A highly selective and sensitive fluorescent turn-on chemosensor for Al3+ based on a chromone Schiff base

A Schiff-base fluorescent sensor, 7-methoxychromone-3-carbaldehyde-(3′,4′-dimethyl)pyrrole hydrazone (MCPH), was synthesized. The new sensor showed high selectivity for Al³⁺ over other metal ions examined in acetonitrile. Upon binding Al³⁺, a significant fluorescence enhancement with a turn-on ratio over 101-fold was triggered. The detection limit of MCPH for Al³⁺ was 2.5?×?10^?7?mol?L^?1.     

Carbazole-based Schiff base: A sensitive fluorescent ‘turn-on’ chemosensor for recognition of Al(III) ions in aqueous-alcohol media

Carbazole-based Schiff base chemosensor was synthesized in one-pot synthesis using 2-hydroxy-1-naphtaldehyde for fluorescent sensing of Al³⁺ ions. Characterization of the ligand (L) was revealed through spectroscopic and physicochemical techniques. The fluorescence emission responses of L to various metal ions and anions were investigated. The chelation was studied by UV–vis, ¹H NMR, LC-MS/MS, fluorescence titration and Job’s plot analysis. Bathochromic shift resulted from charge transfer from L to electrophilic Al³⁺ ion was observed in the chelation of L with Al³⁺. The potentiality of L to be a distinguished probe to detect Al³⁺ ions was due to a chelation enhanced fluorescence (CHEF) effect, concomitant with noticeable fluorescent enhancement. A significant fluorescence enhancement at 533 nm was observed in ethanol–water (1:1, v/v) solution upon addition of Al³⁺ along with a distinct color change from yellow to white. Non-fluorescent ligand exposed highly sensitive turn-on fluorescent sensor behavior for selectively sensing Al³⁺ ions via 1:1 (ligand:metal) stoichiometry. The ligand’s specificity in the existence of other tested metal ions and anions indicated no observation in color change. The ligand-Al³⁺ complex formation was reversible upon addition of chelating agent EDTA. The ligand interacted with Al³⁺ ions with an association constant of K_a = 5 × 10⁴ M^?1. The limit of detection (LOD) was found to be 2.59 × 10^-7 M. The synthesized Schiff base could efficiently detect Al³⁺ ions as a fluorescent sensor.     

Fluorescent chemosensor based-on naphthol-quinoline for selective detection of aluminum ions

In this study, an assay to quantify the presence of aluminum ions with a receptor containing naphthol and quinoline moieties was developed using a turn-on fluorescence enhancement approach. Upon treatment with aluminum ions, the fluorescence of the receptor was enhanced at 510 nm due to the formation of a complex between the ligand and aluminum ions at room temperature. As the concentration of Al³⁺ was increased, the fluorescence gradually increased. Other metal ions, such as K⁺, Ag⁺, Ca²⁺, Mg²⁺, Zn²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺, Cr³⁺, Fe³⁺, In³⁺, had no significant effect on the fluorescence.     

Thiophene and diethylaminophenol-based “turn-on” fluorescence chemosensor for detection of Al3+ and F− in a near-perfect aqueous solution

A new fluorescent sensor 1, based on thiophene and diethylaminophenol moieties, has been synthesized and its binding capabilities for metal-ion and anion recognition were investigated. The sensor 1 showed ‘turn-on’ fluorescence in the presence of Al³⁺ and F^?. The sensing behaviors of 1 with Al³⁺ and F^? were studied by using photophysical experiments, ¹H NMR titration, and ESI-mass spectrometry analysis. The detection limits for the analysis of Al³⁺ and F^? were found to be 0.41 μM and 14.36 μM, respectively, which are below the WHO guidelines for drinking water (7.41 μM for Al³⁺ and 79 μM for F^?). Moreover, turn-on fluorescence of 1 toward Al³⁺ and F^? caused by intramolecular charge transfer (ICT) was well explained by density functional theory (DFT) calculations. Importantly, 1 could be used to detect Al³⁺ in the living cells.     

A biacylhydrazone-based chemosensor for fluorescence ‘turn-on’ detection of Al3+ with high selectivity and sensitivity

A simple Al³⁺ fluorescent chemosensor (1) based on diacylhydrazone has been designed and synthesized by the condensation reaction of 2-hydroxy naphthaldehyde and metaphthalic hydrazide. The chemosensor 1 displays a specific and sensitive response to Al³⁺ over other cations in DMSO solution. Upon the addition of DMSO solution of Al³⁺, the sensor 1 shows an immediate fluorescence ‘turn-on’ response and emitting strong blue emission with visible color change from colorless to green. The fluorescence quantum yield enhanced from 7.24% to 48.68%. Meanwhile, the fluorescence and UV absorption spectra detection limits of the chemosensor 1 for Al³⁺ were 2.0 × 10^?7 M and 5.6 × 10^?7 M respectively, indicating the high sensitivity of 1 to Al³⁺. Furthermore, test strips based on 1 were fabricated, which could be used as a convenient test kit for the detection of Al³⁺ and an efficient Al³⁺ controlled fluorescent security display materials.     

Interaction of a Schiff-base fluorescent sensor with Al3+: experimental and computational studies

A fluorescent Al³⁺ chemo-sensor, 1-phenyl-3-methyl-5-hydroxypyrazole-4-acetone-(3′,4′-dimethylpyrrole-2′-formyl) hydrazone (L), has been synthesized and characterized. L can detect Al³⁺ in ethanol solution with a significant fluorescence enhancement of a turn-on ratio over 155-fold due to the formation of a 1?:?1 complex which is based on the molar ratio between L and Al³⁺ ions, and the 1?:?1 stoichiometric complexation can be obtained from density functional theory calculations. No significant interference of other metal ions such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe³⁺, Cr³⁺, Pb²⁺, and Ag⁺ was found. The detection limit for Al³⁺ was 5?×?10^?9?M in ethanol.     

A near-infrared emissive Al sensing platform for specific detection in solution,cells and probing DNase activity

A new tricarbocyanine-based chemosensor exhibited a dramatic Al³⁺-specific fluorescence turn-on response in the near-infrared (NIR) region. The receptor was found to be highly selective towards Al³⁺ over other metal ions in physiological condition. The sensor was non-toxic and could thus be employed as an imaging probe for detecting intracellular Al³⁺ in live cells. Interestingly, upon interaction with DNA in solution, the L–Al³⁺ ensemble rendered tracking of DNase activity in solution through a systematic reduction in the fluorescence emission intensity.     

A fluorescent sensor for Al3+ based on a photochromic diarylethene with a hydrazinobenzothiazole Schiff base unit

A new fluorescent turn-on chemosensor for Al³⁺ based on a diarylethene unit was designed and synthesized. Photochromism, fluorescence switch, and metal ion recognition behaviors of this diarylethene derivative were investigated by absorption and fluorescence emission spectra. It shows an outstanding fluorometric sensing ability toward Al³⁺ ion, and the detection limit was measured to be 9.3 × 10^?8 mol L^?1 via fluorescence methods. Based on these interesting properties, a combinational logic circuit was constructed successfully.     

Anthrone-spirolactam and quinoline hybrid based sensor for selective fluorescent detection of Fe3+ ions

The synthesis of a novel, and highly selective Fe³⁺ ion sensor based on anthrone-spirolactam and its quinoline hybrid ligand is reported. The designed ligand displayed selective detection of Fe³⁺ ions with enhanced fluorescence emission. The complexation of Fe³⁺ ion led to a red shift of 32 nm from 420 nm to 452 nm, and a several fold increase in intensity with fluorescent green emission. The complexation (detection) of Fe³⁺ ions with ligand resulted in chelation enhanced fluorescence and intramolecular charge transfer through the inhibition of C=N isomerization. This hybrid sensor shows high sensitivity and selectivity, spontaneous response, and works on a wide pH range a minimum detection limit of 6.83 × 10⁻⁸ M. Importantly, the sensor works through the fluorescence turn-on mechanism that overcomes the paramagnetic effect of Fe³⁺ ions. The binding mechanism between the ligand and the Fe³⁺ ions was established from the Job's plot method, optical studies, Fourier transfor infrared spectroscopy, NMR titration, fluorescence life-time studies, and density functional theory optimization. The sensor displayed excellent results in the quantification of Fe³⁺ ions from real water samples. Furthermore, due to its biocompatibility nature, fluorescent spotting of Fe³⁺ ions in live cells revealed its bioimaging applications.     

A highly sensitive and selective fluorescent probe for trivalent aluminum ion based on rhodamine derivative in living cells

A rhodamine spirolactam derivative (1) is developed as a colormetric and fluorescent probe for trivalent aluminum ions (Al³⁺). It exhibits a highly sensitive “turn-on” fluorescent response toward Al³⁺ with a 70-fold fluorescence intensity enhancement under 2 equiv. of Al³⁺ added. The probe can be applied to the quantification of Al³⁺ with a linear range covering from 5.0 × 10⁻⁷ to 2.0 × 10⁻⁵ M and a detection limit of 4.0 × 10⁻⁸ M. Most importantly, the fluorescence changes of the probe are remarkably specific for Al³⁺ in the presence of other metal ions, which meet the selective requirements for practical application. Moreover, the experiment results show that the response behavior of 1 towards Al³⁺ is pH independent in neutral condition (pH 6.0–8.0) and the response of the probe is fast (response time less than 3 min). In addition, the proposed probe has been used to detect Al³⁺ in water samples and image Al³⁺ in living cells with satisfying results.     

Colorimetric detection of Fe3+/2+ and fluorescent detection of Al3+ in aqueous media: applications and DFT calculations

Abstract

A new multifunctional colorimetric and fluorescent chemosensor 1 for Fe^3+/2+ and Al³⁺ has been synthesized in the one-step procedure. The sensor 1 detected both Fe²⁺ and Fe³⁺ through the color change from yellow to brown and Al³⁺ via turn-on fluorescence. The binding stoichiometries of sensor 1 with Fe^3+/2+ and Al³⁺ were proposed to be 1:1 with the analyses of ESI-mass and Job plot. Importantly, the detection limits of 1 for Fe^3+/2+ (2.11 and 2.70 μM) and Al³⁺ (3.44 μM) were lower than the EPA guideline (5.37 μM) for Fe^3+/2+ and WHO guideline (7.41 μM) for Al³⁺. Compound 1 was used to quantify ferric species (Fe³⁺) in real samples. Moreover, the sensing processes for Fe^3+/2+ and Al³⁺ were proposed with the spectroscopic studies and theoretical calculations.     

A Novel Al(III)‐Selective Electrochemical Sensor Based on N,N′‐Bis(salicylidene)‐1,2‐phenylenediamine Complexes

A polyvinylchloride membrane sensor based on N,N′‐bis(salecylidene)‐1,2‐phenylenediamine (salophen) as membrane carrier was prepared and investigated as a Al³⁺‐selective electrode. The sensor exhibits a Nernstian response toward Al(III) over a wide concentration range (8.0×10^?7–3.0×10^?2 M), with a detection limit of 6.0×10^?7 M. The potentiometric response of the sensor is independent of the pH of the test solution in the pH range 3.2–4.5. The electrode possesses advantages of very fast response and high selectivity for Al³⁺ in comparison with alkali, alkaline earth and some heavy metal ions. The sensor was used as an indicator electrode, in the potentiometric titration of aluminum ion and in determination of Al³⁺ contents in drug, water and waste water samples.     

Bifunctional probe for Cu2+/Al3+ based on a diarylethene with a 4, 5-[bis-(5-ethylacetate-yl)-2-thienyl]-1H-imidazole unit

A new asymmetric perfluordiarylethene (1O) was synthesized using 4, 5-[bis-(5-ethylacetate-yl)-2-thienyl]-1H-imidazole as a functional group. 1O exhibited favorable reversible cyclization and cycloreversion reactions upon alternating irradiation with UV and visible light. Both of its open- and closed-ring isomers were found to be highly selective towards Cu²⁺ with significant absorption and color changes, which could be used as a ‘naked-eye’ colorimetric sensor for Cu²⁺ detection. Upon exposure to acid, its fluorescence dramatically enhanced by 14-fold with a color change from dark to bright cyan due to the formation of the protonated compound. Moreover, 1O showed obvious fluorescence “turn-on” signal response towards Al³⁺, and the detection limit for Al³⁺ was determined to be 4.8 × 10^?9 mol L^?1. Based on the fluorescence signals of 1O, a combinational stimuli logic circuit were designed by using the fluorescence intensity as the output signal with the inputs of lights, Al³⁺ and EDTA. Finally, 1O could be used as a biological probe for detecting intracellular Al³⁺ in a physiological environmental.     

Detection of Al3+ and Hg2+ ions with anthracene appended Schiff base and its reduced analogue

Abstract

Chemosensor 1 has been synthesized via a one-pot synthetic route incorporating anthracene and azomethine (HC═N—) units acting as signaling and binding units, respectively. Chemosensor 1 offered selective colorimetric and fluorometric response towards Al³⁺ and Hg²⁺ ions among other cations in CH₃OH. Solution of 1 in methanol exhibited a naked eye color transition from yellow to colorless on addition of Al³⁺ and Hg²⁺ ions. In case of emission experiments, non-fluorescent solution of 1 showed major enhancement in intensity giving blue fluorescence for both metal ions. The limits of detection were calculated to be 1.04 and 0.8 µM for Al³⁺ and Hg²⁺, respectively, using fluorescence titrations. Further, reduced form of Schiff base 1 (2) has also been synthesized in order to compare the importance of azomethine (HC═N—) and (H₂C—NH—) moieties in selective coordination. However, the reduced analogue 2 did not exhibit selective detection towards any of the ions.     

Optical detection of cyanide by palladium(II)-dithiazolopyridine probe at the parts per billion level

Abstract

The ensemble of 2,6-bis(2-chlorophenyl)dithiazolo[4,5-b:5',4'-e]pyridine 1 with Pd²⁺ ions (1?Pd²⁺) was prepared for the detection of cyanide ions (CN^¯) in 50% aqueous methanol. Among the tested metal ions, only Pd²⁺ sensitively induced the red shift of the absorption bands and the complete decrease of fluorescence emission. The detection limit toward Pd²⁺ was 2?ppb. The ensemble 1?Pd²⁺ selectively and rapidly detected a low concentration of cyanide ions by a colorimetric change (40?ppb) as well as a “turn-on” fluorescent response (5?ppb). Job’s plot revealed the complex formation with 1:1 stoichiometry. The binding and replacement mode of 1?Pd²⁺ and CN^¯ were also confirmed by ¹H NMR titrations and IR analysis. In general, a fast and selective recognition of CN^¯ is reported.     

1-[(2-Hydroxy-phenylimino)-methyl]-naphthalen-2-ol: application in detection and adsorption of aluminum ions

A novel “on–off” Al³⁺ ions fluorescence-enhanced sensor (E)-1-(((2-hydroxyphenyl) imino)methyl)naphthalen-2-ol (AH-2) and its hydrogel hybrid (PAMN) were synthesized. AH-2 showed excellent selectivity and ultrasensitive to Al³⁺ ions; the detection limit was 2.36?×?10^–9 M. The most plausible complexation mechanism was studied by ¹H NMR, FT-IR, HR-MS, Job’s plot and theoretical calculation. And, it was interesting that PAMN could adsorb Al³⁺ ions with a removal rate of over 99%, which also could easily be distinguished by the naked eye in UV lamp (365 nm). Before and after adsorption of Al³⁺ ions, the microstructures of PAMN were analyzed by scanning electron microscope and X-ray energy spectrometer. The silica gel detect plates prepared in this work could rapidly and conveniently detect Al³⁺ ions with a concentration greater than 5?×?10^–6 M (0.13 mg/L) in aqueous solution, and the detection concentration (0.13 mg/L) was lower than the national standard concentration of Al³⁺ ions (0.2 mg/L) in city tap water of china.

     

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.     

Linear Schiff-base fluorescence probe with aggregation-induced emission characteristics for Al detection and its application in live cell imaging

A simple Schiff-base derivative with salicylaldehyde moieties as fluorescent probe 1 was reported by aggregation-induced emission (AIE) characterization for the detection of metal ions. Spectral analysis revealed that probe 1 was highly selective and sensitive to Al³⁺. The probe 1 was also subject to minimal interference from other common competitive metal ions. The detection limit of Al³⁺ was 0.4 μM, which is considerably lower than the World Health Organization standard (7.41 μM), and the acceptable level of Al³⁺ (1.85 μM) in drinking water. The Job's plot and the results of ¹H-NMR and FT-IR analyses indicated that the binding stoichiometry ratio of probe 1 to Al³⁺ was 1:2. Probe 1 demonstrated a fluorescence-enhanced response upon binding with Al³⁺ based on AIE characterization. This response was due to the restricted molecular rotation and increased rigidity of the molecular assembly. Probe 1 exhibited good biocompatibility, and Al³⁺ was detected in live cells. Therefore, probe 1 is a promising fluorescence probe for Al³⁺ detection in the environment.     

New regioisomeric naphthol–thiazole based ‘turn-on’ fluorescent chemosensor for Al

Two new reactive and highly selective turn-on fluorescent chemosensors based on the position of ring annulation of the naphthalene–thiazole moiety for aluminum ions in ethanol, were synthesized and investigated. It was found that sensors 2 and 4 exhibited a remarkable enhancement of emission upon complexation with Al³⁺. A TD-B3LYP/6-31G(d,p) calculation was performed to characterize the nature of the fluorescence behavior of sensors 2 and 4 upon Al³⁺ complexation. The mechanism of fluorescence was based on the cation promoted hydrolysis of ester and subsequent complexation. The combination of experimental and computational analyses provides a more complete understanding of the molecular level origin of these types of unique photophysical properties.     

Fluorescence sensor using a molecularly imprinted polymer as a recognition receptor for the detection of aluminium ions in aqueous media

This paper describes the investigation of a molecularly imprinted polymer (MIP) as a sensing receptor for Al³⁺ ion detection by using an optical approach. Al³⁺ ion was adopted as the template molecule and 8-hydroxyquinoline sulfonic acid ligand as the fluorescence tag. The polymer was synthesised using acrylamide as monomer, 2-hydroxyethyl methacrylate as co-monomer and ethylene glycol dimethracylate as cross-linker. The free radical polymerisation was performed in methanol and initiated by 2,2′-azobisisobutyronitrile at 70 °C. The imprinted polymer was fluorometrically characterised using a fibre optic attachment in a self-designed flow-cell. NaF was used to leach the Al³⁺ ion from the MIP. The optimum pH for the rebinding of Al³⁺ ion with the leached polymer was found to be pH 5 and the fluorescence response was found to be stable within the buffer strength range of 0.05–0.10 M. The fluorescence intensity during Al³⁺ ion rebinding was inversely dependent on temperature, and a low interference response (<3%) toward metal ions except for Cu²⁺ and Zn²⁺ ions was observed. The polymer rebinding repeatability study conducted over 9 cycles with Al³⁺ ion (0.8×10⁻⁴ M) was found to give an RSD value of 2.82% with a standard deviation of 0.53. The dynamic range of the system was found to be linear up to 1.0×10⁻⁴ M Al³⁺ ion with a limit of detection of 3.62 μM.