switches and detection for metal ions were measured. The results indicated that the closed‐ring of the diarylethene was highly selective toward Cu²⁺ with an obvious absorption decrease and color changes from blue to colorless, even in the presence of other metal ions. The binding constant for the closed isomer of this new diarylethene and Cu²⁺ was 2.0×10⁴ L·mol^?1 and the limit of detection for Cu²⁺ was calculated to be lower than that in drink water. Finally, a logic circuit was constructed by using the absorption intensity as the output signal with the inputs of the combinational stimuli of light and Cu²⁺.     

Solvent-dependent chromogenic sensing for Cu and fluorogenic sensing for Zn and Al: a multifunctional chemosensor with dual-mode

A new multifunctional chemosensor 1 was synthesized and characterized by spectroscopic tools along with a single crystal X-ray crystallography. It can exhibit selective recognition responses toward Cu²⁺, Zn²⁺ and Al³⁺ in different solvent systems with bimodal methods (colorimetric and fluorescence). This sensor 1 detected Cu²⁺ ions through a distinct color change from colorless to yellow in aqueous solution. Interestingly, the receptor 1 was found to be reversible by EDTA. The detection limit (11 μM) of 1 for Cu²⁺ is much lower than WHO guideline (30 μM) in drinking water. In addition, the sensor 1 showed significant fluorescence enhancements in the presence of Zn²⁺ ion and Al³⁺ ion in two different organic solvents (DMF and MeCN), respectively. The binding modes of the three complexes were determined to be a 1:1 complexation stoichiometry through Job plot, ESI-mass spectrometry analysis, and ¹H NMR titration.     

Phenanthroline-fluorescein molecular hybrid as a ratiometric and selective fluorescent chemosensor for Cu2+ via FRET strategy: synthesis,computational studies and in vitro applications

A FRET-based chemosensor L containing donor phenanthroline and acceptor fluorescein moiety was designed, synthesised and characterised for the ratiometric fluorescent detection of Cu²⁺ in organo-aqueous solution. Probe L showed high selectivity and excellent sensitivity towards Cu²⁺ ions by exhibiting both colorimetric and fluorometric changes due to opening of the spirolactum ring of fluorescein upon complexation with Cu²⁺. In presence of Cu²⁺ ions, probe L formed L-Cu²⁺ complex in 1:1 stoichiometric fashion which is established on the basis of Job’s plot and mass spectroscopy. We also performed DFT computational studies to know the binding nature and coordination feature of the complex. Furthermore, fluorescence imaging studies revealed that probe L was cell permeable and could be used to detect intracellular Cu²⁺ in living cells.     

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.