A Highly Selective Chemosensor for Al(III) and Zn(II) and Its Coordination with Metal Ions

A pyrene-induced PET-based chemosensor for biologically important Zn(II) ions: application in test strips and live cell imaging studies

Cation and anion sensing is vital owing to their universal dispersion in ecosystems and biological functions. It has been shown that fluorescent receptors based on organic platforms are efficient for detecting a number of ions and have many advantages such as low cost, superior sensitivity and simplicity in installation. This study demonstrates the design and synthesis of a novel receptor (E)-3-[(3,5-di-tert-butyl-2-hydroxybenzylidene)amino]-2-(pyren-1-yl)-2,3-dihydroquinazolin-4(1H)-one (DTQ) for the rapid recognition of Zn(II) ions. DTQ exhibited a significant fluorometric "turn-on" characteristic towards Zn(II) at λmax 444 nm in aqueous acetonitrile by inhibiting the photo-induced electron transfer (PET) and -CN- process. The ESI-MS analysis and Job's plot experimental results confirmed stoichiometric 1 : 1 complex formation between DTQ and Zn(II). Fluorometric investigations revealed the detection limit and association constant of DTQ towards Zn(II), which were found to be 13.4 nM and 1.47 × 105 M-1, respectively. DTQ was employed to sense Zn(II) on low-cost test strips. The present research findings imply that DTQ can function as an effective sensor for Zn(II).

Naphthalene derived Schiff base as a reversible fluorogenic chemosensor for aluminium ions detection

Schiff base (HNPD) was achieved by reacting 2-hydroxy-1-naphthaldehyde with N-phenyl-o-phenylenediamine in enthanol medium. The spectroscopic analyses were done to establish the formation of Schiff base apparently. Further, synthesized Schiff base conjugate was successfully used as a fluorogenic chemosensor to detect aluminium ions (Al3+) with high fluorescence amplification among the other interfering various metal ions. The limit of detection of 0.0248 × 10-6 M and a binding constant of 6.19 × 103 M-1 were obtained by the receptor HNPD for Al3+ detection. A high influence of intramolecular charge transfer kinetics was established to realize the selective responsiveness towards Al3+ ions. Density functional theory approximation formulated the band energy modulation and localization and delocalization of electron density for the HNPD and Al3+ complexation. The developed sensor ultimately inspected on the real soil and water samples and ascertained the practical ability of Al3+ ions detection of HNPD chemosensor.

Turn-on detection of Al3+ and Zn2+ ions by a NSN donor probe: reversibility, logic gates and DFT calculations

An efficient dual functional naphthalene-derived Schiff base NpSb probe has been synthesised and evaluated for its fluorescence and chromogenic response towards metal ions. The NpSb probe was capable of selectively recognising Al3+ and Zn2+ ions when they were excited at the same wavelength in an aqueous organic solvent system. Almost non-fluorescent NpSb displayed a 'turn-on' fluorescence response when treated with Zn2+ (λem = 416 nm) and Al3+ (λem = 469 nm) ions due to the chelation-enhanced fluorescence (CHEF) effect. The limit of detection (LoD) values for Al3+ and Zn2+ have been determined to be 38.0 nM and 43.0 nM, respectively. The binding constants for Al3+ and Zn2+ were found to be 1.18 × 106 M-1 and 3.5 × 105 M-1, respectively. The NpSb also acted as a colorimetric sensor for Al3+ as the colour of the probe's solution turned to pale green from colourless upon Al3+ addition. The binding mechanism between NpSb and Zn2+/Al3+ was supported by the ESI-MS, Job's plot, NMR, and DFT studies. The reversibility experiments were carried out with an F- ion and EDTA with the development of corresponding logic gates. Moreover, NpSb could be applied to detect Al3+ ions in real samples such as tap water, distilled water and soil samples.

Synthesis and photophysical investigation of Schiff base as a Mg2+ and Zn2+ fluorescent chemosensor and its application

In view of the fluorescent switching properties and anti-fatigue properties of diarylethene, a diarylethene fluorescent chemosensor for the immediate detection of zinc ion (Zn²⁺ ) and magnesium ion (Mg²⁺ ) in acetonitrile was synthesized in this article. The structure of 1o was determined by performing spectroscopy and elemental analysis. The presence of Zn²⁺ or Mg²⁺ made the chemosensor 1o show an obvious "turn-on" fluorescent signal (bright yellow-green for Mg²⁺ and bright cyan for Zn²⁺ ). The fluorescent change caused by the 1:1 binding of 1o and Zn²⁺ or Mg²⁺ might be due to hindering the excited-state intramolecular proton transfer (ESIPT) process, which were bolstered by Benesi-Hildebrand analysis, Job's plot curves, proton nuclear magnetic resonance (¹ H-NMR) titration and mass spectrometry. The limits of detection were acquired from the standard curve plots for Mg²⁺ at 44.6 nM and for Zn²⁺ at 14 nM. Based on the fluorescent behaviors, a logic gate was constructed with the emission intensity at 528/518 nm as output signal, the ultraviolet-visible (UV-vis) lights, Mg²⁺ /Zn²⁺ and EDTA as input signals. Exogenous Zn²⁺ and Mg²⁺ fluorescent bioimaging were performed on Hela cells with 1o, indicating its potential application in biodiagnostic analysis. In particular, 1o was manufactured into test paper, and Zn²⁺ or Mg²⁺ can be conveniently, efficiently and qualitatively identified by the fluorescent color variation of the test strips.

Anthracene scaffold as highly selective chemosensor for Al3+ and its AIEE activity

Fluorescent chemosensor, 3-(Anthracen-2-yliminomethyl)-benzene-1,2-diol (ANB) has been synthesized by one-step condensation of 2-aminoanthracene and 2,3-dihydroxybenzaldehyde and characterized using ¹H-NMR, FT-IR and Mass spectroscopic techniques. The probe ANB was found to be an efficient 'turn-on' fluorescence chemosensor for the selective detection of Al³⁺ ion over other metal ions in an aqueous solution. The chemosensor exhibits ~ 27-fold enhancement of emission intensity in presence of Al³⁺ ion. Fluorescence quantum values for ANB and (Al³⁺-ANB)-complex are 0.004 and 0.097, respectively. In addition, the binding constant and the limit of detection were found to be 1.22 × 10⁴ M^-1 and 0.391 µM, respectively. The chemosensor ANB binds to Al³⁺ ions in 2:1 stoichiometric ratio which was supported by Job's plot, ¹H-NMR titration and florescence titration. Fluorescence reversibility of the sensor complex was well established by adding EDTA in the same condition and a molecular INHIBIT logic gate was fabricated using this reversible nature of the sensor complex. Additionally, the chemosensor ANB shows a novel aggregation-induced enhanced emission phenomenon, where the aggregate hydrosol of ANB shows enhance emission intensity.

A Simple Schiff Base as Fluorescent Probe for Detection of Al3+ in Aqueous Media and its Application in Cells Imaging

A novel fluorescence probe for the detection of Al³⁺ was developed based on methionine protected gold nanoclusters (Met-AuNCs). A fluorescent Schiff base (an aldimine) is formed between the aldehyde group of salicylaldehyde (SA) and the amino groups of Met on the AuNCs, and developed for selective detection of Al³⁺ in aqueous solution. Al³⁺ can strongly bind with the Schiff base ligands, accompanied by the blue-shift and an obvious fluorescence emission enhancement at 455 nm. The limits of detection (LODs) of the probe are 2 pmol L^-1 for Al³⁺. Moreover, the probe can successfully be used in fluorescence imaging of Al³⁺ in living cells (SHSY5Y cells), suggesting that the simple fluorescent probe has great potential use in biological imaging.

A naphthalene-based azo armed molecular framework for selective sensing of Al3+

A naphthalene-based azo armed molecular derivative was synthesized for sensing of Al3+ and cell imaging studies. The fluorescence enhancement is caused by restricted CN isomerization, CHEF on, and PET-off processes.

A novel double target fluorescence probe for Al3+/Mg2+ detection with distinctively different responses and its applications in cell imaging

The metal cations, Al³⁺ and Mg²⁺, could affect human health and cell biological processes. Their fast and selective detection using one probe remains a challenge. A novel fluorescence probe, N'-((1-hydroxynaphthalen-2-yl)methylene)isoquinoline-3-carbohydrazide (NHMI), was developed for selectively monitoring Al³⁺ and Mg²⁺. The probe NHMI showed a distinctive "turn-on" fluorescence signal towards Al³⁺ and Mg²⁺ (cyan for Al³⁺ with 2556-folds enhancement and yellow for Mg²⁺ with 88-folds enhancement), which is quite distinct from other metal cations and allows for naked-eye detection. This interesting response was attributed to the influence of PET, ESIPT process and CHEF effect, when Al³⁺ or Mg²⁺ chelated with NHMI. Furthermore, the fluorescence titration experiments manifested that the detection limit of probe NHMI for Al³⁺/Mg²⁺ was as low as 1.20 × 10^-8 M and 7.69 × 10^-8 M, respectively. The formed complexes NHMI-Al³⁺ and NHMI-Mg²⁺ were analyzed by Job's plot, ESI-MS, ¹H NMR and FT-IR. The coordination pockets and fluorescence mechanisms of two metal complexes were explored by density functional theory calculation. Moreover, NHMI showed low cytotoxicity and good cell permeability. Fluorescence bioimaging of Al³⁺/Mg²⁺ in MCF-7 cells with NHMI indicated its potential application in biological diagnostic analysis.

Discriminatory behavior of a rhodamine 6G decorated mesoporous silica based multiple cation sensor towards Cu2+ and Hg2+vis-à-vis Al3+, Cr3+ and Fe3+: selective removal of Cu2+ and Hg2+ from aqueous media

Selective identification of metal ions as well as their removal is possible when a sensing unit is anchored to a solid support. In this paper, functionalized mesoporous silica with a pendant rhodamine 6G moiety (R6FMS) has been obtained by successive grafting of an aldehyde derivative of bisphenol A followed by rhodamine 6G over a 3-aminopropyl anchored mesoporous silica framework. The materials have been characterized by powder X-ray diffraction, nitrogen sorption and electron microscopy studies, FT-IR and solid state MAS NMR spectral studies, and thermal analysis. In ethanol, the colorless silica material gives pink coloration in the presence of Al3+, Cr3+, Fe3+ and Cu2+ which is also clearly evident from the generation of an absorption peak at 525 nm. Upon excitation at 500 nm, the fluorescence intensity of the probe increases by 36-, 17-, 40- and 89-fold in the presence of Al3+, Cr3+, Fe3+ and Cu2+ ions, respectively. This suggests that R6FMS is a colorimetric and fluorescent chemosensor for these cations in ethanol. However, when the solvent is changed from ethanol to water, it becomes a selective chemosensor only for Cu2+ and Hg2+, by the generation of a pink color and strong fluorescence at ca. 550 nm, thereby discriminating the trivalent cations. Cations induce the opening of the spirolactam ring resulting in pink coloration and strong fluorescence. The quantum yield and lifetime of the probe have been increased considerably in the presence of these cations in ethanol as well as in aqueous media. The detection limit values for these cations range from 10-6 to 10-8 M. R6FMS has been used to remove Hg2+ and Cu2+ from their aqueous solution with a maximum adsorption capacity of 35 mg g-1 and 148 mg g-1 for Cu2+ and Hg2+, respectively.

ESIPT-AIE active Schiff base based on 2-(2'-hydroxyphenyl)benzo-thiazole applied as multi-functional fluorescent chemosensors

Three AIE (aggregation-induced emission)-ESIPT (excited-state intramolecular proton transfer) active 2-(2-hydroxyphenyl)benzothiazole derivatives, HL¹, HL² and HL³ with one, two and three rotatable phenyl groups, were obtained and characterized. Their AIE properties in THF/HEPES solution were investigated in detail. HL² shows the best AIE performance with 71-fold fluorescence enhancement, while HL³ only shows a 9-fold enhancement. With the AIE property, HL¹ and HL² could act as fluorescence chemosensors to detect Cu²⁺ ions via the "turn off" mode in THF/HEPES media. With the ESIPT property, HL¹ and HL² could also detect Zn²⁺ ions via the "turn on" mode in EtOH/HEPES media. During the detection process, both demonstrate rapid response and high contrast before and after the addition of metal ions. The species formed in the detection system were investigated. The results of X-ray single-crystal diffraction confirm that Zn²⁺ is coordinated with the oxygen atom and Schiff base nitrogen atom instead of the benzothiazole nitrogen atom in the tetrahedron geometry. Moreover, the chemosensors were successfully constructed into handy fluorescence test papers for Cu²⁺ and Zn²⁺ detection.

Solvent-Regulated Fluorimetric Differentiation of Al3+ and Zn2+ Using an AIE-Active Single Sensor

The absence of d-orbital electrons or presence of full-filled d-orbital electrons in metal ions is a well-known Achilles' heel problem for the detection of these metal ions by a simple UV-visible study. For this reason, detection of metal ions such as Al³⁺ with no d-orbital electrons or Zn²⁺ with filled d-orbital electrons is a challenging task. Herein, we report a 2-naphthol-based fluorescent probe [1-((E)-((E)-(5-bromo-2-hydroxybenzylidene)hydrazono)methyl)naphthalen-2-ol] (H₂L) that has been used to sense and discriminate Al³⁺ and Zn²⁺ via solvent regulation. The probe exhibits excellent selectivity and swift sensitivity toward Al³⁺ in MeOH-water (9:1, v/v) and toward Zn²⁺ in dimethyl sulfoxide (DMSO)-water (9:1, v/v) among various metal ions. The respective detection limit is found to be 9.78 and 3.65 μM. The sensing mechanism is attributed to multiple processes, viz., the inhibition of photo-induced electron transfer (PET) along with the introduction of chelation-enhanced emission (CHEF) and excited-state intramolecular proton transfer (ESIPT) inhibition, which are experimentally well verified by UV-vis absorption spectroscopy, emission spectroscopy, and NMR spectroscopy. The probe shows aggregation-induced emissive (AIE) response in ≥70% aqueous media as well as in the solid state. The experimental results are well corroborated by time-resolved photoluminescence (TRPL) and density functional theory (DFT) calculations. An advanced-level OR-AND-NOT logic gate has been constructed from a different chemical combinational input and emission output. The reversible recognition of both Al³⁺ in MeOH-water (9:1, v/v) and Zn²⁺ in DMSO-water (9:1, v/v) is also ascertained in the presence of Na₂EDTA, enabling the construction of a molecular memory device. The probe H₂L also detects intracellular Al³⁺/Zn²⁺ ions in Hela cells. Altogether, our fundamental findings will pave the way for designing and synthesis of unique chemosensors that could be used for cell imaging studies as well as constructing molecular logic gates.

A multi-binding site hydrazone-based chemosensor for Zn(ii) and Cd(ii): a new strategy for the detection of metal ions in aqueous media based on aggregation-induced emission

A multi-binding site chemosensor, N-(3-methoxy-2-hydroxybenzylidene)-3-hydroxy-2-naphthahydrazone (H₃L), with excited-state intramolecular proton transfer (ESIPT) behaviour was prepared and characterized. It possesses no aggregation-induced emission (AIE) characteristics but can detect Cd²⁺ and Zn²⁺ ions selectively in the "off-on" mode based on the AIE of their complexes in the media of THF/HEPES and THF/H₂O, respectively, which will provide a new strategy for target detection based on AIE. The detection limits of Zn²⁺ and Cd²⁺ were 9.85 × 10^-9 M and 1.27 × 10^-7 M, respectively. The aggregates of the complexes formed in the detection system were confirmed by DLS data and SEM images. The corresponding Zn²⁺ (1) and Cd²⁺ (2) complexes were prepared to investigate the response mechanism. Powder X-ray diffraction and single crystal X-ray diffraction proved that complex 1 is the species formed in the detection system. The chemosensor coordinates with the Cd²⁺ and Zn²⁺ ions in different formation and coordination modes, leading to the emission position of the aggregates at 560 and 645 nm, respectively, based on which Cd²⁺ ions were successfully differentiated from Zn²⁺ ions. Moreover, the detection of Cd²⁺ and Zn²⁺ ions was realized qualitatively via test paper and quantitatively in water.

Polyoxometalate based ionic crystal: dual applications in selective colorimetric sensor for hydrated ZnCl2 and antimicrobial activity

One-pot synthesis of POM-salt ([Himi]₄[SiMo₁₂O₄₀] (1)) was achieved by mixing silicomolybdic acid and imidazole in acidic conditions and characterized by FTIR, TGA, SEM, EDX, ICP-OES and XPS.

A squaraine-based fluorescence turn on chemosensor with ICT character for highly selective and sensitive detection of Al3+ in aqueous media and its application in living cell imaging

A novel and simple squaraine-based fluorescent chemosensor SQ-BH bearing the benzoylhydrazine moiety was developed for the highly sensitive and selective detection of Al³⁺ in methanol-water mixture. The chemosensing behaviors of SQ-BH and its binding interaction with Al³⁺ were explored by various spectroscopic analyses. The reversibility of Al³⁺ recognition process was investigated using EDTA. The results of experiments and DFT/TDDFT calculations revealed that the chemosensor SQ-BH obeyed a turn on mechanism which was associated with the inhibited photoinduced electron transfer (PET), the enhanced intramolecular charge transfer (ICT) and the activated chelation enhanced fluorescence (CHEF). Furthermore, the fluorescent chemosensor SQ-BH whose excellent biocompatibility was confirmed by a standard MTT assay could be used to detect Al³⁺ in living cells, indicating its potential application value in biological fields.

Rhodamine-based fluorescent probe for sequential detection of Al3+ ions and adenosine monophosphate in water

Organic nanoparticles (N1) were prepared by dispersing thiophene-conjugated rhodamine derivative 1 in a buffer solution (10 mM TRIS, pH 7.4, containing 1% DMSO, v/v). N1 selectively recognized Al³⁺ ions through the "OFF-ON" switching mechanism of the spirolactam ring in rhodamine. The resulting N1·Al³⁺ complex recognized the biologically important molecule adenosine monophosphate (AMP) through a cation displacement process with a detection limit of 2 nM. N1 was capable of determining the concentration of Al³⁺ ions in environmental and biological samples. Portable test strips of N1 were prepared for the recognition of Al³⁺ ions and AMP for practical uses. Furthermore, it was demonstrated that the N1·Al³⁺ complex facilitated real-time monitoring of AMP concentration in the hydrolysis of ATP and ADP.

Synthesis and cell imaging studies of an unusual “OFF–ON” fluorescent sensor containing a triazole unit for Al3+ detection via selective imine hydrolysis

A new fluorescent probe manipulated by the imine hydrolysis mechanism was engineered for monitoring Al³⁺ in cancerous and healthy cells.

A novel colorimetric-fluorescent probe for Al3+ and the resultant complex for F- and its applications in cell imaging

A novel quinoline-based Schiff-base probe QL had been synthesized, which could sequentially monitor Al³⁺ and F^- in MeOH-H₂O solution (v/v = 8/1, 0.01 M, HEPES buffer, pH = 7.3). The probe QL expressed a high selective and sensitive "OFF-ON-OFF" fluorescent response for Al³⁺ and F^- (excitation at 460 nm and emission at 530 nm) accompanying visible color changed, which was ascribed to intramolecular charge transfer (ICT) process and chelation-enhanced fluorescence (CHEF) mechanism. The binding stoichiometry of QL with Al³⁺ was 2:1 counting on Job's plot and HRMS, while F^- could pull Al³⁺ to depart from the complexation 2QL-Al³⁺ and released free QL. The limit of detections of probe QL for Al³⁺ and F^- ions were calculated to be 0.10 μM and 0.50 μM. The ¹H NMR experiments and density functional theory (DFT) calculations were carried out to further prove the binding mode between QL and Al³⁺. Furthermore, fluorescence imaging studies demonstrated that the probe QL was low cytotoxicity and could be applied to detect Al³⁺ and F^- in living PC12cells.

A novel fluorescent-colorimetric probe for Al3+ and Zn2+ ion detection with different response and applications in F- detection and cell imaging

A novel Schiff base fluorescence probe (HL) was synthesized by the condensation of salicylaldehyde and an 8-aminoquinoline derivative. This probe acts as a "turn-on" dual selectivity fluorescence probe for Zn²⁺ and Al³⁺ ions, providing different colors and detection limits (DL) of 11.5 and 23.5 nM, respectively. Moreover, when Zn²⁺ and Al³⁺ co-exist, HL exhibits a preference for Al³⁺ by displacing Zn²⁺ from the HL-Zn²⁺ complex, realizing a dual-channel signal output for Al³⁺. The HL-Al³⁺ system could further discern F^- by a "turn-off" fluorescence response with a DL of 86.0 nM. Furthermore, the probe HL was capable of monitoring intracellular Al³⁺, Zn²⁺ and F^- in living PC12 cells in vitro through fluorescence imaging, which proved its value in potential in vivo applications.

An imidazole derivative-based chemodosimeter for Zn2+ and Cu2+ ions through “ON–OFF–ON” switching with intracellular Zn2+ detection

Imidazole derivative-based chemodosimeter (HL) for selective detection of Zn²⁺ and Cu²⁺ metal ions and intracellular Zn²⁺ sensing.

Novel thiophene-based colorimetric and fluorescent turn-on sensor for highly sensitive and selective simultaneous detection of Al3+ and Zn2+ in water and food samples and its application in bioimaging

A novel bifunctional thiophene-based Schiff base TS as a colorimetric and fluorescent turn-on sensor for rapid and simultaneous detection of Al³⁺ and Zn²⁺ ions with high selectivity and sensitivity has been developed. The sensor shows remarkable fluorescence enhancement response for Al³⁺ and Zn²⁺ over a broad pH range with good anti-interference capability, which accompanied with an obvious color change easily detected by naked eyes. Sensor TS can detect as low as 3.7 × 10^-9 M for Al³⁺ and 3.0 × 10^-8 M for Zn²⁺, whereas respective association constants are 1.16 × 10⁴ M^-1 and 2.08 × 10⁴ M^-1. With the help of fluorescence titration and Job's plot, the stoichiometric ratio of TS with Al³⁺/Zn²⁺ was determined to be 1:1. The sensing mechanism of sensor TS with Al³⁺/Zn²⁺ based on the chelation-enhanced fluorescence (CHEF) was analyzed in detail through ¹H NMR titration, FTIR, HRMS and DFT studies. Moreover, sensor TS has been applied to the detection of Al³⁺ and Zn²⁺ in real environmental water and food samples as well as the filter paper-based test strips. Furthermore, sensor TS has good cell-permeability and can be used to selectively sense intracellular Al³⁺ and Zn²⁺ by bioimaging.