Ratiometric and selective fluorescent sensor for CuII based on internal charge transfer (ICT)

A Cu(II)-sensing, ratiometric, and selective fluorescent sensor 1, N-butyl-4,5-di[(pyridin-2-ylmethyl)amino]-1,8-naphthalimide, was designed and synthesized on the basis of the mechanism of internal charge transfer (ICT). In aqueous ethanol solutions of 1, the presence of Cu(II) induces the formation of a 1:1 metal-ligand complex, which exhibits a strong, increasing fluorescent emission centered at 475 nm at the expense of the fluorescent emission of 1 centered at 525 nm. [structure: see text]     

Ratiometric fluorescence chemosensors for copper(II) and mercury(II) based on FRET systems

A system based on FRET mechanism, comprising a coumarin donor and a rhodamine acceptor, was developed for the selective and quantitative detection of metal ions. Fluorescent chemosensors RCs, linked by 1,2-diethylamine, exhibit significant fluorescence enhancement and excellent selectivity toward Cu²⁺. Fluorescent probes CRB and CR6G, linked by hydrazide, function as ratiometric receptors for Cu²⁺ chromogentically and fluorogentically in organic-aqueous media. Furthermore, the characteristic rhodamine-based fluorescence response of CRB (excitation at 550 nm) exhibits high selectivity for Hg(II). The construction of this kind of universal FRET system opens a broader prospect for future design of ratiometric fluorescent probes.     

Selective dendritic fluorescent sensors for Zn(II)

A series of dendritic 8-hydroxyquinoline (8-HQ) and 5-dialkyl(aryl)aminomethyl-8-HQ derivatives were synthesized and their fluoroionophoric properties toward representative alkali, alkaline earth, group IIIA and transition metal ions were investigated. Among the selected ions, Zn(II) enhanced the fluorescence of N-di-(methoxycarbonylethyl)aminoethyl-3-[4-(8-hydroxyquinolin-5-ylmethyl)piperazin-1-yl]-propanoic amide] (7) by 31-fold, while Al(III) caused enhancement to some extent. The absence of any significant fluorescence enhancement by the other ions examined renders 7a highly useful Zn(II)-selective fluorescent sensor.     

Highly sensitive fluorescent sensor for copper (II) based on amplified fluorescence quenching of a water-soluble NIR emitting conjugated polymer

We have synthesized the near-infrared water-soluble conjugated polymer poly[2,5-di(propyloxysulfonate)-1,4-phenylene-ethynylene-9,10-anthrylene (referred to as PPEASO3). Its fluorescence (at wavelengths between 650 and 800?nm following photoexcitation at 550?nm) is efficiently quenched by Cu(II) ions, while other physiologically relevant metal ions do not cause significant quenching at the same concentrations. Under optimum conditions, fluorescence intensity is inversely proportional to the concentration of Cu (II). The calibration curve displays two linear regions over the range of 0–3.2?×?10^?7 mol L^?1 and 3.2?×?10^?7 mol L^?1 to 1.0?×?10^?4 mol L^?1 of Cu(II), respectively. The long-wavelength excitation and emission can substantially reduce interferences by the autofluorescence and light scattering of biological matter under UV excitation. The method was successfully applied to the determination of Cu(II) in synthetic and tea samples.

Novel highly selective fluorescent chemosensors for Zn(II)

Two novel fluorescent Zn²⁺ chemosensors were synthesized in four steps from inexpensive starting materials. They exhibited very strong fluorescence responses to Zn²⁺ and had remarkably high selectivity to Zn²⁺ than other metal ions including Mg²⁺, Ca²⁺, Ni²⁺, Cu²⁺, and Cd²⁺. These two new molecules could be used as low-priced yet high-quality Zn²⁺ chemosensors.     

Spacer layer screening effect: a novel fluorescent film sensor for organic copper(II) salts

A fluorescent film sensor was prepared by chemical assembly of pyrene on a glass plate surface via a long flexible spacer. It was found that the film is highly selective for some organic Cu2+ salts, such as copper acetate and copper propionate. The presence of inorganic Cu2+ salts and other metal(II) acetates, including Ni2+, Co2+, Pb2+, Cd2+, Zn2+, etc., had little effect upon the sensing behavior of the film for copper acetate or copper propionate. The observation was explained by employing a proposed "two-dimensional solution" model. The quenching by copper acetate of the emission of the film is static in nature due to complexation of the spacers to the metal ions. Furthermore, the response of the film sensor to copper acetate is fully reversible. To the best of our knowledge, this film sensor may be the first one that can differentiate greasy copper salts from inorganic copper salts.     

A fluorescent ammonia sensor based on a porphyrin cobalt(II)-dansyl complex

Detecting and measuring the concentration of ammonia is of interest in many scientific and technological areas. A porphyrin based cobalt(II) complex with a dansyl fluorophore has been synthesized and investigated as a ‘turn-on’ fluorescent ammonia sensor. Over sixfold increase in fluorescence emission occurs upon the treatment of NH₃ to [Co(TPP)(Ds-pip)] sensor solution, resulting from NH₃-induced displacement of the axially coordinated fluorophore.     

A fluorescent chemosensor for copper(II) based on a carboxylic acid-functionalized tris(2,2'-bipyridine)-ruthenium(II) complex.

In this research, bis(2,2'-bipyridine)(4-methyl-2,2'-bipyridine-4'-carboxylic acid)ruthenium(II).2PF(6)- complex (1), was first used as a fluorescent chemosensor to recognize Cu(II) in EtOH/H(2)O (1:1, v/v) solution. The response of the sensor is based on the fluorescence quenching of complex 1 by binding with Cu(II). The analytical performance characteristics of the proposed Cu(II)-sensitive chemosensor were investigated. The sensor can be applied to the quantification of Cu(II) with a linear range covering from 5.0 x 10(-8) to 1.0 x 10(-4) M and a detection limit of 4.2 x 10(-8) M. The experiment results show that the response behavior of 1 to Cu(II) is pH independent in medium condition (pH 4.0 - 8.0), and show excellent selectivity for Cu(II) over other transition metal cations.     

Ratiometric fluorescent determination of Zn(II): a new class of tripodal receptor using mixed imine and amide linkages

We synthesized a novel receptor with a unique combination of sp² nitrogen (-CHN-) and carbonyl groups from amide linkages. These two moieties are judiciously incorporated into the receptor design such that these sites simultaneous binding a metal ion may generate a stable five-member ring. The receptor has been used to selectively detect Zn²⁺ through changes in the fluorescence spectra. Upon Zn²⁺ binding with the receptor, the fluorescence band shifted to enhance fluorescence intensity, allowing ratiometric determination of Zn²⁺ concentration.     

A selective fluorescent sensor for Pb(II) in water

A new fluorescent sensor (1) containing bis(2-pyridylmethyl)amine group as a binding moiety for Pb²⁺ was developed. Compound 1 shows selective response to Pb²⁺ over other metal ions in pH 7.0 HEPES buffer solution. The fluorescence intensity enhancement was ascribed to the complex formation between Pb²⁺ and 1 which blocked the photo-induced electron transfer process.     

A photoswitchable Zn (II) selective spiropyran-based sensor

A spiropyran-based fluorescent and photoregenerable receptor, that is, selective towards zinc(II) ions over a series of biologically and environmentally relevant cations has been designed and synthesized. The complex formation gives rise to colour changes that are visible to the naked eye and reversible upon visible light irradiation. ¹H NMR studies confirm that the closed form is converted to the open trans-merocyanine complex upon addition of zinc ions.     

Proton-controllable fluorescent switch based on interconversion of polynuclear and dinuclear copper(II) complexes

The first reversible interconversion process between a one-strand polymeric copper(II) complex {[Cu2(L1)2(ClO4)2](ClO4)2}n (1) and a dicopper(II) helicate [Cu2(L1-2H)2] (2), proceeding via a deprotonation-protonation process, can transduce fluorescence and function as a fluorescent switch simply by introducing a one fiftieth equivalent of coumarine 343 anion, a fluorophore.     

Highly selective ratiometric fluorescent sensor for Cu(II) with two urea groups

A new Naphthalene derivative with two urea groups, 1,8-bis[N-(o-methoxyphenyl)ureido]naphthalene (BMPUN), was synthesized for detecting Cu(II) ratiometrically. Complexation between urea groups of BMPUN and Cu(II) with high selectivity gives rise to a great red-shift from 380 to 440 nm in the emission spectra. The introduction of electron donating groups is helpful to increase the electron density of the nitrogen atom of urea groups and then enhance the ability of complexation for Cu(II).     

Ratiometric fluorescent sensor based on inhibition of resonance for detection of cadmium in aqueous solution and living cells

Although cadmium has been recognized as a highly toxic heavy metal and poses many detrimental effects on human health, the Cd(2+)-uptake and nosogenesis mechanisms are still insufficiently understood, mainly because of the lack of facile analytical methods for monitoring changes in the environmental and intracellular Cd(2+) concentrations with high spatial and temporal reliability. To this end, we present the design, synthesis, and photophysical properties of a cadmium sensor, DQCd1 based on the fluorophore 4-isobutoxy-6-(dimethylamino)-8-methoxyquinaldine (model compound 1). Preliminary investigations indicate that 1 could be protonated under neutral media and yield a resonance process over the quinoline fluorophore. Upon excitation at 405 nm, 1 shows a strong fluorescence emission at 554 nm with a quantum yield of 0.17. Similarly, DQCd1 bears properties comparable to its precursor. It exhibits fluorescence emission at 558 nm (Φ(f) = 0.15) originating from the monocationic species under physiological conditions. Coordination with Cd(2+) causes quenching of the emission at 558 nm and simultaneously yields a significant hypsochromic shift of the emission maximum to 495 nm (Φ(f) = 0.11) due to inhibition of the resonance process. Thus, a single-excitation, dual-emission ratiometric measurement with a large blue shift in emission (Δλ = 63 nm) and remarkable changes in the ratio (F(495 nm)/F(558 nm)) of the emission intensity (R/R(0) up to 15-fold) is established. Moreover, the sensor DQCd1 exhibits very high sensitivity for Cd(2+) (K(d) = 41 pM) and excellent selectivity response for Cd(2+) over other heavy- and transition-metal ions and Na(+), K(+), Mg(2+), and Ca(2+) at the millimolar level. Therefore, DQCd1 can act as a ratiometric fluorescent sensor for Cd(2+) through inhibition of the resonance process. Confocal microscopy and cytotoxicity experiments indicate that DQCd1 is cell-permeable and noncytotoxic under our experimental conditions. It can indeed visualize the changes of intracellular Cd(2+) in living cells using dual-emission ratiometry.     

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.     

Fluorescence resonance energy transfer disposable sensor for copper(II)

A disposable sensor has been developed for the measurement of copper(II) concentration in aqueous solution based on a change in the fluorescence of porphyrazine 2,7,12,17-tetra-tert-butyl-5,10,15,20-tetraaza-21H,23H-porphine (TP). The sensor was constructed by spin-coating a polyester support with a PVC solution containing TP, a plasticizer, the chelating agent Zincon and the ion-pairing benzetonium chloride. The measurement principle is based on the radiationless resonance energy transfer (RET) from TP immobilized in membrane, and acting as fluorescence donor, to Zincon acting as an acceptor induced by copper(II). The absorption spectrum of the Zincon-Cu(II) complex presents adequate overlapping with the emission spectrum of TP, producing a useful analytical signal by the RET process.The disposable sensor responds to copper(II) irreversibly over a dynamic range from 0.039 to 14 μmol L⁻¹ (2.5-890 μg L⁻¹) with a sensor-to-sensor reproducibility (relative standard deviation RSD) of 1.9%, as log aCu2+, at the medium level of the range and a response time of 10 min. The performance of the optical disposable sensor was tested for the analysis of copper in different types of natural waters (river, well, spring and swimming pool), validating results against a reference procedure.     

Both visual and ratiometric fluorescent sensor for Zn2+ based on spirobenzopyran platform

A ratiometric fluorescent Zn²⁺ chemosensor, SPQH, based on spirobenzopyran platform, was synthesized. In aqueous HEPES 7.4 buffer solution, upon chelation with Zn(II), SPQH demonstrates high selectivity and subnanomolar sensitivity for zinc ion with 36-fold enhancement in the NIR fluorescence output.     

A novel small molecule fluorescent sensor for Zn2+ based on pyridine-pyridone scaffold

The development of a water-soluble and small molecular weight fluorescent probe, 3-(4-methoxyphenyl)-4-(methylsulfanyl)-6-(pyridin-2-yl)pyridin-2(1H)-one (3), for detecting Zn²⁺ based on pyridine-pyridone skeleton is reported. We observed a clear chelation enhanced fluorescence effect of 3 in the presence of Zn²⁺. Other fluorescent properties of 3 are discussed.     

Phosphorescent sensor for robust quantification of copper(II) ion

A phosphorescent sensor based on a multichromophoric iridium(III) complex was synthesized and characterized. The construct exhibits concomitant changes in its phosphorescence intensity ratio and phosphorescence lifetime in response to copper(II) ion. The sensor, which is reversible and selective, is able to quantify copper(II) ions in aqueous media, and it detects intracellular copper ratiometrically.