New fluorescent chemosensors for metal ions in solution

After a brief introduction on the main transduction mechanisms for metal ion detection by fluorescence, this paper reviews ligand molecules containing fluorophores synthesized and employed in metal ions sensing in solution in the last few years. With the aim of making more readable the paper we have organized it by dividing the subject first for type of fluorophore, then type of metal ion. Because of many acronyms a glossary has been inserted.     

Development of nanomaterial chemosensors for toxic metal ions sensing

Heavy metal ions are harmful to aquatic life and humans owing to their high toxicity and non‐biodegradability, so their removal from wastewater is an important task. Therefore, this work focuses on designing suitable, simple and economical nanosensors to detect and remove these metal ions with high selectivity and sensitivity. Based on this idea, different types of mesoporous materials such as hexagonal SBA‐15, cubic SBA‐16 and spherical MCM‐41, their chloro‐functionalized derivatives, as well as 4‐(4‐nitro‐phenylazo)‐naphthalen‐1‐ol (NPAN) azo dye have been synthesized, with the aim of designing some optical nanosensors for metal ions sensing applications. The mentioned azo dye has been anchored into the chloro‐functionalized mesoporous materials. The designed nanosensors were characterized using scanning and transmission electron microscopy as well as Fourier transform infrared and UV–visible spectral analysis, nitrogen adsorption–desorption isotherms, low‐angle X‐ray diffraction and thermogravimetric analyses. Their optical sensing to various toxic metal ions such as Cd (II), Hg (II), Mn (II), Fe (II), Zn (II) and Pb (II) at different values of pH (1.1, 4.9, 7 and 12) was investigated. The optimization of experimental conditions, including the effect of pH and metal ion concentration, was examined. The experimental results showed that the solution pH had a major impact on metal ion detection. The optical nanosensors respond well to the tested metal ions, as reflected by the enhancement in both absorption and emission spectra upon adding different concentrations of the metal salts and were fully reversible on adding ethylene diamine tetra acetic acid or citric acid to the formed complexes. High values of the binding constants for the designed nanosensors were observed at pHs 7 and 12, confirming the strong chelation of different metals to the nanosensor at these pHs. Also, high binding constants and sensitivity were observed for NPAN‐MCM‐41 as a nanosensor to detect the different metal ions. From the obtained results, we succeeded in transforming the harmful azo dye into an environmentally friendly form via designing of the optical nanosensors used to detect toxic metal ions in wastewater with high sensitivity.     

Recent progress in fluorescent and colorimetric chemosensors for detection of precious metal ions (silver, gold and platinum ions)

Due to the wide range of applications and biological significance, the development of optical probes for silver, gold and platinum ions has been an active research area in the past few years. This tutorial review focuses on the recent contributions concerning the fluorescent or colorimetric sensors for these metal ions, and is organized according to their structural classifications (for Ag(+) detection) and unique mechanisms between the sensors and metal ions (for Au(3+) and Pt(2+) detection).     

8-Hydroxyquinoline benzoates as highly sensitive fluorescent chemosensors for transition metal ions

[graph: see text] 8-Hydroxyquinoline benzoates were developed as a new set of 8-HQ derivatives for highly sensitive fluorescent chemosensors for transition metal ions. A prominent fluorescence enhancement was found in the presence of transition metal ions such as Hg2+ and Cu2+, and this was suggested to result from the suppression of radiationless transitions from the npi state in the chemosensors.     

石墨烯基复合材料去除和检测重金属离子的研究进展

石墨烯具有超大的比表面积、较快的载流子迁移速率和优异的电催化活性,广泛用于环境保护与检测领域。过去几年,基于石墨烯的大批高效吸附剂和传感器均被开发并应用于重金属离子的污染治理。本文详细阐述了石墨烯基复合材料在重金属离子去除和检测方面的研究进展,同时比较了不同方法的优缺点,最后对后续研究方向进行了展望。     

Probing biologically and environmentally important metal ions with fluorescent chemosensors: Thermodynamic versus optical response selectivity in some study cases

The reciprocal influence of the thermodynamic (binding) selectivity and the sensing (optical response) selectivity of fluorescent chemosensors in determining their efficiency in probing biologically and environmentally important metal ions in real matrices will be discussed on the basis of some study cases from the work of the authors.     

Supramolecular optical chemosensors for organic analytes

Supramolecular optical chemosensors are abiotic molecular devices that bind analytes by noncovalent interactions, producing a change in light absorption or fluorescence. This review summarizes recent progress in the development of such chemosensors for organic analytes based on artificial receptors. Important design considerations, such as analyte affinity, choice of chromophore or fluorophore, binding selectivity, and optical signaling mechanism are briefly discussed. Chemists have fashioned chemosensors from a wide range of molecular structures, including polyalcohols, crown ethers, calixarenes, helicenes, sterically geared tripods, metal complexes, pinwheels, porphyrins, and fused-ring heterocycles. Analytes of interest include amines, carboxylic acids, amino acids, hydroquinones, alkaloids, carbohydrates, peptides, urea and creatinine.     

Thiazole-tethered biaryls as fluorescent chemosensors for the selective detection of Fe3+ ions

3-Amino-5-(thiazol-2-yl)-[1,1′-biaryl]-2,4-dicarbonitriles have been synthesized employing a facile one-pot pseudo four-component domino strategy. All these thiazole-tethered biaryls exhibited blue fluorescence under UV lamp. Based on the high relative quantum yield, three compounds namely, 4a , 4d , and 4i , were chosen to explore the metal interference studies. Against several metal ions, these three thiazole-tethered biphenyl probes were found to be effective fluorescent chemosensors for the selective and sensitive detection of Fe³⁺ ions with a lower detection limit of 0.18, 0.12, and 0.16 μM, respectively.     

Functionalized magnetic nanoparticles as chemosensors and adsorbents for toxic metal ions in environmental and biological fields

Functionalized magnetic nanoparticles, composed of both inorganic and organic components, have recently been examined as promising platforms for detection and separation applications. This unique class of nanomaterials can retain not only beneficial features of both the inorganic and organic components, but can also provide the ability to systematically tune the properties of the hybrid materials through the combination of appropriate functional components. This tutorial review focuses on the recent development of functionalized magnetic nanoparticles for use in biological and environmental applications, in which these chromogenic and fluorogenic chemosensors can selectively detect and separate specific toxic metal ions.     

Novel azo-dye quinazolinones as colorimetric chemosensors for detection of cobalt and ferrous ions in aqueous medium

Highly efficient azo-day quinazolinone derivatives carrying a π bond and OH electron donor groups have been designed, synthesized, and evaluated as colorimetric chemosensors for detecting metal ions in biological and environmental samples, which was further supported by the DFT studies and UV–vis titration experiment. The 3-amino-2-styrylquinazolin-4(3H)-one (1) was directed to react with phenols during a diazotization type reaction to form a series of azo-day 3-(diazenyl)-2-(styryl)quinazolin-4(3H)-one (4a-e), which could not only have been confirmed by FTIR, H¹NMR, C¹³NMR, Ms and elemental analysis but could also be easily used for the detection of metal ions. Compound 4c exhibited a rapid qualitative and quantitative method for the detection of Co^II at λ max (582 nm) and Fe^II at λ max (566 nm) in an aqueous solution. The current study introduces a facile, low cost, more specific and selective chemosensor for detecting trace amounts of cobalt and ferrous ions.     

Dye-ligand immobilized IPNs membrane for removal heavy metal ions

We have developed a novel approach to obtain high metal sorption capacity utilizing a membrane containing chitosan and an immobilized reactive dye (i.e. Reactive Yellow-2). The composite membrane was characterized by SEM, FT-IR, swelling test, and elemental analysis. The membrane has uniform small pores distribution and the pore dimensions are between 5 and 10 μm, and the HEMA:chitosan ratio was 50:1. The reactive dye immobilized composite membrane was used in the removal of heavy metal ions [i.e., Pb(II), Hg(II) and Cd(II)] from aqueous medium containing different amounts of these ions (5-600 mg l⁻¹) and at different pH values (2.0-7.0). The maximum adsorption capacities of heavy metal ions onto the composite membrane under non-competitive conditions were 64.3 mmol m⁻² for Pb(II), 52.7 mmol m⁻² for Hg(II), 39.6 mmol m⁻² for Cd(II) and the affinity order was Pb(II) > Hg(II)>Cd(II).     

Tautomeric crown-containing chemosensors for alkali-earth metal cations

Crown-containing arylimines of 5-hydroxy- and 5-hydroxy-6-nitro-2,3-diphenylbenzo[b]furan-4-carbaldehydes were synthesized and their structure, spectral, luminescent, and complexing properties were studied by means of ¹H and ¹³C NMR, IR, UV, and mass-spectrometry. In solution, these compounds exist as equilibrium mixtures of benzenoid and quinoid tautomers. The relative concentration of the quinoid form increases in the order of solvents: toluene, acetonitrile, 2-propanol, chloroform. The presence in the benzo[b]furan moiety of a strong withdrawing 6-NO₂ group favors stabilization of the quinoid tautomer. This finding is in accord with the results of the DFT B3LYP/6-311++g(d,p) calculations. Complexation of 5-hydroxy-6-nitro-2,3-diphenyl-1-benzofuran-4-carbaldehyde crown-containing imines with alkali and alkali-earth metal ions shifts the tautomeric equilibrium to the quinoid forms and is accompanied by blue shifts of the emission spectra. The Schiff bases obtained represent a new type of fluorescent tautomeric chemosensor for Mg²⁺, Ca²⁺ (benzo-15-crown-5 derivative), and Ba²⁺ (benzo-18-crown-6 derivative) displaying diagnostic changes in both absorption and emission spectra.     

Triphenylamine‐based fluorescent conjugated copolymers with pendant terpyridyl ligands as chemosensors for metal ions

Two well‐defined triphenylamine‐based fluorescent conjugated copolymers with pendant terpyridyl ligands were synthesized through Suzuki coupling polymerization and were further characterized by ¹H‐NMR, ¹³C‐NMR, gel permeation chromatography, Infrared, and UV‐vis spectra. Polymer P‐1 , terpyridine‐bearing poly(triphenylamine‐alt‐fluorene) with a high fluorescence quantum yield (62%) shows much higher sensitivities toward Fe³⁺, Ni²⁺, and Cu²⁺ as compared with the other metal ions investigated. Especially, Fe³⁺ can lead to an almost complete fluorescence quenching of polymer P‐1 . Whereas, the analogous polymer P‐2 , in which N‐ethylcarbazole repeat units replace the fluorene units in P‐1 , shows a very poor selectivity. It demonstrates that polymers with a same receptor may show different sensitivity to analytes owing to their different type of backbones. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1310–1316, 2010     

基于咔唑衍生物的荧光化学传感器的合成及其对金属离子的选择性识别性能

以咔唑为原料合成了2个荧光化学传感器,所得化合物的组成和结构经元素分析以及质谱、红外光谱、核磁共振氢谱验证.通过在25℃下进行荧光光谱滴定,研究了传感器在体积比为1∶1的二甲基亚砜/水缓冲溶液[三羟甲基氨基甲烷盐酸盐(Tris-HCl),pH=7.4]中对Cu2+和Fe3+的选择性识别作用.结果表明,所合成的传感器与Cu2+和Fe3+形成1∶1的配合物并导致荧光猝灭,并对Cu2+离子和Fe3+离子具有较高的选择性识别和荧光传感性能.     

The synthesis of luminescent lanthanide-based chemosensors for the detection of zinc ions

Herein, we report the synthesis of two lanthanide-based chemosensors, Tb-5 and Eu-6, designed to sense free zinc ions (Zn²⁺) in aqueous solutions. The Tb-5 complex features a bis(2-pyridinylmethyl)amine moiety as a zinc(II)-responsive lanthanide-sensitising ‘antenna’, while Eu-6 incorporates a quinoline-based moiety for this purpose. Luminescence enhancements of 210% and 340% are observed upon addition of Zn²⁺ ions to Tb-5 and Eu-6, respectively. Both sensors are selective for Zn²⁺ ions over several other cations of environmental significance.     

New synthesized ligands for detection of heavy metal ions

Some new chemo-sensors (4,4'-((1E,1′E)-(2,2′-dichloro-[1,1′-biphenyl]-4,4′-diyl)bis(diazene-2,1-diyl))bis(3,5-dihydroxybenzoic acid), 4-((E)-(4-(N-(4-((E)-(4-carboxy-2,6-dihydroxyphenyl)diazenyl)phenyl)sulfamoyl)phenyl)diazenyl)-3,5-dihydroxybenzoic acid, 4-((E)-(4-((4-((E)-(4-carboxy-2,6-dihydroxyphenyl)diazenyl)-2-sulfophenyl)amino)phenyl)diazenyl)-3,5-dihydroxybenzoic acid) were synthesized. These synthesized sensors were then characterized by FTIR, TLC, UV–Visible spectrophotometry, and NMR techniques. The sensors showed the best results for detection of all type of heavy metal ions simply by changing the colour of metal ion solution and by shifting in the λ_max values of sensors due to interactions.     

Quaternary ammonium salt-based chromogenic and fluorescent chemosensors for fluoride ions

Chemosensors 5-7 possessing a quaternary ammonium cation (for electrostatic interactions) and an N-H group(s) (for H-bonding) as recognition sites and an anthracene-9,10-dione as both a chromogenic and fluorescent moiety exhibit absorption and emission changes with fluoride ions only. No significant response to other anions such as Cl⁻, Br⁻, I⁻, , CH₃COO⁻, , and is observed. The dual emission at λ_max 580 nm (free 5/6) and λ_max 510 and 540 nm (5/6 + F⁻) in chemosensors 5 and 6 enables ratiometric analysis of fluoride ions.     

Fluorescent chemosensors for metal ions based on 3-(2-benzoxazol-5-yl)alanine skeleton

The ability of new chelate ligands, benzoxazol-5-yl-alanine derivatives substituted in position 2 by heteroaromatic substituent, to form complexes with selected metal ions in acetonitrile are studied by means of absorption and steady-state and time-resolved fluorescence spectroscopy. Among the ligands studied, only azaaromatic derivatives form stable complexes with transition metal ions in the ground state. Their absorption bands are bathochromically shifted enabling to use those ligands as ratiometric sensors. The fluorescence of each ligand is quenched by metal ions, however, in the presence of Cd(II) and Zn(II) ions a new red shifted emission band is observed.      

A versatile amphiprotic cotton fiber for the removal of dyes and metal ions

Adsorption is an efficient method to combat the important issues of water pollution caused by dyes and metal ions. However, due to the surface charge diversity of pollutants, there is a pressing need to develop an all-round, efficient, cheap and environmentally friendly adsorbent. To this end, this work synthesized an amphiprotic adsorbent based on cotton fibers, which were chemically modified with a cationic monomer (3-chloro-2-hydroxypropyl trimethyl ammonium chloride) and anionic monomer (2-acrylamide-2-methyl propane sulfonic acid) respectively. The resultant amphiprotic cotton (AP-cotton) can cope with both of anionic and cationic pollutants. Its adsorption behavior as influenced by the pH value, adsorption time and initial concentration of various adsorbates was investigated. The results demonstrate that the adsorption equilibrium was reached within 4 h for Congo red (CR) and methylene blue (MB), 2 h for Cu²⁺ and 3 h for Pb²⁺, respectively. Adsorption kinetics showed that the adsorption rate was well fitted with the pseudo-second-order rate model, and the best adsorption isotherms fitted the Langmuir model. The Langmuir maximum adsorption capacities were 175.1 mg/g for CR, 113.1 mg/g for MB, 88.9 mg/g for Cu²⁺ and 70.6 mg/g for Pb²⁺, respectively, and the adsorption capacities could be maintained above 90 % after six regenerations. The all-round adsorption capacity and good regeneration performance of AP-cotton benefited from its hollow, flat-banded structure and amphiprotic characteristic. Therefore, AP-cotton exhibited a much better application potential compared with many other reported adsorbents based on natural materials.     

Inorganic particulates in removal of toxic heavy metal ions

The removal behavior of amorphous aluminum hydroxide for Hg(II) ions from aqueous solutions was investigated by employing a radiotracer technique at micro down to trace level concentrations. The batch type experiments were performed to obtain various physico-chemical parameters, viz., effect of sorptive concentration, temperature and pH. It was observed that the increase in sorptive concentration (from 1·10⁻⁸ to 1·10⁻² mol·dm⁻³), temperature (from 303 to 333K) and pH (from 3.4 to 10.3) apparently favored the uptake of Hg(II) by this solid. Similarly, the presence of anions (six fold) viz., oxalate, phosphate, glycine and EDTA also enhanced the uptake behavior of aluminum hydroxide for Hg(II). Whereas, the added cations viz., Na⁺, K⁺, Ba²⁺, Sr²⁺, Mg²⁺, Cd²⁺ and Fe³⁺ more or less suppressed the removal behavior of the adsorbent. Further, the adsorption process followed the classical Freundlich adsorption isotherm and deductions of various thermodynamic data revealed that the uptake of Hg(II) on aluminum hydroxide followed the ion-exchange type mechanism and thermodynamically it was found to be endothermic in nature. Part IX: Rapid and efficient removal of Hg(II) by hydrous manganese and tin oxides, J. Coll. Interf. Sci., 279 (2004) 61.