A fluorescent chemosensor for cobalt ions based on a multi-substituted phenol-ruthenium(II) tris(bipyridine) complex

An amide-linked 2,6-bis{[(2-hydroxy-5-tert-butylbenzyl)(pyridyl-2-methyl)-amino]-methyl}-4-methylphenol-ruthenium(II) tris(bipyridine) 2PF₆⁻ complex, 1, was first used to recognize Co(II) in EtOH/H₂O (1:1, v/v) solution, with the ruthenium(II) tris(bipyridine) moiety selected as a fluorophore and the multi-substituted phenol unit chosen as a receptor. The fluorescence quenching of 1 was attributed to the formation of an inclusion complex between multi-substituted phenol unit and Co(II) by 1:1 complex ratio (K = 2.5 × 10⁵), which has been utilized as the basis of the fabrication of the Co(II)-sensitive fluorescent chemosensor. The analytical performance characteristics of the proposed Co(II)-sensitive chemosensor were investigated. The sensor can be applied to the quantification of Co(II) with a linear range covering from 1.0 × 10⁻⁷ to 5.0 × 10⁻⁵ M and a detection limit of 5 × 10⁻⁸ M. The experiment results show that the response behavior of 1 to Co(II) is pH-independent in medium condition (pH 4.5–9.5) and show excellent selectivity for Co(II) over transition metal cations except Cu(II). The chemosensor has been used for determination of Co(II) in water samples.     

A porphyrin derivative containing 2-(oxymethyl)pyridine units showing unexpected ratiometric fluorescent recognition of Zn2+ with high selectivity

A porphyrin derivative (1), containing two 2-(oxymethyl)pyridine units has been designed and synthesized as chemosensor for recognition of metal ions. Unlike many common porphyrin derivatives that show response to different heavy metal ions, compound 1 exhibits unexpected ratiometric fluorescence response to Zn²⁺ with high selectivity. The response of the novel chemosensor to zinc was based on the porphyrin metallation with cooperating effect of 2-(oxymethyl)pyridine units. The change of fluorescence of 1 was attributed to the formation of an inclusion complex between porphyrin ring and Zn²⁺ by 1:1 complex ratio (K = 1.04 × 10⁵), which has been utilized as the basis of the fabrication of the Zn²⁺-sensitive fluorescent chemosensor. The analytical performance characteristics of the proposed Zn²⁺-sensitive chemosensor were investigated. The sensor can be applied to the quantification of Zn²⁺ with a linear range covering from 3.2 × 10⁻⁷ to 1.8 × 10⁻⁴ M and a detection limit of 5.5 × 10⁻⁸ M. The experiment results show that the response behavior of 1 to Zn²⁺ is pH-independent in medium condition (pH 4.0-8.0) and show excellent selectivity for Zn²⁺ over transition metal cations.     

A new fluorescent chemosensor for anion based on an artificial cyclic tetrapeptide

A cyclic tetrapeptide composed of alternating glycine and 8-amino-4-iso-butoxyquinoline-2-carboxylic acid was designed and synthesized. Its complexation properties with anions were performed by fluorescence spectroscopy and ¹H NMR method.     

A highly selective turn-on fluorescent chemosensor for copper(II) ion

A new pyrene derivative (1) containing a diaminomaleonitrile moiety exhibits high selectivity for Cu²⁺ detection. Significant fluorescence enhancement was observed with chemosensor 1 in the presence of Cu²⁺. However, the metal ions Ag⁺, Ca²⁺, Cd²⁺, Co²⁺, Fe²⁺, Fe³⁺, Hg²⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺ produced only minor changes in fluorescence values for the system. The apparent association constant (K_a) of Cu²⁺ binding in chemosensor 1 was found to be 5.55×10³ M⁻¹. The maximum fluorescence enhancement caused by Cu²⁺ binding in chemosensor 1 was observed over the pH range 5-7.5.     

Highly selectively monitoring heavy and transition metal ions by a fluorescent sensor based on dipeptide

Fluorescent sensor (DMH) based on dipeptide was efficiently synthesized in solid phase synthesis. The dipeptide sensor shows sensitive response to Ag(I), Hg(II), and Cu(II) among 14 metal ions in 100% aqueous solution. The fluorescent sensor differentiates three heavy metal ions by response type; turn on response to Ag(I), ratiometric response to Hg(II), and turn off detection of Cu(II). The detection limits of the sensor for Ag(I) and Cu(II) were much lower than the EPA's drinking water maximum contaminant levels (MCL). Specially, DMH penetrated live cells and detected intracellular Ag⁺ by turn on response. We described the fluorescent change, binding affinity, detection limit for the metal ions. The study of a heavy metal-responsive sensor based on dipeptide demonstrates its potential utility in the environment field.     

A ratiometric fluorescent chemosensor, 1,10-phenanthroline-4,7-dione, for anions in aqueous-organic media

A new fluorescent chemosensor, 1,10-phenanthroline-4,7-dione (1), which is capable of the ratiometric sensing of anions in aqueous MeCN, was developed. Chemosensor 1 recognized an anion via two NH groups in the molecule, and showed a much higher affinity for F⁻ than that of 4-quinolone, which binds to an anion at one NH group of the molecule. Upon binding to F⁻, the intensity of the emission band ascribed to the complex of 1-F⁻ was drastically enhanced, while the emission intensity of unbound 1 gradually decreased. The changes in these two emission bands enabled the successful ratiometric sensing.     

Exploiting the deprotonation mechanism for the design of ratiometric and colorimetric Zn fluorescent chemosensor with a large red-shift in emission

The design, synthesis, and photophysical evaluation of a new naphthalimide-based fluorescent chemosensor, N-butyl-4-[di-(2-picolyl)amino]-5-(2-picolyl)amino-1,8-naphthalimide (1), were described for the detection of Zn²⁺ in aqueous acetonitrile solution at pH 7.0. Probe 1 showed absorption at 451 nm and a strong fluorescence emission at 537 nm (Φ_F=0.33). The capture of Zn²⁺ by the receptor resulted in the deprotonation of the secondary amine conjugated to 1,8-naphthalimide so that the electron-donating ability of the N atom would be greatly enhanced; thus probe 1 showed a 56 nm red-shift in absorption (507 nm) and fluorescence spectra (593 nm, Φ_F=0.14), respectively, from which one could sense Zn²⁺ ratiometrically and colorimetrically. The deprotonated complex, [(1-H)/Zn]⁺, was calculated at m/z 619.1800 and measured at m/z 618.9890. In contrast to these results, the emission of 1 was thoroughly quenched by Cu²⁺, Co²⁺, and Ni²⁺. The addition of other metal ions such as Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Fe³⁺, Mn²⁺, Al³⁺, Cd²⁺, Hg²⁺, Ag⁺, and Pb²⁺ produced a nominal change in the optical properties of 1 due to their low affinity to probe 1. This means that probe 1 has a very high fluorescent imaging selectivity to Zn²⁺ among metal ions.     

A colorimetric and fluorescent chemosensor for detection of Hg2+ using counterion exchange of cationic polydiacetylene

In this study, a colorimetric and fluorescent chemosensor for mercury ions (Hg²⁺) was developed. Cationic polydiacetylene (PDA) vesicles with a quaternary ammonium cation and iodide as a counterion show a blue-to-red color transition; the color change is accompanied by a fluorescence enhancement in selective response to Hg²⁺ ions because of a perturbation of the ene–yne conjugated backbone induced by counterion exchange. It allows for selective detection of Hg²⁺ with the naked eye and the sensor is used to determine Hg²⁺ concentrations in tap water samples.     

A new fluorescent as well as chromogenic chemosensor for anions based on an anthracene carbamate derivative

A new fluorescent as well as chromogenic anion sensor, 1,8-anthradiol bis(N-phenylcarbamate) 2, was synthesized. It exhibits new selective red-shifted absorption and fluorescence bands with F⁻ and AcO⁻, which could be attributed to the anthracene moiety directly involved in the bonding interaction with the anions.     

Highly Effective Fluorescent Sensor for Hg2+ in Aqueous Solution

A new anthracene fluorophore senses Hg²⁺ selectively in aqueous solution. Among the metal ions examined, fluorescent chemosensor 1 shows selective large CHEQ effects with Hg²⁺ and Ag⁺ at pH 7.     

A novel ratiometric fluorescent Fe sensor based on a phenanthroimidazole chromophore

Phenanthroimidazole derivative 1 has been developed as a rare example of ratiometric fluorescent sensors for Fe³⁺. Interestingly, upon treatment with Fe³⁺, the sensor displayed a ratiometric fluorescent response with an enhancement of the ratios of emission intensities at 440 and 500 nm from 0.36 to 3.24. The detection range of the sensor for Fe³⁺ is in the 1.0 × 10⁻⁵-1.5 × 10⁻⁴ M concentration range and the detection limit is 5.26 × 10⁻⁶ M. In addition, the sensor showed good selectivity to Fe³⁺ with the selectivity coefficients (KFe3+=SFe3+/S₀) of Fe³⁺ over other metal ions tested in the range of 5-68.     

A ratiometric fluorescent chemosensor for Al in aqueous solution based on aggregation-induced emission and its application in live-cell imaging

A ratiometric fluorescent chemosensor 1 was developed for the detection of Al³⁺ in aqueous solution based on aggregation-induced emmision (AIE). The chemosensor showed the fluorescence of its aggregated state and Al³⁺-chelated soluble state in the absence and in the presence of Al³⁺, respectively, and resulted in a fluorescence ratio (I₄₆₁/I₅₃₇) response to Al³⁺ in neutral aqueous solution at a detection limit as low as 0.29 μmol L⁻¹. The method was also highly selective to Al³⁺ over other physiological relevant metal ions investigated in this study. Taking advantage of its AIE characteristics, the chemosensor was successfully applied on test papers for simple and rapid detection of Al³⁺. Moreover, the application of 1 for the imaging of Al³⁺ in living cells by ratiometric fluorescence changes was also achieved.     

A chloroacetate based ratiometric fluorescent probe for cysteine detection in biosystems

The specific detection of cysteine (Cys) over homocysteine (Hcy), glutathione (GSH) and other amino acids is of great significance for studying its biological functions as well as for the diagnosis of related diseases. Chloroacetyl group was often used as a reaction site for cysteine fluorescent probes for its sensitivity and selectivity. However, high background fluorescence and low stability are common problems encountered by such probes. Here, four chloroacetyl group based fluorescent probes (C1, C2, C3, and H4) was synthesized for a comparative study. We found that the inefficient quenching ability of chloroacetyl group turned into an advantage when connected with a ratiometric fluorophore. With the modification of chloroacetyl group, probe H4 displayed excellent ratiometric property and great selectivity for Cys, the stability was also improved. Additionally, the probe was successfully applied for quantitative detection of Cys in fetal bovine serum and real-time imaging in living HeLa cells with low toxicity.     

Colorimetric and ratiometric fluorescent detection of bisulfite by a new HBT-hemicyanine hybrid

A novel HBT-hemicyanine hybrid was prepared. This hybrid not only displays a large red-shifted (Δλ = 125 nm) emission compared to the well known ESIPT dye HBT, but also can be used as a new probe for rapid, colorimetric and ratiometric fluorescent detection of bisulfite with high selectivity and sensitivity in aqueous solution. The detection limit of this probe for HSO₃⁻ was calculated to be about 56 nM with a linear range of 0–25 μM. The potential application of this probe was exampled by detection of bisulfite in real food samples and living cells. Overall, this work not only provided a new ratiometric sensing platform, but also provided a new promising colorimetric and ratiometric fluorescent probe for bisulfite.     

Preparation of graphene quantum dots based core-satellite hybrid spheres and their use as the ratiometric fluorescence probe for visual determination of mercury(II) ions

We herein proposed a simple and effective strategy for preparing graphene quantum dots (GQDs)-based core-satellite hybrid spheres and further explored the feasibility of using such spheres as the ratiometric fluorescence probe for the visual determination of Hg²⁺. The red-emitting CdTe QDs were firstly entrapped in the silica nanosphere to reduce their toxicity and improve their photo and chemical stabilities, thus providing a built-in correction for environmental effects, while the GQDs possessing good biocompatibility and low toxicity were electrostatic self-assembly on the silica surface acting as reaction sites. Upon exposure to the increasing contents of Hg²⁺, the blue fluorescence of GQDs can be gradually quenched presumably due to facilitating nonradiative electron/hole recombination annihilation. With the embedded CdTe QDs as the internal standard, the variations of the tested solution display continuous fluorescence color changes from blue to red, which can be easily observed by the naked eye without any sophisticated instrumentations and specially equipped laboratories. This sensor exhibits high sensitivity and selectivity toward Hg²⁺ in a broad linear range of 10 nM–22 μM with a low detection limit of 3.3 nM (S/N = 3), much lower than the allowable Hg²⁺ contents in drinking water set by U.S. Environmental Protection Agency. This prototype ratiometric probe is of good simplicity, low toxicity, excellent stabilities, and thus potentially attractive for Hg²⁺ quantification related biological systems.     

Novel fluorescent cyanide-selective chemosensor based on a functionalised pillar[5]arene copper(II) complex

As a novel macrocyclic host, pillar[5]arene can selectively recognise guest molecules in organic solvents. In this study, a fluorescent chemosensor composed of a functionalised-pillar[5]arene and Cu²⁺ metal complex (PN–Cu), which shows good selectivity for CN^? anions, has been designed and synthesised. Complexation between PN–Cu and anions has been probed by means of various fluorescence-based methods. PN–Cu, as a turn-on fluorescence chemosensor showed high selectivity towards CN^? ions in comparison to other anions, and its detection limit for CN^? was calculated as 9.03 × 10^?7 M. The PN–Cu sensor can serve as a recyclable component in sensing materials. Moreover, the interaction between the singly functionalised pillar[5]arene and Cu²⁺ has been probed through various tests. Based on the remarkable selectivity of the chemosensor PN–Cu, we propose that it might be used as a potential material for CN^? recognition.     

Ratiometric chemosensor for fluorescent determination of Zn2+ in aqueous ethanol

A new ratiometric and selective fluorescent chemosensor (1) for quantification of zinc ions in aqueous ethanol has been synthesized and investigated in this work. In an environmentally friendly media of 30% (v/v) water/ethanol and 10 mM Tris-HCl neutral buffer (pH 7.03), 1 displayed selective Zn²⁺ ratiometric fluorescence response, with a dynamic working range of 1.0-8.0 μM and a detection limit of 0.5 μM Zn²⁺. The determination of Zn²⁺ in synthesized water sample was also successful.     

A dual-function chemosensor based on coumarin for fluorescent turn-on recognition of Hg2+ and colorimetric detection of Cu2+ in aqueous media

A novel coumarin derivative CTT was synthesized via the condensation of 7-(N,N-diethylamino) coumarin-3-aldehyde with 5-amino-1,3,4-thiadiazole-2-thiol and its structure was characterized using infrared spectroscopy (IR), ¹H NMR, mass spectrometry (MS) techniques, and elemental analysis. The recognition properties of CTT with metal ions were investigated in CH₃CN–H₂O (v/v = 1/1) solution using UV–vis absorption and fluorescence emission spectrum method. The results showed that CTT could monitor Cu²⁺ and Hg²⁺ simultaneously as a dual-function chemosensor in CH₃CN–H₂O (v/v = 1/1). CTT could be used to detect Cu²⁺ colorimetrically; when using CTT, a color change from yellowish-brown to yellowish-green could be readily observed by the naked eye. CTT showed turn-on fluorescent recognition of Hg²⁺, the fluorescence enhancement was attributed to the inhibited C=N isomerization and the obstructed excited state intramolecular proton transfer (ESIPT) of CTT. The recognition mechanism of CTT for Cu²⁺ and Hg²⁺ was studied by experiments and theoretical calculations, respectively. Therefore, CTT has the ability to be a “single chemosensor for dual targets.”     

A multifunctional aggregation-induced emission (AIE)-active fluorescent chemosensor for detection of Zn2+ and Hg2+

An aggregation-induced emission (AIE)-active fluorescent chemosensor based on a tetraphenylethene (TPE) unit has been successfully designed and synthesized. Interestingly, the luminogen could detect Zn²⁺ selectively in a THF solution with the detection limit of 1.24 × 10⁻⁶ mol L⁻¹. Meanwhile, the luminogen could also detect Hg²⁺ selectively in a THF-water mixture with the water content of 90%, and the detection limit was 2.55 × 10⁻⁹ mol L⁻¹. Furthermore, the solid-state mechanochromic fluorescence behavior of the luminogen was investigated systematically. Indeed, the AIE-active luminogen also exhibited reversible mechanofluorochromic phenomenon involving fluorescent color change from blue to green, and powder X-ray diffraction results indicated that the switchable morphology conversion between crystalline and amorphous states was responsible for this mechanochromism phenomenon.     

A fluorescent chemical sensor for Hg(II) based on a corrole derivative in a PVC matrix

A fluorescent chemical sensor for Hg(II) using 5,10,15-tris(pentafluorophenyl)corrole (H₃(tpfc)) as fluorophore is described in this paper. The response of the sensor is based on the fluorescence quenching of H₃(tpfc) by coordination with Hg(II). H₃(tpfc) based sensor shows a linear response towards Hg(II) in the concentration range from 1.2 × 10⁻⁷ to 1.0 × 10⁻⁴ M, with a working pH range from 5.0 to 8.0. The response time for Hg(II) concentration ≤1.0 × 10⁻⁵ M is less than 5 min. The sensor shows good selectivity for Hg(II) over alkali, and alkaline earth, and most of transition metal cations. The effect of the composition of the sensor membrane has been studied and the experimental conditions optimized. The corrole based sensor membrane can be easily regenerated just by washing with blank buffer solution after each measurement. The sensor has been used for determination of Hg(II) in water samples with satisfactory results.