A minimal core based fluorophore for selective detection of Zn(II) ions in aqueous solution and living cells

A minimal core based fluorophore was introduced as a selectively fluorescent "turn on" sensor for Zn(2+) ions in aqueous solution. Addition of Zn(2+) ions to the fluorophore generates a significant emission through a 1:1 ligand-to-metal complex. The fluorescence titration experiment of the minimal core based fluorophore with various metal ions shows that the pyromellitic diimide derivative also has the advantage of a high selectivity to Zn(2+) ions over other metals such as Ni(2+), or Co(2+), Cu(2+), Fe(3+), Fe(2+). More than 8 fold increase in the intensity of fluorescence was observed for the Zn(2+)-bound fluorophore compared to Zn-free fluorophore. Due to its small molecular size, the fluorophore was cell-permeable and successfully applied to the detection of Zn(2+) in living cells. With its relatively high sensitivity to Zn(2+) in living cells, the synthesized new fluorophore will be very useful in the studies on various biological functions of Zn(2+).     

Selective recognition iodide in aqueous solution based on fluorescence enhancement chemosensor

A novel and simple fluorescence enhancement method for selectively sensing iodide was proposed based on metal complex formation between mercuric(II) ion with fluorophore (p-((dimethylamino)benzylidene)thiosemicarbazide, 1) and with anion in aqueous solution. The 1-Hg complex was found to show selectively and sensitively fluorescence enhancement response toward iodide over than S(2-), EDTA, SCN-, CH(3)CO(2-), Br-, Cl-, F-, H2PO4- and SO4(2-), which was attributed to the higher stability of inorganic complex between iodide and mercuric(II).     

A fluorescent chemosensor for Hg based on naphthalimide derivative by fluorescence enhancement in aqueous solution

Naphthalimide derivative (compound 1) containing hydrophilic hexanoic acid group was synthesized and used to recognize Hg²⁺ in aqueous solution. The fluorescence enhancement of 1 is attributed to the formation of a complex between 1 and Hg²⁺ by 1:1 complex ratio (K = 2.08 × 10⁵), which has been utilized as the basis of fabrication of the Hg²⁺-sensitive fluorescent chemosensor. The comparison of this method with some other fluorescence methods for the determination of Hg²⁺ indicated that the method can be applied in aqueous solution rather than organic solution. The analytical performance characteristics of the proposed Hg²⁺-sensitive chemosensor were investigated. The chemosensor can be applied to the quantification of Hg²⁺ with a linear range covering from 2.57 × 10⁻⁷ to 9.27 × 10⁻⁵ M and a detection limit of 4.93 × 10⁻⁸ M. The experiment results show that the response behavior of 1 toward Hg²⁺ is pH independent in medium condition (pH 4.0–8.0). Most importantly, the fluorescence changes of the chemosensor are remarkably specific for Hg²⁺ in the presence of other metal ions, which meet the selective requirements for practical application. Moreover, the response of the chemosensor toward Hg²⁺ is fast (response time less than 1 min). In addition, the chemosensor has been used for determination of Hg²⁺ in hair samples with satisfactory results, which further demonstrates its value of practical applications.     

Highly selective and sensitive near-infrared fluorescent sensors for cadmium in aqueous solution

On the basis of tricabocyanine, two near-infrared fluorescent sensors CYP-1 and CYP-2 have been designed and synthesized. Both of them can selectively and sensitively recognize Cd(2+) from other metal ions, especially the CYP-2, which can distinguish Cd(2+) in neutral buffer solution.     

A novel water-soluble AIE-based fluorescence probe with red emission for the sensitive detection of heparin in aqueous solution and human serum samples

Heparin is widely used to anticoagulation treatment in clinic, while the overdoses of heparin can cause potentially catastrophic complications. Thus, the selective and sensitive detection of heparin is of great importance. Herein, a novel water-soluble AIE-based fluorescent probe (TIBI) with red emission (650 nm) has been rationally developed to detect heparin by the electrostatic-interaction and ion replacing strategy. TIBI exhibited excellent selectivity and low detection limit (0.08 μM) for detection of heparin. Moreover, TIBI was successfully applied to detect heparin in complicated serum samples with satisfactory results. This study holds great promise for real time monitoring heparin in clinical application.     

Absorption and fluorescence of a nonionic detergent in aqueous solution

The absorption and fluorescence spectra of a detergent, polyoxyethylene octylphenyl ether, were measured in water at different concentrations. The absorption spectra had a peak at 275 mμ and a shoulder at 281 mμ. The spectra were independent of concentration below the critical micelle concentration, but the molar extinction coefficients of the peak and the shoulder increased with concentration above the critical micelle concentration. The critical micelle concentration value derived from the absorption data was in good agreement with those obtained by other methods. The fluorescence spectra of the detergent in water were independent of concentration in dilute solutions, if the intensities of the spectra were normalized at the peak at 302 mμ. At higher concentrations, a weak excimer band appeared at 345 mμ, whose intensity increased with concentration. The excimer band manifested itself at a concentration slightly lower than the critical micelle concentration. The main band decreased and the excimer band increased, as the temperature was raised. An excimer band was observed in the same region of the spectra for the pure detergent, either in the solid or liquid state. The equilibrium solid spectra exhibited a very strong excimer emission. It was concluded that the excimers were formed within micelles in the case of aqueous solutions.     

A near-infrared fluorescent sensor for detection of cyanide in aqueous solution and its application for bioimaging

A new NIR fluorescent sensor based on an amine-substituted heptamethine cyanine dye displayed a highly selective fluorescence enhancement with cyanide in aqueous solutions, and was applied for the imaging of anthropogenic and biogenic cyanide.     

A turn-on and reversible fluorescence sensor with high affinity to Zn in aqueous solution

A new simple receptor 1 based on aminosalicylimine was prepared. It exhibited an ‘off–on fluorescence type’ mode with high sensitivity in the presence of Zn²⁺. In particular, this chemosensor could clearly distinguish Zn²⁺ from Cd²⁺. Also, it could be a reusable chemosensor because the addition of EDTA quenched the fluorescence of the Zn²⁺-2·1 complex. Furthermore, receptor 1 had a sufficiently low detection limit (68 nM) in aqueous solutions, which implies that 1 could sense the nanomolar concentration of Zn²⁺. Therefore, this sensor has the ability to be a practical system for the monitoring of Zn²⁺ concentrations in aqueous samples.     

Water-induced fluorescence quenching of aniline and its derivatives in aqueous solution

Nonradiative deactivation processes of excited aniline and its derivatives in aqueous solution were investigated by steady-state and time-resolved fluorescence measurements to reveal characteristic solvent effects of water on the relaxation processes of excited organic molecules. The magnitude of nonradiative rate (k_nr) of excited aniline derivatives increased significantly in water compared to that in organic solvents (cyclohexane, ethanol, and acetonitrile). The fluorescence lifetime measurements in organic solvent/H₂O mixed solvents suggested that the fluorescence quenching in water was not due to exciplex formation but due to interactions with a water cluster. From temperature effect experiments on the fluorescence lifetime and quantum yield of aniline, N-methylaniline, and N,N-dimethylaniline, the apparent activation energies for the nonradiative deactivation rate in water were determined as 21, 30, and 41 kJ mol^-1, respectively. Upon substitution of hydrogen atoms in the aromatic ring of aniline derivatives for deuterium atoms resulted in normal deuterium isotope effect in cyclohexane, i.e. k_nr decreased by deuterium substitution, while in water the same deuterium substitution led to an increase in k_nr (the inverse isotope effect). The inverse isotope effects implied that a direct internal conversion to vibrationally higher excited states in the electronically ground state is not a dominant mechanism but the transition to a close-lying energy level, e.g. the relaxation to charge transfer to solvent (ctts) state, would be associated with the quenching mechanism in water.     

A fluorescence "turn-on" chemodosimeter for Cu2+ in aqueous solution based on the ion promoted oxidation

We developed a novel method for Cu(2+) detection based on the ion promoted oxidation reaction. Chemodosimeter L (weak fluorescence) can be oxidized into 3-benzothiazoly-7-N,N-diethylaminocoumarin (strong green fluorescence, coumarin 6) by Cu(2+) with high selectivity and sensitivity in HEPES (10 mM, pH = 7.4) buffer containing 50% (v/v) water-CH(3)CN solution.     

A highly selective and ratiometric fluorescence probe for the detection of Hg and pH change based on coumarin in aqueous solution

A simple but highly selective coumarin-based fluorescence probe 1, 8-(1,3-dithiane)-7-hydroxycoumarin was designed and synthesized for both the ratiometric detection of Hg²⁺ and the on–off response to pH change in aqueous solution. The sensor detected Hg²⁺ selectively via Hg²⁺-promoted thioacetal deprotection reaction within five minutes and reflected pH in the range from 7.8 to 11.9 as a result of the equilibrium between weak-fluorescent acid form and strong-fluorescent base form. In addition, the probe has an excellent selectivity towards Hg²⁺ over other competitive metal ions for biomedical and environmental applications. The sensing behavior of our probe was studied by UV–visible absorption spectra and fluorescence spectra.     

A new turn-on fluorescence probe for Zn in aqueous solution and imaging application in living cells

We designed and synthesized a new pyrazoline-based turn-on fluorescence probe for Zn²⁺ by the reaction of chalcone and thiosemicarbazide. The structure of the probe was characterized by IR, NMR and HRMS spectroscopy. The probe (L) exhibits high selectivity and sensitivity for detecting Zn²⁺ in buffered EtOH/HEPES solution (EtOH/HEPES = 1/1, pH 7.2) with 80-fold fluorescence enhancement, which is superior to previous reports. Job’s plot analysis revealed 1:1 stoichiometry between probe L and Zn²⁺ ions. The association constant estimated by the Benesi–Hildebrand method and the detection limit were 3.92 × 10³ M⁻¹ and 5.2 × 10⁻⁷ M, respectively. A proposed binding mode was confirmed by ¹H NMR titration experiments and density functional theory (DFT) calculations. The probe is cell-permeable and stable at the physiological pH range in biological systems. Because of its fast response to Zn²⁺, the probe can monitor Zn²⁺ in living cells. Moreover, the selective binding of L and Zn²⁺ was reversible with the addition of EDTA in buffered EtOH/HEPES solution and Zn²⁺ could be imaged in SH-SY5Y neuron cells.     

Synthesis and fluorescence behaviour of crown and azacrown ethers carrying the dansyl fluorophore as a pendant in acetonitrile solution

The influence of Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Pb²⁺ and Al³⁺ ions on the spectroscopic properties of the dansyl group covalently linked to crown ether or diazacrown ethers was investigated by means of absorption and emission spectrophotometry. Interaction of the alkali metal ions with all fluoroionophores studied is weak, while alkaline earth metal ions interact strongly causing about 50% quenching of dansyl fluorescence of A21C5-Dns and A₂18C6-Dns. The Cu²⁺, Pb²⁺ and Al³⁺ cations interact very strongly with dansyl chromophore regardless the crown ether type, causing a major change in absorption spectrum of the chromophore and forming non-fluorescent complexes. The Co²⁺, Ni²⁺, Zn², Mg²⁺ and Ag⁺ cations interact moderately with all fluoroionophores studied causing about 20% of fluorescence quenching of dansyl, except for a strong dansyl fluorescence quenching of 15C5-Dns by Co²⁺ ion. The quenching efficiency of didansylated fluoroionophores by the alkali metal ions and alkaline earth metal ions is weaker than monodansylated ones.     

Difluoroboron β-diketonate dye with intense red/near-infrared fluorescence in solutions and solid states

We reported a difluoroboron β-diketonate dye that displays bright red/NIR fluorescence in both solutions and solid states.     

Time-resolved polarization measurements of porphyrin fluorescence in solution and in single cells

Porphyrin monomers, dimers and aggregates, which can be differentiated on the basis of their fluorescence lifetimes, are shown to possess different degrees of fluorescence polarization. This opens up new possibilities for microscopic imaging of these individual components in photosensitization and tumour detection. A rough estimate of the size of the porphyrin aggregates is obtained from the data of time-resolved fluorescence anisotropy.     

A highly selective fluorescence chemosensor for Pb(II) in neutral buffer aqueous solution

A 3,4-dimethylthieno[2,3-b]thiophene-based fluorogenic probe bearing benzo[d]-thiazole-2-thio unit (sodium 3,4-bis ((benzo[d]thiazol-2-ylthio)methyl) thieno [2, 3-b]thio-phene-2, 5-dicarboxylate) was developed as a novel fluorescent chemosensor with high selectivity towards Pb(II) over other cations tested. The new probe exhibited good water solubility and only sensed Pb(II) among metal ions examined in neutral 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer solution. The selectivity and sensitivity of fluorogenic probe to Pb(II) were discussed on the basis of experimental results.     

Formation of ternary poly(acrylic acid)-surfactant-Cu2+ complexes in aqueous solution: quenching of pyrene fluorescence and pH-controlled "on-off" emitting properties

The formation of binary and ternary complexes of poly(acrylic acid) (PAA) with N, N, N, N-dodecyltrimethylammonium chloride (DTAC) and/or Cu (2+) ions is investigated in dilute aqueous solution through turbidimetry, viscometry, and pyrene fluorescence probing. It is shown that the PAA-DTAC and PAA-Cu (2+) complexation as well as the formation of ternary PAA-DTAC-Cu (2+) complexes are controlled from the pH of the aqueous solution. A pronounced quenching of the emission of pyrene is observed when ternary PAA-DTAC-Cu (2+) complexes are formed, as a result of the close proximity of Cu (2+) ions (complexed along the polymer chain) and the probe (solubilized in the hydrophobic mixed polymer-surfactant aggregates), as indicated from the corresponding Stern-Volmer plots. A significant quenching is also observed when poly(sodium styrene sulfonate) is used instead of PAA, indicating that electrostatically bound Cu (2+) ions are still effective quenchers of the emission of the probes under similar conditions. Finally, it is demonstrated that the formation-deformation of the ternary PAA-DTAC-Cu (2+) complexes upon changing pH may act as a pH-controlled "on-off" switch of the emission of pyrene in aqueous solution.     

A fluorescence turn-on probe for the detection of thiol-containing amino acids in aqueous solution and bioimaging in cells

A turn-on fluorescent probe, based on a water-soluble terphenyl derivative, for the detection of cysteine and homocysteine is reported. The aldehyde groups in the probe play crucial roles in providing reaction with thiol groups in the amino acids, leading to a formation of thiazolidine (from cysteine) or thiazinane ring (from homocysteine). As a result, the new formation of such rings alters the electronic property of the conjugated system in the probe and results in emission enhancement. The probe in aqueous solution exhibits a remarkable increase in its quantum yield upon exposure to cysteine (up to 20-fold) and to homocysteine (up to 700-fold), while slight quenching is observed in the presence of glutathione. Moreover, an investigation on time-resolved fluorescence spectra of the probe in the presence of cysteine and homocysteine reveals potential discriminatory detection of cysteine and homocysteine. Bioimaging of the thiols in live HeLa cells was successfully applied.