A ratiometric fluorescent chemosensor for Al3+ in aqueous solution based on aggregation-induced emission and its application in live-cell imaging

A highly efficient, selective, reversible and ultra-sensitive fluorescence "Turn-ON" chemosensor for aluminium ions by a novel Schiff base

The synthesis of a Schiff base-based chemosensor, denoted as H6L, was accomplished through the condensation reaction of Isophthalohydrazide and 2,6-dihydroxybenzaldehyde in an ethanol solvent. The resulting compound was further characterized using 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, as well as high-resolution mass spectrometry (HRMS). Extensive research has been conducted on several facets of metal sensing phenomena, revealing that the Schiff base H6L demonstrates discerning and expeditious fluorescence sensing characteristics specifically towards Al (III) in acetonitrile. The purported method detects Al (III) can be ascribed to the suppression of photo-induced electron transfer (PET) and the enhanced chelation-induced fluorescence (CHEF). The stoichiometry of metal-ligand complexes (2:1) was determined using Job's plots titrations, HRMS and subsequently confirmed using NMR titration studies. The H6L sensors demonstrated remarkable fluorescence sensing capabilities in acetonitrile, with a low detection limit (LOD) of 0.44 μM. This LOD is suitably low for the detection of Al3+, which is commonly found in many environmental and biological systems. Fluorescence lifetime measurement provides additional evidence of complexation of H6L with Al (III). The reversibility of the sensor was demonstrated through the introduction of pyrophosphate (PPi), which forms a complex with aluminium ions, thereby releasing the chemo sensor for subsequent utilization. The findings suggest that H6L has the potential to serve as a viable probe for the detection and identification of Al3+ ions.

Extensive optical and DFT studies on novel AIE active fluorescent sensor for Colorimetric and fluorometric detection of nitrobenzene in Solid, solution and vapor phase

An electron rich isophthalamide based sensor IPA has been synthesized through a simple two-step reaction, containing noteworthy aggregation induced emission (AIE) properties. Considering the significant emission with λmax at 438 nm, sensor IPA has been employed for the sensing of nitrobenzene (NB) in solid, solution and vapor state with high sensitivity and selectivity. Sensor IPA showed noteworthy colorimetric and fluorometric quenching in fluorescence emission when exposed to NB. Small size of NB and involvement of photoinduced electron transfer (PET) lead to detection of NB down to 60 nM. IPA-NB interaction was studied through UV-Vis. spectroscopic studies along with fluorescence spectroscopy. Moreover, 1H and 13C NMR titration experiments provided additional support for determination of interaction type. Furthermore, by using density functional theory (DFT) calculations, thermodynamic stability was studied. Additionally, non-covalent interactions (NCI), frontier molecular orbitals (FMO), density of states (DOS), were investigated for providing further evidence of nitrobenzene sensing and its interaction with sensor. Natural bond orbital (NBO) analysis was carried out for charge transfer studies. Quantum theory of atom in molecule (QTAIM) and SAPT0 studies provided information about interaction points and binding energy. Additionally, IPA was investigated for NB sensing in real water samples, and its effective participation in solid state on-site detection as well as in solution phase was brought to light along with logic gate construction.

A zwitterionic probe for ratiometric fluorescent detection of aluminium(III) ion in aqueous medium and its application in bioimaging

In the present study, we have synthesized an aminobenzoic acid containing Schiff base (compound 1) and its structure was confirmed through single crystal X-ray study. Importantly, the compound 1 crystallizes in the zwitterionic form, with an anionic carboxylate group (-COO-) and a cationic iminium group (-C = NH+-). The compound 1 is highly soluble in water due to its zwitterionic feature in the solid state. Interestingly, compound 1 acts as a ratiometric fluorescent probe for the selective detection of Al3+ ion in aqueous solution without organic cosolvent. It can also detect Al3+ ion by visual colour change to bluish-green fluorescence under 365 nm UV light. The association constant between compound 1 with Al3+ ion was estimated to be 1.67 × 104 M-1. The lowest detection limit for Al3+ ion was calculated to be 7.05 × 10-8 M in water. Compound 1 in combination with Al3+ ion demonstrated fluorescent imaging potential of the nucleus of in RAW 264.7 murine macrophage cell line. In addition, the sensing model is developed as paper based sensor ''Test Kit' 'for its practical applicability.

A ratiometric solid AIE sensor for detection of acetone vapor

Acetone serves as a routine solvent and synthetic intermediate in chemical factories and laboratories. Monitoring the level of acetone vapor in working environment is of great necessity to employee health due to its strong volatility and toxicity, but there is still in lack of simple and easy-to-use portable sensors. In this study, we report a portable and intuitive indicator for real-time displaying acetone vapor concentration in air, based on the ratiometric fluorescence response of the designed organic molecule, PhB-SSB, to acetone. As an aggregation-induced emission (AIE) fluorophore, PhB-SSB underwent specific reaction with acetone through the salicylaldehyde Schiff base and phenylboronate groups to realize ratiometric fluorescence change from green to red after acetone vapor treatment. The reaction mechanism was proposed as acetone-induced breakage of the imine bond in PhB-SSB. We further fabricated PhB-SSB into a film fluorescent sensor for acetone vapor with good sensitivity and selectivity. Taking advantage of its intuitive fluorescent color contrast, acetone-specific response and small size, our sensor is practical in real-time alarming the acetone vapor hazard in the workplaces.

Highly sensitive naphthalimide based Schiff base for the fluorimetric detection of Fe3

A simple 1,8-naphthalimide based Schiff base probe (E)-6-((4-(diethylamino)-2-hydroxybenzylidene)amino)-2-(2-morpholinoethyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (NDSM) has been designed and synthesized for the specific detection of Fe3+ based on a fluorimetric mode. The absorbance of NDSM at 360 nm increased significantly in acetonitrile : water (7 : 3, v/v) medium only in the presence of Fe3+ ions with a visible colour change from yellow to golden yellow. Likewise, fluorescence emission intensity at 531 nm was almost wholly quenched in the presence of Fe3+. However, other competitive ions influenced insignificantly or did not affect the optical properties of NDSM. Lysosome targetability was expected from NDSM due to the installation of a basic morpholine unit. The LOD was found to be 0.8 μM with a response time of seconds. The fluorescence reversibility of NDSM + Fe3+ was established with complexing agent EDTA. Fe3+ influences the optical properties of NDSM by complexing with it, which blocks C[double bond, length as m-dash]N isomerization in addition to the ICT mechanism. The real-time application of Fe3+ was demonstrated in test paper-based detection, by the construction of a molecular logic gate, quantification of Fe3+ in water samples and fluorescence imaging of Fe3+.

An aggregation-induced emission active vitamin B6 cofactor derivative: application in pH sensing and detection of latent fingerprints

Aggregation-induced emission (AIE) properties of an easy-to-prepare and structurally planar Schiff base derivative of the vitamin B₆ cofactor pyridoxal (L) were investigated in DMSO–H₂O mixed solvents.

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.

Pyrene-phenylglycinol linked reversible ratiometric fluorescent chemosensor for the detection of aluminium in nanomolar range and its bio-imaging

Pyrene-phenylglycinol tangled ratiometric sensor (R)-1 was developed for the detection of Al³⁺ ion over other metal ions. Ratiometric behaviour of (R)-1 for Al³⁺ ion explained through monomer emission and excimer quenching leads to avoiding the π-π interactions of bis-pyrene rings. Pull-push to push-pull binding mechanism is successfully explained by DFT and sensing of Al³⁺-ions demonstrated in living cells. The LOD of (R)-1 for Al³⁺ downs to nanomolar concentrations which is lower than the allowed concentration of drinking water set by the (World Health Organization) WHO.

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.

Novel rhodamine-based colorimetric and fluorescent sensor for the dual-channel detection of Cu2+ and Co2+/trivalent metal ions and its AIRE activities

A rhodamine hydrazone 1 bearing coumarin moiety was designed and prepared. Compound 1 exhibited high selectivity toward Co²⁺ and trivalent metal ions with fluorescence enhancement in CH₃OH solution. However, 1 selectively responded to Al³⁺ in nearly pure H₂O media and was further applied to monitor Al³⁺ in live cells. Moreover, 1 could also act as a colorimetric probe toward Cu²⁺ in either CH₃OH or H₂O solution. In addition, sensor 1 displayed aggregation-induced ratiometric emission (AIRE) activities in mixed H₂O/CH₃OH solution.

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.

Water-soluble aluminium fluorescent sensor based on aggregation-induced emission enhancement

Development of a portable miniature system for Al(iii) detection in pure aqueous solutions using a novel AIEE compound.

A naphthalene-quinoline based chemosensor for fluorescent "turn-on" and absorbance-ratiometric detection of Al3+ and its application in cells imaging

A new naphthalene-quinoline based chemosensor L was prepared and structurally characterized. L exhibited excellent selectivity and sensitivity to Al³⁺ through distinct fluorescence enhancement (335-fold) and ratiometric detection in DMF/H₂O (v/v, 1/9) based on the combined mechanisms of ESIPT and CHEF. The recognizing behavior of L toward Al³⁺ had been investigated in detail through Job's Plot, FT-IR, HNMR, and HRMS analysis. The limit of detection (LOD) for Al³⁺ was as low as and 3.67 × 10^-8 M. L was successfully applied in real sample detection and construction of molecular logic gate. Moreover, L was verified to be of low cytotoxicity and good imaging characteristics for the detection of Al³⁺ in cells HSC.

A simple Schiff base as dual-responsive fluorescent sensor for bioimaging recognition of Zn2+ and Al3+ in living cells

A simple Schiff base fluorescent sensor (BDNOL) was synthesized from the reaction of picolinohydrazide and 4-(diethylamino)salicylaldehyde, and developed for selective detection of Al³⁺ and Zn²⁺. This non-fluorescent sensor displayed obvious fluorescence enhancement after binding to Al³⁺/Zn²⁺ ions with high sensitivity and selectivity, accompanied by obvious fluorescence emission enhancement (504 nm for Al³⁺ and 575 nm for Zn²⁺). The detection limits were found to be 8.30 × 10^-8 M for Al³⁺ and 1.24 × 10^-7 M for Zn²⁺. The binding mechanisms between BDNOL and Al³⁺/Zn²⁺ ions were supported by ¹H NMR and HR-MS analysis, and a density functional theory (DFT) study. The sensing behavior was also studied with molecular logic functions of OR, AND, and NOT gates. Furthermore, the fluorescent sensor was successfully used to recognize Al³⁺ and Zn²⁺ in living cells, suggesting that this simple biosensor has great potential in biological imaging applications.

A highly selective and sensitive fluorescent chemosensor and its application for rapid on-site detection of Al3

In this paper, a simple naphthalene-based derivative (HL) has been designed and synthesized as a Al³⁺-selective fluorescent chemosensor based on the PET mechanism. HL exhibited high selectivity and sensitivity towards Al³⁺ over other commonly coexisting metal ions in ethanol with a detection limit of 2.72nM. The 1:1 binding stoichiometry of the complex (HL-Al³⁺) was determined from the Job's plot based on fluorescence titrations and the ESI-MS spectrum data. Moreover, the binding site of HL with Al³⁺ was assured by the ¹H NMR titration experiment. The binding constant (Ka) of the complex (HL-Al³⁺) was calculated to be 5.06×10⁴M^-1 according to the Benesi-Hildebrand equation. In addition, the recognizing process of HL towards Al³⁺ was chemically reversible by adding Na₂EDTA. Importantly, HL could directly and rapidly detect aluminum ion through the filter paper without resorting to additional instrumental analysis.

A hydrazone based probe for selective sensing of Al(iii) and Al(iii)-probe complex mediated secondary sensing of PPi: framing of molecular logic circuit and memory device and computational studies

A hydrazone-based conjugate acts as a dual channel sensor towards Al³⁺and PPi in H₂O–MeOH with excellent sensing capability in live cells.

Sensitive ratiometric detection of Al(iii) ions in a 100% aqueous buffered solution using a fluorescent probe based on a peptide receptor

The peptidyl bioprobe detected Al(iii) ions sensitively in a 100% aqueous buffered solution through ratiometric response.

A coumarin based Schiff base probe for selective fluorescence detection of Al3+ and its application in live cell imaging

A new coumarin based Schiff base compound, CSB-1 has been synthesized to detect metal ion based on the chelation enhanced fluorescence (CHEF). The cation binding properties of CSB-1 was thoroughly examined in UV-vis and fluorescence spectroscopy. In fluorescence spectroscopy the compound showed high selectivity toward Al³⁺ ion and the Al³⁺ can be quantified in mixed aqueous buffer solution (MeOH: 0.01M HEPES Buffer; 9:1; v/v) at pH7.4 as well as in BSA media. The fluorescence intensity of CSB-1 was enhanced by ~24 fold after addition of only five equivalents of Al³⁺. The fluorescence titration of CSB-1 with Al³⁺ in mixed aqueous buffer afforded a binding constant, K_a=(1.06±0.2)×10⁴M^-1. The colour change from light yellow to colourless and the appearance of blue fluorescence, which can be observed by the naked eye, provides a real-time method for Al³⁺ sensing. Further the live cell imaging study indicated that the detection of intracellular Al³⁺ ions are also readily possible in living cell.

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 simple Schiff base (BMSA) prepared from salicylaldehyde and 2-(1H-benzo[d]imidazol-2-yl)aniline was evaluated as an efficient fluorescent chemosensor for the selective recognition of Al³⁺and Cu²⁺ over other common metal ions. This sensor could detect Al3⁺ in CH₃OH/PBS with distinct emission red-shift (the detection limit 0.31μM)and Cu²⁺in CH₃OH/Tris-HCL (the detection limit 0.54μM) with obvious fluorescence quenching. The obtained BMSA-Al³⁺ and BMSA-Cu²⁺ complexes could act as cascade sensors for detecting F^- and S^2-, respectively. The recognizing behavior of BMSA toward Al³⁺and Cu²⁺ has been investigated in detail through Job's Plot, FT-IR NMR, and HRMS analysis. Moreover, this chemosensor was verified to be of low cytotoxicity and good imaging characteristics for the detection of Al³⁺ and Cu²⁺, and further for the recognition of F^- and S^2- in living cells, suggesting that BMSA was proved to be a useful tool for tracking Al3⁺/Cu²⁺and F^-/S^2- ions in vivo.

A highly selective and sensitive fluorescent turn-on Al3+ chemosensor in aqueous media and living cells: experimental and theoretical studies

A highly selective and sensitive fluorescent chemosensor exhibited enhanced fluorescence in the presence of Al³⁺ and in living cells.

A simple-structured acridine derivative as a fluorescent enhancement chemosensor for the detection of Pd2+ in aqueous media

4,5-Bis(hydroxymethyl) acridine (sensor 1) has been discovered and synthesized as a simple-structured Pd(2+) fluorescent probe. Sensor 1 showed highly selective recognition toward Pd(2+) over other examined metal ions in aqueous solution. Under the optimized condition, fluorescence intensity was linearly proportional to the concentration of Pd(2+) in the 0-1 μM concentration range with detection limits of 0.021 μM. The EDTA-adding and stoichiometry experiments indicated that sensor 1 was a reversible chemosensor for Pd(2+) with a 2:1 ligand/metal complex at neutral pH. Moreover, the sensor 1 was also successfully applied to determination of Pd(2+) in water samples and palladium-containing catalyst, which made it attractive for sensing applications.