Simultaneous bioimaging recognition of Al3+ and Cu2+ in living-cell, and further detection of F- and S2- by a simple fluorogenic benzimidazole-based chemosensor

A Handy Chemical Sensor Based on Benzaldehyde and Imidazo[1,2-a]pyridine Mixture for Naked-eye Colorimetric and Fluorescent Detection of F. J Fluoresc 2023;33:2381-2390. [PMID: 37071230 DOI: 10.1007/s10895-023-03195-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Upon the Schiff base condensation reaction of imidazo[1,2-a]pyridine-2-carbohydrazide and 2,5-dihydroxybenzaldehyde, a bimodal colorimetric and fluorescent chemosensor 1o for assaying fluoride (F-) in DMSO was synthesized. The characterization of 1o structure was obtained by 1H NMR, 13C NMR and MS.The structure of 1o was characterized by 1H NMR, 13C NMR and MS. Under the presence of various anions, 1o could be applied for naked-eye and fluorescent detection of F- (naked eye: colorless to yellow; fluorescence: dark to green) and displayed promising performance, such as high selectivity and sensitivity, as well as a low detection limit. Upon calculation, the detection limit of chemosensor 1o for F- was 193.5 nM, which is well below the allowed maximum value of F- (1.5 mg/L) by WHO. As the intermolecular proton transfer mechanism induced "turn-on" fluorescent signal and naked-eye color change of F- to 1o through deprotonation effect, which was confirmed by Job's plot curve, mass spectrometry and 1H NMR titration. Alternatively, the chemosensor 1o can be effectively manufactured into test strips to detect fluoride in solid state, which is user-friendly with no additional equipment required.

The medicinal panorama of benzimidazoles and their scaffolds as anticancer and antithrombotic agents: A review

Nitrogen-containing heterocyclic scaffolds have become a prospective pharmacophore with therapeutic importance due to their biological similarities with natural and synthetic drugs. Among all nitrogen heterocyclic compounds, benzimidazoles and their derivatives are privileged molecules structurally akin to naturally available nucleotides, enabling them to intercommunicate with numerous biopolymers in biological systems. This reason enlightens modern researchers worldwide to assess their potential significance in the context of synthetic and biological chemistry. Therefore, it is crucial to merge the latest data with the prior documentation to apprehend the ongoing situation of the benzimidazole moiety in various therapeutic zones of research. The current work displays that the benzimidazole center is a versatile nucleus that offers the necessary data of synthetic alterations for pre-existing compounds to provide new scaffolds to resist numerous therapeutic sectors, including those associated with anticancer and antithrombosis. Due to the potential significance of benzimidazoles, this review aims to emphasize the latest innovations in synthesizing several other notable benzimidazole substrates and their significant pharmacological prospects for the future, including anticancer and antithrombosis.

A cyanobiphenyl-based fluorescent ''lighting-up'' sensor for highly selective and sensitive recognition of Al3+: Theoretical, practical and bioimaging studies

The recognition of toxic Al³⁺ in foods and biosystems has of great interest to researchers. Herein, a novel cyanobiphenyl-based chemosensor CATH (E)-N'-((4'-cyano-4-hydroxy-[1,1'-biphenyl]-3-yl)methylene)thiophene-2-carbohydrazide was fabricated and shown to recognize Al³⁺ in HEPES buffer:EtOH (90:10, v:v, pH = 7.4) by ''lighting-up'' fluorescence sensing. The CATH evidenced high sensitivity (LOD = 13.1 nM) and excellent selectivity to Al³⁺ over competing cations. The Job's plot, TOF-MS and theoretical computation studies were performed to probe the binding mechanism of Al³⁺ to CATH. Additionally; CATH was successfully utilized to practical applications and employed to recover of Al³⁺ from different food samples. More importantly, it was employed to intracellular Al³⁺ detection in living cells including THLE2 and HepG2.

Intramolecular dual hydrogen bonded fluorescent "turn-on" probe for Al3+ and HSO4- ions: Applications in real water samples and molecular keypad lock

Dual hydrogen bonded Schiff base containing unsymmetrical double proton transfer sites, one with imine bond (CN) and hydroxyl group (OH), and the other with benzimidazole and hydroxyl groups has been successfully synthesized. Probe 1 displayed intramolecular charge transfer and acts as a potential sensor for Al³⁺ and HSO₄^- ions. Probe 1 displayed two absorption peaks at 325 nm and 340 nm and an emission band at 435 nm upon excitation at 340 nm. Probe 1 behaves as a fluorescence "turn-on" chemosensor for both Al³⁺ and HSO₄^- ions in H₂O-CH₃OH solvent system. The proposed method allows the determination of Al³⁺ and HSO₄^- ions up to 39 nM and 23 nM at emission wavelength 385 nm and 390 nm, respectively. The binding behavior of probe 1 towards these ions is determined by the Job's plot method and ¹H NMR titrations. Probe 1 is used to construct a molecular keypad lock where the absorbance channel can be opened only in the presence of the correct sequence. Further, it is used for the quantitative determination of HSO₄^- ion in different real-field water samples.

Comprehensive Insights into Medicinal Research on Imidazole-Based Supramolecular Complexes

The electron-rich five-membered aromatic aza-heterocyclic imidazole, which contains two nitrogen atoms, is an important functional fragment widely present in a large number of biomolecules and medicinal drugs; its unique structure is beneficial to easily bind with various inorganic or organic ions and molecules through noncovalent interactions to form a variety of supramolecular complexes with broad medicinal potential, which is being paid an increasing amount of attention regarding more and more contributions to imidazole-based supramolecular complexes for possible medicinal application. This work gives systematical and comprehensive insights into medicinal research on imidazole-based supramolecular complexes, including anticancer, antibacterial, antifungal, antiparasitic, antidiabetic, antihypertensive, and anti-inflammatory aspects as well as ion receptors, imaging agents, and pathologic probes. The new trend of the foreseeable research in the near future toward imidazole-based supramolecular medicinal chemistry is also prospected. It is hoped that this work provides beneficial help for the rational design of imidazole-based drug molecules and supramolecular medicinal agents and more effective diagnostic agents and pathological probes.

Spectroscopic and Density Functional Studies on the Interaction of a Naphthalene Derivative with Anions

This article highlights the investigation of anion interactions and recognition abilities of naphthalene derivative, [(E)-1-(((4-nitrophenyl)imino)methyl)naphthalen-2-ol], (NIMO) by UV-visible spectroscopically and colorimetrically. NIMO shows selective recognition of F^- ions colorimetrically, and a visual color change from yellow to pink is observed by the naked eye. The F^- ions recognition is fully reversible in the presence of HSO₄^- ions. The limit of F^- ions detection by NIMO could be possible down to 0.033 ppm-level. A paper strips-based test kit has been demonstrated to detect F^- ions selectively by the naked eye, and a smartphone-based method for real sample analysis in the non-aqueous medium has also been demostrated. Spectroscopic behavior is well supported by pK_a value calculation and DFT analysis, to find a correlation with receptor analyte interaction. The optical response of NIMO towards the accumulation of F^- ions and, subsequently, HSO₄^- ions as chemical inputs provides an opportunity to construct INH and IMP molecular logic gates.

The detection of multiple analytes by using visual colorimetric and fluorometric multimodal chemosensor based on the azo dye

In recent decades, researchers have conducted in-depth studies of the design and synthesis of colorimetric/fluorometric probes and the application of such probes to biological and practical samples. The multifunctional colorimetric and fluorescent azo benzene-based probe (4′-hydroxyl-2,4-diaminoazobenzene, MP) was designed to detect Al³⁺, Fe³⁺, Cu²⁺ and F¯. Based on the distinct redshift of the absorption band and a significant color change (yellow → purple), MP was utilized for both naked-eyed and quantitative detection of Al³⁺ and Fe³⁺ after formation of the 1:1 complex. Test paper coated with MP and used in conjunction with a cell phone was used for colorimetric detection of Al³⁺ and Fe³⁺ ions (20 μM–2.0 mM) in water samples through naked-eye and digital image colorimetry. The “MP-Fe³⁺” coordination shift that occurs in the presence of the competitive ligand F¯ was used in the colorimetric measurement of F¯ in toothpaste. In the presence of Cu²⁺ ion, the non-emissive MP has transformed into fluorescent benzotriazole product PMP (Φ = 0.53) through the bimolecular rate-limiting step, and the second-order rate constant k is calculated as 31 ± 2 M⁻¹ s⁻¹. MP exhibits a “turn-on” fluorescence response in the presence of Cu²⁺ that is greater than its response in the presence of competitive species such as Fe³⁺, Al³⁺, Co²⁺, Fe²⁺, Zn²⁺, Cd²⁺, Mg²⁺, Mn²⁺, Ni²⁺ and Ag⁺. MP was shown to have low toxicity to living HeLa cells and to present good imaging characteristics for tracking of Cu²⁺ in vivo.

Turn on Fluorescence Sensing of Zn2+ Based on Fused Isoindole-Imidazole Scaffold

Optical chemosensors caused a revolution in the field of sensing due to their high specificity, sensitivity, and fast detection features. Imidazole derivatives have offered promising features in the literature as they bear suitable donor/acceptor groups for the selective analytes in the skeleton. In this work, an isoindole-imidazole containing a Schiff base chemosensor (1-{3-[(2-Diethylamino-ethylimino)-methyl]-2-hydroxy-5-methyl-phenyl}-2H-imidazo[5,1-a]isoindole-3,5-dione) was designed and synthesized. The complete sensing phenomena have been investigated by means of UV-Vis, fluorescence, lifetime measurement, FT-IR, NMR and ESI-MS spectroscopic techniques. The optical properties of the synthesized ligand were investigated in 3:7 HEPES buffer:DMSO medium and found to be highly selective and sensitive toward Zn²⁺ ion through a fluorescence turn-on response with detection limit of 0.073 μm. Furthermore, this response is effective in gel form also. The competition studies reveal that the response of the probe for Zn²⁺ ion is unaffected by other relevant metal ions. The stoichiometric binding study was performed utilizing Job’s method which indicated a 1:1 sensor–Zn²⁺ ensemble. Computational calculations were performed to pinpoint the mechanism of sensing.

Real time sensor for Fe3+, Al3+, Cu2+ & PPi through quadruple mechanistic pathways using a novel dipodal quinoline-based molecular probe

A quinoline-based small molecular probe, H₂L was designed, synthesized and characterized by different spectroscopic methods. It was utilized as a multi-responsive probe for the detection of Fe³⁺, Al³⁺, Cu²⁺ and PPi. It showed very selective instant turn-on fluorimetric response towards Fe³⁺and Al³⁺ with a detection limit in nanomolar range. Solutions of H₂L containing Fe³⁺ or Al³⁺ could sequentially sense PPi by a turn-off mechanism. Also, H₂L could determine the presence of Cu²⁺ very selectively among a series of other metal ions by a sharp change in colour. Detection of Cu²⁺ through colorimetry was further investigated by systematic UV-Vis studies and the potential of H₂L to act as a potential colorimetric sensor for Cu²⁺ was suitably established. Filter-paper strip experiments were conducted to demonstrate the practical utility of the proposed sensor. Potential applications of H₂L as a sensor for pH in the acidic range has also been explored.

A reversible and efficient probe for dual mode recognition of Al3+ and Cu2+ with logic gate behaviour: Crystal structure, theoretical and in-vivo bio-imaging investigations

This work presents the synthesis, characterization, crystal structure and spectroscopic investigations of isophthalohydrazide based probe. Among various tested metal ions, the probe selectively detects Al³⁺ and Cu²⁺ in aqueous ethanol via fluorometric and colorimetric methods, respectively. It displays a fluorescence "turn-on" response with Al³⁺ and visual colour change from colourless to yellow with Cu²⁺. Sensing mechanism is explored with UV-Vis, fluorescence spectroscopy and ¹H NMR titration, and confirmed with computational results. Suppression of CN isomerization and photo-induced electron transfer (PET) along with chelation enhanced fluorescence emission (CHEF) result in "turn-on" fluorescence with Al³⁺ while ligand to metal charge transfer (LMCT) accounts for visual colour change with Cu²⁺. Job's plot and HRMS confirm 1:2 (L:M) stoichiometry. The probe also exhibits efficient reversibility and reproducibility with EDTA which are successfully mimicked with combinatorial logic gate and truth table. Additionally, solid state applications and bio-imaging investigation on gut tissue of Drosophila 3rd instar larvae are performed.

Interfacially Super-Assembled Benzimidazole Derivative-Based Mesoporous Silica Nanoprobe for Sensitive Copper (II) Detection and Biosensing in Living Cells

Mesoporous silica nanoparticles (MSNs) functionalized with benzimidazole-derived fluorescent molecules (DHBM) are fabricated via a feasible interfacial superassembly strategy for the highly sensitive and selective detection of Cu²⁺ . DHBM-MSN exhibits an obvious quenching effect on Cu²⁺ in aqueous solutions, and the detection limit can be as low as 7.69×10^-8  M. The DHBM-MSN solid-state sensor has good recyclability, and the silica framework can simultaneously improve the photostability of DHBM. Two mesoporous silica nanoparticles with different morphologies were specially designed to verify that nanocarriers with different morphologies do not affect the specific detectionability. The detection mechanism of the fluorescent probe was systematically elucidated by combining experimental results and density function theory calculations. Moreover, the detection system was successfully applied to detect Cu²⁺ in bovine serum, juice, and live cells. These results indicate that the DHBM-MSN fluorescent sensor holds great potential in practical and biomedical applications.

Performance of 2-Hydroxy-1-Naphthaldehyde-2-Amino Thiazole as a Highly Selective Turn-on Fluorescent Chemosensor for Al(III) Ions Detection and Biological Applications

The thiazole based Schiff base 2-hydroxy-1-naphthaldehyde-2-amino thiazole (receptor1) was synthesized through a single step process and characterized by spectroscopic and analytical techniques. The cation detecting ability of the receptor1 was explored by fluorescent spectroscopic methods. The receptor1 has recognized Al3+ ions by a turn-on process over a panel of other potentially competing metal ions. The binding constant of receptor1 with Al3+ was found to be 8.27 × 103 M-1. Computational studies Density Functional Theory (DFT) and Time-dependent Density Functional Theory (TD-DFT) were performed to provide detailed information on electronic states and photophysical property of receptor1 and receptor1-Al3+ ions. MTT (3-(4,5-dimethyl thiazole-2-yl)-2,5-diphenyl tetrazolium bromide) assay and bioimaging applications were made on breast carcinoma cells in humans.

New thiophene hydrazide dual-functional chemosensor: Colorimetric sensor for Cu2+ & fluorescent sensor for Al3

A new thiophene hydrazide derivative TSB was synthesized and utilized as naked-eye colorimetric sensor for Cu²⁺ by the color changed from colorless to yellow as well as green fluorescent turn on sensor for Al³⁺ in DMSO/H₂O (1/1, V/V) solution. The dual-functional chemosensor TSB for Cu²⁺/Al³⁺ sensing displayed excellent properties of special selectivity, superior sensitivity, outstanding anti-interference performance, instantaneous response, wide pH working range and good reversibility. The detection limits of TSB for Cu²⁺/Al³⁺ were determined as low as 46.5 nM and 32.7 nM, respectively. The 1:1 binding mode of TSB with Cu²⁺/Al³⁺ was proved by spectrometric titrations, Job's plots, FTIR, ¹H NMR and HRMS analysis. Moreover, chemosensor TSB was successfully utilized for detection of Cu²⁺ and Al³⁺ in real environmental water and food samples with high reliability, demonstrating its practical applicability.

Pyridinyl Conjugate of UiO-66-NH2 as Chemosensor for the Sequential Detection of Iron and Pyrophosphate Ion in Aqueous Media

A new chemosensor UiO-66-N-Py (Py = 2-methinepyridine, N = imine nitrogen) based on isoreticular UiO-66 (University of Oslo) Metal–Organic Framework (MOF) containing 2-methinepyridine functionalized organic linker was solvothermally synthesized and characterized. This UiO-66-N-Py was very selective and sensitive for detecting the Fe3+ ion and sequential detection of the pyrophosphate (PPi) anion. The limits of detection for the Fe3+ ion and PPi were calculated to be 10 ppb (0.19 μM) and 50 ppb (0.3 μM), respectively. The quenching constant Ksv for Fe3+ and the binding constant for PPi were 1.4 × 105 M−1 and 1.7 × 105 M−1, respectively. The functionalization of UiO-66-NH2 with 2-methinepyridine enhanced its fluorescence emission properties and introduced more binding sites for the analytes. We additionally studied the interaction of the sensor and the analytes with Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). This chemosensor also demonstrated a regenerative emission property without loss in the detection ability for six consecutive cycles.

Selective Sensing of Cu2+ and Fe3+ Ions with Vis-Excitation using Fluorescent Eu3+-Induced Aggregates of Polysaccharides (EIAP) in Mammalian Cells and Aqueous Systems

Fluorescent lanthanide complexes have favorable features for fluorescence-based sensors compared to organic fluorophores and quantum dots. They exhibit very long fluorescence lifetimes, sharp emission bands, and stability with respect to photo-bleaching, without blinking. However, these complexes are usually hydrophobic, and many are excited by UV light, making them hazardous and incompatible with aqueous environments and biological samples. In this work, the strong fluorescent Eu³⁺-induced aggregates of polysaccharides (EIAP) was used to improve their aqueous solubility, and to tune the appropriate excitation wavelength in the visible range for avoiding toxicity of UV light in biological applications. The complexes exhibit bright fluorescence with an excitation maximum in the visible range, near 405 nm. EIAP 3 also exhibit rapid quenching response in the presence of transition metal ions. This enables the detection of Cu²⁺ and Fe³⁺ below 1 ppm. The reverse of quenching response of copper by the addition of a chelating agent makes it possible to recover the fluorescence property. Successfully, the EIAP exhibit cytocompatibility with mammalian cells. Thus, these new polysaccharide-based complexes have the potential for rapid, sensitive and selective metal ion sensors for the environmental systems.

Synthesis, biological evaluation and model membrane studies on metal complexes containing aromatic N,O-chelate ligands

Novel lanthanide (Ln) compounds [Ln(L)₂]Cl^.xH₂O (Ln = La³⁺, Ce³⁺, Sm³⁺) containing aromatic N,O-chelate ligands [HL1 = 4-amino-2-(1H-benzimidazol-2-yl)phenol; HL2 = 5-amino-2-(1H-benzimidazol-2-yl)phenol] have been synthesized and structurally characterized by elemental analysis, NMR and IR spectroscopy, molar conductance measurements, and mass spectrometry (MS). The spectroscopic data suggested that the benzimidazolyl-phenol ligands act as N,O-chelate ligands through the iminic nitrogen and phenolic oxygen atoms. Elemental analysis indicated that lanthanide compounds were formed in a 1:2 stoichiometry (metal:ligand). In vitro biological evaluation was carried out using these complexes, exhibiting moderate cytotoxicity against six different human tumor cell lines (U251, human glioblastoma; HCT-15, colorectal carcinoma; MCF-7, breast epithelial adenocarcinoma; PC-3, prostate cancer; K562, myelogenous leukemia; SKLU-1, lung carcinoma) and lower toxicity against a non-cancerous cell line (COS-7, primate kidney). In addition, the antibacterial activity of the compounds was assessed against two gram-positive strains (Staphylococcus aureus ATCC 25923, Listeria monocytogenes ATCC 19115) and two gram-negative strains (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27583) using the microdilution method. The results obtained show that the metal complexes exhibit higher biological activity than the free ligands, confirming a synergistic effect. Further benzimidazolyl-phenol derivatives were explored for the detection of bacteria using fluorescence imaging studies. Interestingly, the fluorescent properties of these compounds make them potential candidates to monitor the morphology of bacteria at different compound concentrations. Hence, the interaction of the ligand and complexes with model membranes mimicking those of bacteria was studied by using differential scanning calorimetry (DSC) and molecular dynamics (MD), showing that both compounds decreased the enthalpy of transition in two model membranes as the concentration of the compounds increased. In addition, the main transition temperature was slightly reduced as a result of these interactions.

Hairy Fluorescent Nanospheres Based on Polyelectrolyte Brush for Highly Sensitive Determination of Cu(II)

Currently, it is an ongoing challenge to develop fluorescent nanosphere detectors that are uniform, non-toxic, stable and bearing a large number of functional groups on the surface for further applications in a variety of fields. Here, we have synthesized hairy nanospheres (HNs) with different particle sizes and a content range of carboxyl groups from 4 mmol/g to 9 mmol/g. Based on this, hairy fluorescent nanospheres (HFNs) were prepared by the traditional coupling method (TCM) or adsorption-induced coupling method (ACM). By comparison, it was found that high brightness HFNs are fabricated based on HNs with poly (acrylic acid) brushes on the surface via ACM. The fluorescence intensity of hairy fluorescent nanospheres could be controlled by tuning the content of 5-aminofluorescein (5-AF) or the carboxyl groups of HNs easily. The carboxyl content of the HFNs could be as high as 8 mmol/g for further applications. The obtained HFNs are used for the detection of heavy metal ions in environmental pollution. Among various other metal ions, the response to Cu (II) is more obvious. We demonstrated that HFNs can serve as a selective probe and for the separation and determination of Cu(II) ions with a linear range of 0-0.5 μM and a low detection limit of 64 nM.

Fluorescent schiff base probes for sequential detection of Al3+ and F- and cell imaging applications

Two novel Schiff-base fluorescent probers SQ and NQ based on 8-hydroxyquinoline moiety were designed and synthesized. The both probes were capable of binding with Al³⁺ by naked eye detection to produce a significant fluorescence enhancement response with a detection limit of 1.48 × 10^-8 and 4.23 × 10^-8 M, respectively. At the same time, the formed complexes SQ-Al³⁺ and NQ-Al³⁺ could sequentially detect F^-, and the detection limits of F^- were determined to be 1.64 × 10^-7 and 3.58 × 10^-8 M, respectively. The "off-on-off" fluorescence response process demonstrated that the binding were reversible. The probes were further successfully utilized to detect Al³⁺ and F^- in vitro PC12 cells.

Pyrene derivative-functionalized mesoporous silica-Cu2+ hybrid ensemble for fluorescence "turn-on" detection of H2S and logic gate application in aqueous media

The ensemble system PyH-SBA-15-Cu²⁺ was obtained via coordination interaction of pyrene derivative-functionalized mesoporous SBA-15 and Cu²⁺, and applied for the selective and sensitive detection of H₂S over pH 6.0-12.0 in aqueous media. The sensing strategy was designed on the basis of the H₂S-induced dissolution of Cu²⁺ from PyH-SBA-15-Cu²⁺. Cu²⁺ has good binding affinity to N atoms in PyH-SBA-15; therefore, the organic-inorganic hybrid ensemble PyH-SBA-15-Cu²⁺ was formed, which is nonfluorescent in aqueous solution because of the Cu²⁺-promoted emission quenching of PyH-SBA-15. The addition of H₂S induces the dissolution of PyH-SBA-15-Cu²⁺ by the formation of stable CuS, thereby producing fluorescence revival of PyH-SBA-15. The correlative "turn-on" fluorescence signals of this ensemble system are linearly proportional to [H₂S] in the concentration region of 0-1.0 × 10^-4 M, showing a low detection limit of 3.7 × 10^-7 M. Other common anions do not induce distinct fluorescence changes. When using the fluorescence intensity signal changes of PyH-SBA-15 as outputs and Cu²⁺ and S^2- as inputs, PyH-SBA-15 can act as an XNOR logic gate.

A dual fluorescence probe for Zn2+ and Al3+ through differentially response and bioimaging in living cells

A novel Schiff base fluorescent probe 7-Hydroxy-8-(((2-(hydroxymethyl)quinolin-8-yl)imino)methyl)-coumarin (XL) consist of formylcoumarin and aminoquinoline moieties was synthesized for dual detection of Zn²⁺ and Al³⁺ ions. Probe XL exhibited high selective and sensitive response towards Zn²⁺ and Al³⁺ ions through different color changes and significant fluorescence turn-on response (270 fold higher for Zn²⁺ and 230 fold higher for Al³⁺) in MeOH-H₂O (4/1, v/v) over other cations, with detection limits (LOD) as low as 3.75 × 10^-8 and 1.14 × 10^-8 M, respectively. Moreover, probe XL exhibited preferential selectivity for Al³⁺ through displacing Zn²⁺ from the XL-Zn²⁺ complex by ligand-to-ligand transfer process. The binding mechanism of intramolecular charge transfer (ICT) were proposed from fluorescence and UV-vis titrations, Job's plot, ¹H NMR titration, HRMS and DFT calculations. The probe was proven to be suitable for actual samples detection of Zn²⁺ and Al³⁺ ions. The complex XL-Zn²⁺ and XL-Al³⁺ exhibited dramatic fluorescent "turn-off" properties for PPi and PPi/F^- respectively through snatching metal ions and released free XL. Moreover, probe XL showed low biotoxicity and sequentially "off-on-off" fluorescent bio-imaging of Zn²⁺/Al³⁺ and PPi/F^- in PC12 cells.

Novel benzimidazole-based conjugated polyelectrolytes: synthesis, solution photophysics and fluorescent sensing of metal ions

Two benzimidazole-based conjugated polyelectrolytes (+)-PPBIPV and (-)-PPBIPV which have opposite charges on their side chains were synthesized via Heck coupling reaction and characterized by 1H-NMR, UV-vis and PL spectroscopy. These two polyelectrolytes are both consisted of benzimidazole derivatives and phenylenevinylene units. The absorption and emission spectra reveal that the polymers both have solvent-dependency and concentration-dependency, and they exhibit aggregation effect in aqueous solution. In the respect of ion detection, the aqueous solution of (+)-PPBIPV has excellent selectivity and sensitivity for Fe3+. Moreover, Pd2+ can almost completely quench the fluorescence of (+)-PPBIPV in methanol solution, and its quenching constant KSV is 5.93×104 M-1. For (-)-PPBIPV, Sn2+ can double the fluorescence intensity of its aqueous solution, while (-)-PPBIPV has good identification for Fe3+ in methanol with a KSV = 3.44×105 M-1. Hence, two polyelectrolytes have considerable potential to become effective fluorescent sensing materials for some specific metal ions. All of the stoichiometric relationships between metal ions and conjugated polyelectrolytes were calculated using Benesi-Hildebrand equation.

A highly selective fluorescent probe for Al3+ based on bis(2-hydroxy-1-naphthaldehyde) oxaloyldihydrazone with aggregation-induced emission enhancement and gel properties

An efficient fluorescent probe, bis(2-hydroxy-1-naphthaldehyde) oxaloyldihydrazone (1), has been prepared for the selective sensing of Al³⁺ over other common metal ions in water-containing media. The 1:1 stoichiometry of 1 and Al³⁺ was determined from Job's plot and Benesti-Hildebrand plot. The binding constant was observed as 1.6×10⁵M^-1, and the limit of detection was found to be 0.36μM, which was far below the drinking water restriction of Al³⁺ by EPA (the maximum allowable value is 7.4μM). In addition, the inherent AIEE features of 1 were observed upon addition of water to DMSO solution due to the restriction of the intramolecular motion, which makes the molecular conformations rigid and planar. Moreover, 1 could act as a novel gelator to form thermo-reversible supramolecular organogel with significant green emission in DMSO-H₂O (v/v, 9:1) solution.

A hydrazide organogelator for fluoride sensing with hyperchromicity and gel-to-sol transition

Sensing of fluoride in a solvent is highly required in healthcare and environmental rehabilitation. Among the various sensing methods, optical sensing has attracted significant research interest because it can conveniently recognize fluoride. Herein, a low molecular weight organogelator, N′1,N′6-bis(3-(1-pyrrolyl)propanoyl) hexanedihydrazide (DPH), containing a central butyl chain conjugated to two pyrrole rings through hydrazide groups, was used for optical sensing of fluoride in the forms of both solution and organogel. Association of fluoride with the –NH moiety of the hydrazide group endowed the DPH solution in dimethylformamide with a hyperchromicity under 350 nm. Exploiting the UV absorptivity, the DPH solution was examined as a chemosensor, displaying good selectivity toward fluoride among various anions and moderate sensitivity with a detection limit of 0.49 μM. The practical use of the DPH solution was demonstrated for fluoride sensing in toothpaste. Binding of fluoride also changed the molecular interactions of the DPH organogel, resulting in a phase transition from gel to sol. This gel-to-sol transition enabled the sensing of fluoride by the naked eye.

A low-molecular-weight organogelator containing hydrazide groups, DPH, exhibited considerable selectivity and sensitivity for fluoride. The optical sensing of fluoride was demonstrated with the systematic study on the sensing mechanism.

A novel ratiometric and reversible fluorescent probe based on naphthalimide for the detection of Al3+ and pH with excellent selectivity

A novel ratiometric and reversible fluorescence probe was designed and synthesized. The fluorescent probe recognizes Al³⁺ to cause a blue shift in the fluorescence emission spectrum. Fluorescence probe can be used as a sensor to detect Al³⁺ in living cells and Zebra fishes. The probe can detect the pH value when the alkalinity range was 8–10.

Double Schiff base from thiophene-2,5-dicarboxylic acid as an “off–on–off” fluorescence sensor for the sequential detection of In3+ and PPi

A double Schiff base T as acceptor for metal ions derived from thiophene-2,5-dicarboxylic acid was designed and synthesized, and showed a high selectivity for In³⁺ in a DMF/H₂O buffer solution.

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.

Synthesis of methionine methyl ester-modified coumarin as the fluorescent-colorimetric chemosensor for selective detection Cu2+ with application in molecular logic gate

A methionine methyl ester-modified coumarin derivative was designed and synthesized, which could discriminate Cu²⁺ from other metal ions in HEPES buffer (10 mM, pH 7.4)/CH₃CN (40:60, V/V). The detection limit of WM toward Cu²⁺ was 1.84 × 10^-7 M, which was lower than the concentration of Cu²⁺ in drinking water suggested by WHO and EPA. And the proposed coordination mode exhibiting the interaction between WM and Cu²⁺ was studied by UV-Vis, fluorescence spectrum, ESI-MS and FT-IR. Based on the fluorescent reversibility of WM, WM was considered as a molecular logic gate and molecular keypad lock. In addition, the test strips and the silica gel plates prepared from the solution of WM also demonstrate the favorable selectivity toward Cu²⁺.

Aggregation-Induced Emission-Active Hydrazide-Based Probe: Selective Sensing of Al3+, HF2 -, and Nitro Explosives

(E)-N'-((2-Hydroxynaphthalen-1-yl)methylene)picolinohydrazide (H-PNAP) shows aggregation-induced emission (AIE) strictly in a 90% water/MeOH (v/v) mixture at 540 nm, and the solid-state emission is blue-shifted to 509 nm upon excitation at 400 nm. The AIE activity of H-PNAP is selectively quenched by 2,4,6-trinitrophenol (TNP) and 2,4-dinitrophenol (DNP) out of different nitroaromatic compounds with a limit of detection (LOD) of 7.79 × 10-7 and 9.08 × 10-7 M, respectively. The probe is nonemissive in aqueous medium (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, HEPES buffer, pH 7.2); however, it shows a strong emission to Al3+ (λem, 490 nm) in the presence of 17 other biological metal ions, and the LOD is 2.09 nM which is far below the WHO recommended value (7.41 mM). The emission of the [Al(PNAP)(NO3)2] complex is quenched by HF2 - (F- and PO4 3- are weak quencher), and the LOD is as low as 15 nM. The probable mechanism of the sensing feature of the probe has been authenticated by 1H nuclear magnetic resonance titration, mass spectrometry, Fourier transform infrared spectroscopy, Benesi-Hildebrand plot, and Job's plot in each case. The probe has some practical applications such as recovery of Al3+ from the drinking water sample, construction of the INHIBIT logic gate, and detection kits for Al3+ and TNP/DNP by simple paper test strips. The probe, H-PNAP, has successfully been applied to the detection of intracellular Al3+ and HF2 - ions in the human breast cancer cell, MDA-MB-468.

AIE active salicylaldehyde-based hydrazone: A novel single-molecule multianalyte (Al3+ or Cu2+) sensor in different solvents

A simple asymmetric hydrazone 1 based on salicylaldehyde was designed and prepared, and exhibited an evident aggregation-induced emission (AIE) at a long wavelength of 570 nm in aqueous medium. Probe 1 can selectively sense Al³⁺ in CH₃OH solution through the chelation-enhanced fluorescence mechanism and also recognize Cu²⁺ via fluorescence quenching in H₂O solution through the Cu²⁺-induced assembly of aggregates. In addition, the probe can be applied for detecting Cu²⁺ in biological samples.

A selective diaminomaleonitrile-based dual channel emissive probe for Al3+ and its application in living cell imaging

A selective diaminomaleonitrile-based fluorescent probe for Al³⁺(L) has been synthesized and characterized. The sensing behavior of L towards different metal ions was investigated by fluorescent spectra and competition experiment. The results showed that L exhibited a dual channel emission (λ_em 522 & 558 nm) with yellow fluorescence in the presence of Al³⁺ over other metal ions in EtOH solution. The probe L was bound to Al³⁺ in a 1:2 stoichiometric manner as supported by Job's plot analysis. The binding constant was 9.55 × 10⁸ M^-2 with the detection limit of 10.3 nM. The turn-on response was attributed to the inhibition of PET and CN isomerization after binding with Al³⁺ while the dual emissions were due to ESIPT and ICT processes. In addition, the application of L for imaging Al³⁺ in living Hela cells was achieved.

A Highly Selective Fluorescence "Turn on" and Absorbance-Ratiometric Detection of Al3+ in Totally H2O and its Application in Test Paper

A novel naphthalene based fluorescence probe NBDH was designed and synthesized. Probe NBDH exhibited highly selective and sensitive responses towards Al³⁺ in HEPES-NaOH buffer solution (pH = 7.4). In addition, the detection of NBDH to Al³⁺ could be achieved through dual channels embodied in significant fluorescent turn-on signal and ratiometric absorbance response. The stoichiometry ratio of NBDH-Al³⁺ was 1:1 by fluorescence job' plot and binging mechanism was further varified by the FT-IR, NMR titration and HRMS. Furthermore, NBDH was achieved in real sample detection, and a series of color test paper were developed for visual detecting Al³⁺ ions.

A reversible and highly selective two-photon fluorescent "on-off-on" probe for biological Cu2+ detection

A two-photon active probe for physiological copper (Cu2+) detection is expected to play an important role in monitoring biological metabolism. Herein, a novel Schiff base derivative (E)-2,2'-((4-((4-(diethylamino)-2-hydroxybenzylidene)amino)phenyl)azanediyl)bis(ethan-1-ol) (L) with remarkable two-photon activity was developed and synthetically investigated. L presents high selectivity and sensitivity for Cu2+ sensing in ethanol/HEPES buffer (v/v, 1 : 1), which is accompanied by the fluorescence switching "off" and subsequently "on" with the addition of EDTA. The mechanism for the detection of Cu2+ is further analyzed using 1H NMR titration, mass spectra and theoretical calculations. Furthermore, since the probe L possesses good photophysical properties, excellent biocompatibility and low cytotoxicity, it is successfully applied to track Cu2+ in the cellular endoplasmic reticulum by two-photon fluorescence imaging, showing its potential value for practical applications in biological systems.

Novel dual-functional fluorescent sensors based on bis(5,6-dimethylbenzimidazole) derivatives for distinguishing of Ag+ and Fe3+ in semi-aqueous medium

Three novel bisbenzimidazole derivatives have been synthesized and developed as dual-functional fluorescent sensors for the rapid and highly selective detection of Ag⁺ and Fe³⁺ ions in semi-aqueous medium with distinct spectral response for the first time. The absorption intensity is drastically decreased after the addition of Ag⁺. Contrarily, it is markedly increased upon the addition of Fe³⁺. And there is a good linear relation at low concentration of both Ag⁺ and Fe³⁺, which provides a quantitative method for their detection. Similarly, the sensors show a distinct fluorescence response towards Ag⁺ and Fe³⁺ with a different fluorescence color change under UV light. In addition, no significant changes and interference can be observed with other metal ions. The sensing mechanism studies confirm that the N atom in CN of benzimidazole ring of sensor 4a may bind with Ag⁺ or Fe³⁺ ion to form metal complex. And there is only a static quenching process for the 4-Ag⁺ complex system, but both dynamic and static quenching processes occur in the 4-Fe³⁺ complex system. Moreover, sensors 4 can steadily work in solution with a wide range of pH 4-13 and rapidly respond to Ag⁺ and Fe³⁺ with a response time of 10 s. Finally, the sensors have been successfully applied to the visual detection of Ag⁺ and Fe³⁺ not only in solution, but also in test paper.

Logic gate behavior and intracellular application of a fluorescent molecular switch for the detection of Fe3+ and cascade sensing of F− in pure aqueous media

The nature and coordination sites of a Schiff base 3,3′-(1E,1′E)-(1,3-phenylenebis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)dinaphthalen-2-ol (APHN), are tuned by its selective reduction to design a highly efficient fluorescent probe RAPHN.