Chelation-enhanced Fluorescence Effect Research Articles

An eugenol-sulfonyl based fluorescent probe for recognition of Al3+ in real sample analysis and biological application

The present work describes an eugenol-sulfonyl based fluorescence chemosensor, H4L [H4L=6,6′-((1E,1′E)-((sulfonylbis(6-hydroxy-3,1- phenylene))bis(azanylylidene))bis(methanylylidene))bis(4-allyl-2-methoxyphenol)], which shows maximum emission intensity towards Al3+ ion in presence of other competing metal ions. Upon excitation at 440 nm H4L exhibits a significant rise in fluorescence at 547 nm upon gradual addition of Al3+ ion in the HEPES buffer at pH=7.4 (MeOH:H2O, 4:1, (v/v)). The increasing value of fluorescence is mainly due to chelation enhanced fluorescence effect (CHEF). Complete characterization of the probe (H4L) and metal bound complex (1) have been determined using a range of methods including UV–Vis absorption titration, fluorescence titration, NMR, ESI-mass, etc. Thus 1:2 binding stoichiometry between H4L and metal ion has been also proved. Another important aspect: regeneration and reversibility of H4L are investigated in presence of Na2EDTA. H4L exhibits ∼ 10−6 M order detection limit and significant binding constant (∼106 M−1) for the Al3+ ion, suggesting its potential use in bio-imaging studies. The probe was effectively used in real samples as well as paper strip to locate the Al3+ ion.

Silver induced self-assembly of a rhodanine derived reversible fluorescent chemosensor: Applications in smart-phone color assist app, logic gate, real sample analysis and bio-imaging

An innovative chemosensor, Rhodanine-appended benzaldehyde (RB), was developed and analyzed using spectroscopic methods to detect silver ions (Ag+) in a THF–H2O buffer solution via fluorimetry. The RB probe exhibited low fluorescence due to C-N free rotation and inhibition of electron transfer. However, interaction with Ag+ ions resulted in a noteworthy redshift of approximately 6 nm and increased fluorescence intensity owing to the chelation-enhanced fluorescence (CHEF) effect, which hindered the Intramolecular Charge Transfer (ICT) process. The binding ratio between RB and Ag+ ions was determined to be 2:1 using the job plot method. The association constant (Ka) was calculated to be 4.84 × 105 M−1 and further confirmed through ESI-TOF spectroscopic and DFT analyses. The limit of detection (LOD) and quantification (LOQ) for RB in binding with Ag+ ions were found to be 1.7 × 10−8 M and 5.4 × 10−8 M, respectively. Additionally, the color changes of RB when binding with Ag+ ions were effectively leveraged in an RGB-assisted smartphone color analysis app for precise sample analysis for Ag+ ion detection. Most importantly, the RB probe’s ability to detect silver ions in the E. coli pathogen was successfully demonstrated, providing reassurance about its practical application, using a confocal scanning electron microscope via the green channel.

An AIE dynamic a highly selective and expeditious benzothiazole-pyrazine based colorimetric chemosensor for Ni2+and fluorogenic chemosensor for Cu2+ and Al3+ detection

Considerable research focus has been devoted to the advancement of single-component sensors that can identify several analytes. In this regard, a complex chemosensor called BPA was created by building an imine link between benzothiazole and pyrazine. On the flexible imine link, the nitrogen atoms with lone pair electrons were arranged as possible coordination sites to enable changes in molecular configurations and charge transfer. In the aqueous acetonitrile environment, BPA displayed the discriminative identification of Ni2+ by a chromogenic response (color transition from colorless to yellow) and a fluorescence “decreasing” response for Cu2+ via ligand–metal charge transfer. Additionally, BPA exhibited recognition of Al3+ through a “turn-on” fluorogenic response facilitated by the chelation-enhanced fluorescence effect. The detection limits for Ni2+, Al3+, and Cu2+ were remarkably low, measuring 5.19 nM, 16 nM, and 214 nM, respectively. A 1:1 binding stoichiometry and precise complex modes between BPA and the target metal ions were successfully determined using extensive investigations, which encompassed the utilization of Job's plot, mass spectra, NMR, and DFT analysis. The deduced coordination mechanisms were corroborated by computational and experimental methodologies. BPA's potential practical uses were demonstrated by subsequently evaluating its ability to identify Ni2+, Al3+, and Cu2+ in actual water samples and validating its performance on-site using test strips.

Ferrocene-based chemosensor creates molecular logic circuit for selective detection of Hg2+ and Cu2+

A cation sensor, R, with multi-channel signaling was developed by creating a covalent connection between a ferrocene unit and pyridyl-pyrazole rings. Spectroscopic techniques and single-crystal X-ray diffraction were employed to characterize sensor R. The examination revealed a dihedral angle of 140.09° for the pyridyl-pyrazole rings. The receptor R functions as a highly selective multi-channel chemosensor, exhibiting chromogenic, fluorogenic, and electrochemical capabilities. In a CH3CN/water (9:1) solvent mixture, receptor R operates as a multi-channel signaling chemosensor, selectively detecting Hg2+ and Cu2+ ions in water. The original pale-yellow solution turned orange upon Hg2+ addition and green upon Cu2+ addition. A new low energy (LE) band at 460 nm was detected after adding one equivalent of Hg2+. In cyclic voltammetry (CV), the half-wave potential (E1/2) of 462 mV shifted to 622 mV, whereas in differential pulse voltammogram (DPV), the oxidation peak underwent an anodic shift (ΔE1/2 = 155 mV). The maximum emission at 423 nm was lowered by more than 90 % when the concentration of Hg2+ ions reached one equivalent. One equivalent addition of Cu2+ results in a new LE band at 740 nm. Cu2+ ions suppress the oxidation peak current in both the CV and DPV of R. It also demonstrates chelation-enhanced fluorescence effect (CHEF) with Cu2+. The interaction between cations and R was elucidated through 13C NMR titration. DFT calculations revealed the binding mode. Its distinctive fluorescence demonstrates a 'turn-on' response to Cu2+ and a 'turn-off' response to Hg2+ with selectivity. This concept has been applied to create a molecular combinatorial logic circuit.

Heterocyclic fluorescent Schiff base chemosensors for the detection of Fe(III) and Cu(II) ions.

Two new Schiff bases were synthesized from 1-(2,4-dihydroxyphenyl)ethanone and pyridine derivatives. Both compounds were characterized using infrared, UV-Vis., 1H NMR, 13C NMR and mass spectral studies. Density functional theory (DFT) calculations were performed for both the Schiff bases with 6-31G(d, p) as the basis set. Vibrational frequencies calculated using the theoretical method were in good agreement with the experimental values. Both the Schiff bases were highly fluorescent in nature. The cation-recognizing profile of the compounds was investigated in aqueous methanol medium. The Schiff base 4-(1-(pyridin-4-ylimino)ethyl)benzene-1,3-diol (PYEB) was found to interact with Fe(III) and Cu(II) ions, whereas the Schiff base 4,4'-((pyridine-2,3-diylbis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(benzene-1,3-diol) (PDEB) was found to detect Cu(II) ions. The mechanism of recognition was established as combined excited state intramolecular proton transfer (ESIPT)-chelation-enhanced fluorescence (CHEF) effect and chelation-enhanced quenching (CHEQ) process for the detection of Fe(III) and Cu(II) ions, respectively. The stability constant of the metal complexes formed during the sensing process was determined. The limit of detection for Fe(III) and Cu(II) ions with respect to Schiff base PYEB was found to be 1.64 ×10-6 and 2.16 ×10-7M, respectively. With respect to Schiff base PDEB, the limit of detection for Cu(II) ion was found to be 4.54 ×10-4M. The Cu(II) ion sensing property of the Schiff base PDEB was applied in bioimaging studies for the detection of HeLa cells.

Dual-channel fluorescent probe utilizing hydrazone for Zn2+ and Hg2+ detection: Exploring distinct signaling mechanisms and applications in bioimaging and latent fingerprint analysis

A facile Schiff base probe C1 has been developed and evaluated using 1H, 13C NMR, and mass spectroscopy. Fluorescence investigations were conducted to determine probe-sensing behavior. Probe C1 demonstrated sensitive, and selective recognition of Zn2+ and Hg2+ ions by using two distinct processes (i.e., chelation enhanced fluorescence effect and fluorescence quenching) over other cations in ACN-H2O (8:2, v/v). The Zn2+ and Hg2+ detection limits of 0.042 and 0.081 μM are achieved with the probe C1. C1 has a binding constant of 3.33 × 103 M−1 for Zn2+ and an emission quenching constant of 1.22 × 104 M−1 for Hg2+. A Jobs plot was used to determine the binding stoichiometry of C1 and Zn2+/Hg2+ ions ratio is 1:1. By using Zn2+/Hg2+ and EDTA additions alternately, the probe's reusability was investigated. Moreover, the probe was found to be highly cytocompatibility using an MTT assay in a mouse fibroblast cell line (NIH3T3). Further, the probe was found to visualize Zn2+ and Hg2+ ions inside the cells, indicating the potential application of the probe as an intracellular probe to detect Zn2+ and Hg2+ ions. The probe shows very good solid-state emission behavior, this motivates us to develop latent fingerprint detection and anticounterfeiting applications.

Al3+ induced hydrolysis of anthraquinone-based Schiff base fluorescent probe for determination PPi ions and bioimaging

Herein, a novel anthraquinone derivative appended fluorescent probe (HAD), has been developed as a reversible probe for detection of aluminium ions (Al3+) and pyrophosphate (PPi) in buffer medium. The probe displays fluorescence “turn-on” response towards Al3+ with high specificity. The activation of the chelation-enhanced fluorescence (CHEF) effect occurs as a consequence of the formation of a complex via coordination with Al3+, which was due to the imine bond is dynamic and reversible and further causing subsequent cleavage of the -C=N bond in the presence of Al3+. This complex significantly amplifies the fluorescence response. Additionally, according to the Job's plot and high-resolution mass spectrometry (HRMS) measurements, the binding stoichiometry of HAD and Al3+ ions is 1:2. Moreover, Density functional theory (DFT) investigations further elucidate the binding mechanism. The original spectrum is restored after the addition of PPi, which is due to the formation of more stable Al3+-PPi complex. The specific determination of Al3+ and PPi with the detecting limit of 47.6 nM and 73.7 nM (S/N = 3), respectively. Due to its exceptional biocompatibility, the probe has facilitated the development of Al3+ and PPi imaging in vitro and in vivo, thereby showcasing its remarkable capabilities in the realm of environmental and biological analysis.

Anthraquinone-metal complex fluorescence sensing platform for monitoring PPi mediated by Al3+ and bioimaging

Anions are widely found in humans and the environment. The analysis of its content and distribution shows great potential in the fields of life science, environmental science and biochemical reactions. Herein, a new anthraquinone derivative appended fluorescent probe (HBD) was developed as a reversible fluorescent probe for the detection pyrophosphate (PPi) in methanol/urotropine buffer medium (1:1, v/v, pH 4.5). The probe displayed fluorescence “turn-on” response towards Al3+ with high specificity. Due to the cleaving of the -CN bond and subsequent creation of complex caused by coordination with Al3+, the chelation-enhanced fluorescence (CHEF) effect was activated, resulting in a significantly enhancement fluorescence response. Further, 1H NMR titration and HRMS analysis revealed that the Al3+ induced hydrolysis occurs on one side of the Schiff base and led to the formation of free primary amine compound. Moreover, the binding mechanism was also recognized density functional theory (DFT) studies. Due to the strong binding ability of PPi and Al3+, PPi could remove Al3+ from the complex, causing fluorescence quenching. The specific determination of Al3+ and PPi with the detecting limit of 31.6 nM and 56.8 nM. Due to its good biocompatibility, the sensor was successfully applied to fluorescence imaging of Al3+ and PPi in HeLa cells and zebrafish. The results show that HBD has broad application prospects in environmental and biological analysis.

An excimer process induced a turn-on fluorescent probe for detection of ultra-low concentration of mercury ions.

The accumulation of mercury pollution in plants can induce severe injury to human beings. It is a great challenge to monitor ultra-low concentrations of mercury in complicated matrixes. In this study, we successfully developed a strategy via Hg2+-triggered naphthalene-based fluorescent probe 1, which formed excimer that subsequently emitted fluorescence for the successful detection of ultra-low concentrations of Hg2+. The coordination of N and S atoms with Hg2+ facilitated the formation of excimer from the naphthalene-conjugated planes that were in sufficiently close proximity. Suppression of CN bond rotation also induced the chelation-enhanced fluorescence (CHEF) effect, and the cumulative result of these effects was obvious fluorescent enhancement. Compared with probe 2, the other key factor for detection of Hg2+ is that the electrons of the hydroxyl group can easily transfer to a naphthalene moiety, resulting in an augmented π-electron density that enhanced the π-π stacking of the naphthalene-conjugated excimer. After detailed spectral studies and mechanism discussions, it was realized that probe 1 was able to detect ultra-low concentrations of Hg2+ in PBS buffer solution. The detection limit was calculated to be 1.98 nM. On account of the excellent performances, the probe was successfully applied in monitoring Hg2+ in water and pea sprouts with the potential for application as an advanced warning of contamination.

Turn-on detection of Al3+ ions using quinoline-based tripodal probe: mechanistic investigation and live cell imaging applications.

In this study, an easily synthesizable Schiff base probe TQSB having a quinoline fluorophore is demonstrated as a fluorescent and colorimetric turn-on sensor for Al3+ ions in a semi-aqueous medium (CH3CN/water; 4 : 1; v/v). Absorption, emission and colorimetric studies clearly indicated that TQSB exhibited a high selectivity toward Al3+, as observed from its excellent binding constant (Kb = 3.8 × 106 M-1) and detection limit (7.0 nM) values. TQSB alone was almost non-fluorescent in nature; however, addition of Al3+ induced intense fluorescence at 414 nm most probably due to combined CHEF (chelation-enhanced fluorescence) and restricted PET effects. The sensing mechanism was established via Job's plot, NMR spectroscopy, ESI-mass spectrometry, and density functional theory (DFT) analyses. Furthermore, to evaluate the applied potential of probe TQSB, its sensing ability was studied in real samples such as soil samples and Al3+-containing Digene gastric tablets as well as on low-cost filter paper strips. Fluorescence microscopy imaging experiments further revealed that TQSB can be used as an effective probe to detect intracellular Al3+ in live cells with no cytotoxicity.

A fluorescence turn “on-off” imaging probe for sequential detection of Al3+ and L-Cysteine in HeLa cells

At this “Aluminum Age”, exposure to aluminum (metallic or ionic form) is inevitable and inestimable. The presence of aluminum in biological systems is evident but more often aluminum toxicity is less understood. Therefore, the presence of biologically reactive aluminum needs to be identified and quantified. Alongside metals, L-cysteine, an essential amino acid, plays a pivotal role in the homeostasis of cellular oxidative and reductive stress. However, excess (<7g) could be lethal and can lead to death. Thus, in-situ selective detection of aluminum and L-cysteine is of larger interest. Here we report a fluorogenic probe (R) for the sequential selective detection and quantification of Al3+ and L-cysteine in a semi-aqueous medium (3:7; water: DMSO). The probe (R) was synthesized by a one-step acid-mediated condensation reaction between pyridine-3,4-diamine and 2-hydroxy-1-napthaldehyde. The synthesized probe was characterized using 1H and 13C NMR, and HR-Mass spectroscopic techniques. The probe (R) is non-emissive in nature, but on recognition of Al3+, the probe R showed “turn-on” emission (bright yellow colour) showing two emission maxima (522 nm and 547 nm), and no naked eye observable color change. Other competing cations do not show any noticeable fluorescence outcome. The R + Al3+ ensemble can specifically detect L-cysteine among all the essential amino acids by showing a fluorescence “turn-off” response. The sensing mechanism of Al3+ is obeying the chelation-enhanced fluorescence (CHEF) effect. The binding constant of R + Al3+ is 0.3 × 104 M−1. The limit of detection (LoD) for Al3+ and L-cysteine are 2.02 × 10-7 M and 0.5 × 10-5 M respectively. The probe (R) can show maximum efficiency within the pH range (7.0–10.0). The probe is found non-toxic (>80 % cell viability with 15 µM concentration) and employed for the in-vitro fluorescence imaging in the HeLa cell.

An aggregation-induced emission-based ratiometric fluorescent chemosensor for Hg(II) and its application in Caenorhabditis elegans imaging

A chromone-based ratiometric fluorescent probe L2 was developed for the selective detection of Hg(II) in a semi-aqueous solution based on aggregation-induced emission (AIE) and chelation-enhanced fluorescence (CHEF) effect. The probe L2 fluoresced significantly at 498 nm in its aggregated state, and when chelated with Hg(II), the soluble state fluoresced 1-fold higher. In addition, Job’s plot reveals that the probe forms a 1:1 stoichiometry complex with Hg(II) with an association constant of 9.10 × 103M−1 estimated by the BH plot. The probe L2 detects Hg(II) down to 22.47 nM without interference from other interfering ions. The FTIR, ESI mass, and DFT-based computational studies investigated the binding mechanism of probe L2 with Hg(II). Taking advantage of its AIE characteristics, the probe L2 was successfully applied for bio-capability analysis in Caenorhabditis elegans (a nematode worm) imaging of Hg(II) in a living model.

Anthraquinone-based Schiff base fluorescent probe for the sequential sensing of Al3+ and pyrophosphate in a near-perfect aqueous solution and bioimaging

A new anthraquinone derivative fluorescent probe (DPHA) was designed and synthesized for sequentially detecting aluminum ions and pyrophosphate (PPi) in a near-perfect aqueous medium with 0.4 % DMSO as a co-solvent. The DPHA probe displayed “turn-on” fluorescence sensing of Al3+ at 575 nm, overcoming the interference of the other common cations through an apparent color variation from purple to light pink. Anthraquinone-derived conjugated skeleton and Schiff base-mediated multiple binding sites were responsible for the sensitive fluorescence response and selective recognition, respectively, thus producing a chelation-enhanced fluorescence effect. Furthermore, Job's plot analysis and high-resolution mass spectrometry (HRMS) studies supported the formation of a 1:1 ligand/metal complex for Al3+. The plausible binding mechanism was recognized by both experimentally and theoretically. The succeeding addition of PPi regenerated the original spectrum of DPHA and thus the strong affinity of Al3+ to PPi. The in-situ formed DPHA-Al3+ complex for selective identification of PPi by electrostatic interaction by drawing out Al3+ and releasing the DPHA probe. Except for specific recognition of Al3+ and PPi with corresponding low detection limits of 42.2 nM and 65.2 nM (S/N = 3). Owing to its good biocompatibility, DPHA also applied as a visual probe for monitoring Al3+ ions and PPi in living cells and zebrafish, demonstrating its outstanding potential in biological work.

Multi-spectroscopic, TD-DFT and bio-imaging studies of new Schiff base optical probe for the detection of CN− and Al(III) ions

The selective and sensitive dual channel assay of CN− and fluorescence assay of Al(III) are reported using a simple organic probe (VDP1) in aqueous and non-aqueous media. The binding behaviours of these ionic analytes with VDP1 were studied using UV–Vis, fluorescence, (1H, 13C & 27Al) NMR and mass spectral techniques. VDP1 showed a highly selective change of colour and fluorescence enhancement with CN− ion immediately without interference from other anions. The experimental results revealed that the mechanism of CN− detection involves deprotonation of the phenolic -OH group followed by nucleophilic addition at the imine C-atom. The addition of Al(III) was found to enhance the fluorescence of VDP1 significantly through chelation-enhanced fluorescence effect (CHEF) by forming a 1:1 octahedral complex [Al(VDP1)(NO3)3(H2O)]. The Density Functional Theory (DFT) and Time-dependent Density Functional Theory (TD-DFT) based theoretical calculations confirmed that the weak fluorescence of VDP1 is due to the charge transfer (CT) character of the transition in which non-radiative decay dominates. The theoretically computed optical properties matched well with that of experimental observations. The limits of detection (LOD) of these ionic analytes were also calculated and found to be much lower than the corresponding recommended limit set by the World Health Organization (WHO). MTT assay indicated that VDP1 is less toxic to HeLa cells and could detect intracellular CN− and Al(III) ions by bioimaging.

A dual-function fluorescence 'turn-on' probe that allows Zn (II) bioimaging and quantification of water in the organic solvent.

Herein, a Eugenol-derived fluorescence 'turn-on' probe FLHE was synthesized by condensing 2-((3-(trifluoromethyl)phenyl)amino)benzohydrazide with 5-allyl-2-hydroxy-3-methoxybenzaldehyde. FLHE demonstrated very low fluorescence in the studied organic solvents of varying polarities. However, upon titration with Zn2+ in HEPES buffer (pH=7.4, 50% ACN, v/v), FLHE showed 40-fold higher fluorescence signals indicating the formation of the FLHE-Zn2+ complex. The fluorescence turn-on phenomenon upon FLHE-Zn2+ complex formation results from a chelation-enhanced fluorescence (CHEF) effect. The FLHE-Zn2+ complexation demonstrated a stokes shift of 156nm (λex=350nm, λem=506nm) and an about 33-fold increase in the quantum yield (FLHE, Φ=0.007; FLHE-Zn2+ complex, Φ=0.23). The binding constant (Ka) determined by the Benesi-Hildebrand plot for interaction between FLHE and Zn2+ was 5.33×103 M-1. FLHE demonstrated a LOD of 31.8nM for detecting Zn2+ in the environmental samples without interference from other cations and anions. FLHE-based paper strip (FLHE-PS) assay was developed to quantify the Zn2+ ions in water and the water content of organic solvent. FLHE-PS allows the detection of Zn2+ in aqueous solutions with a LOD of 63.2nM and quantifying water in acetonitrile with a LOD of 0.14%. These results indicate that the FLHE has high applicability for detecting Zn2+ in living cells and environmental samples and detecting the presence of water in the organic solvents.

X-ray structure, chelation enhanced fluorescence effect, thermal and redox properties of a new europium(III) complex based on bioactive naphthoquinone

The synthesis of metal complexes containing natural naphthoquinones has been highlighted due to their interesting electrochemical and spectroscopic properties, which may have a primordial influence on their pharmacological bioactivities. Simultaneously, processes of interaction of lanthanoid ions with organic ligands indicate the formation of coordination compounds that have marked luminescent properties of technological and medical diagnostic interest. Thus, this work describes the synthesis, characterization, and study of the properties of a new lawsone-EuIII metal complex, including the structural determination by XRD and the thermal, redox, and luminescent properties. The nine-coordinated complex exhibits a tri-hooded trigonal prismatic geometry, in which the metal ion is bound to nine oxygen atoms from three lawsone molecules and three water molecules, and the molecular structure still has approximately four water molecules as solvates, thus constituting [EuIII(C10H5O3)3(H2O)3].4H2O (FW = 797.49 g mol−1). The average CO and CC bond lengths indicate that naphthoquinone is coordinated in its anionic form, while the structural conformation shows intermolecular hydrogen interactions, which form interesting water channels. Thermal analyzes provided information regarding the decomposition behavior of the compound and its thermodynamic stability involving endothermic and exothermic processes. Electrochemical studies of the complex show that the processes associated with the ligand are shifted, with concomitant reduction of the Eu3+ ion. This new rearrangement is also responsible for differences in electronic transitions, such as the effect of increasing luminescence intensity (CHEF effect), and the phenomenon occurs through the antenna-like intramolecular interaction of the lawsonate anion with the europium(III) ion.

Design and synthesis of a hydrazinopthalazine derived chemosensor to detect metal ions Zn2+, Al3+ via CHEF effect with biological study and theoretical calculation

A multiple metal ion detector, H3L [H3L = 4-methyl-2,6-bis((E)-(2-(phthalazin-1-yl)hydrazono)methyl)phenol] has been synthesized upon mixing 2,6-diformyl-4-methylphenol (DFP) and hydrochloride salt of hydrazinopthalazine in 1:2 ratio. H3L successfully detects Zn2+ and Al3+ ions through fluorescence enhancement in HEPES buffer (1:9, MeOH:H2O, v/v, pH 7.4). The fluorescent probe and its metal-bound compounds (1 and 2) are characterized using different spectroscopy and mass spectrometric techniques. The turn-on fluorescence response towards Zn2+ and Al3+ was explained based on PET-OFF, and chelation enhanced fluorescence (CHEF) ON processes. The binding mode and sensing mechanism of compounds 1 and 2 were confirmed using DFT calculations. H3L exhibits low detection limits and strong binding constants towards Zn2+ (2.37 × 10−6 M and 3.49 × 104 M−1) and Al3+ (1.32 × 10−6 M and 2.67 × 104 M−1) ions. It is successfully used in paper strips for the detection of Zn2+ and Al3+. Biocompatible H3L also applied as a visual probe for the practical determination of Zn2+ and Al3+ on cervical cancer cells.

Fluorescent Turn-On Anthracene-Based Aluminum(III) Sensor for a Therapeutic Study in Alzheimer's Disease Model of Drosophila.

A new anthracene-based probe (E)-N'-(1-(anthracen-9-yl)ethylidene)-2-hydroxybenzohydrazide (AHB) has been efficiently synthesized and characterized by various spectroscopic methods. It exhibits extremely selective and sensitive fluorometric sensing of Al3+ ions with a large enhancement in the fluorescent intensity due to the restricted photoinduced electron transfer (PET) mechanism with a chelation-enhanced fluorescence (CHEF) effect. The AHB-Al3+ complex shows a remarkably low limit of detection at 0.498 nM. The binding mechanism has been proposed based on Job's plot, 1H NMR titration, Fourier transform infrared (FT-IR), high-resolution mass spectrometry (HRMS), and density functional theory (DFT) studies. The chemosensor is reusable and reversible in the presence of ctDNA. The practical usability of the fluorosensor has been established by a test strip kit. Further, the therapeutic potential of AHB against Al3+ ion-induced tau protein toxicity has been tested in the eye of Alzheimer's disease (AD) model of Drosophila via metal chelation therapy. AHB shows great therapeutic potential with 53.3% rescue in the eye phenotype. The in vivo interaction study of AHB with Al3+ in the gut tissue of Drosophila confirms its sensing efficiency in the biological environment. A detailed comparison table included evaluates the effectiveness of AHB.

Two novel “turn on” fluorescent probes for the determination of Al3+ and its applications

In this paper, two “turn on” fluorescent probes Y1 and Y2 were obtained by a simple one-step reaction, which can detect Al3+ based on the cation-induced CHEF (chelation enhanced fluorescence) effect. Both probes show highly selectivity, and the other common fifteen cations have no influence on the detection. What is more important, Y1 and Y2 also exhibit high sensitivity to Al3+, especially for Y2, their limits of detection (LOD) are 15.5 nM and 0.166 nM, respectively, which are lower than many effectively reported probes. Sensors Y1 and Y2 have a pincer-shaped structure which can combine with Al3+ to form a six-membered ring, strengthening complexing power. Job plots and ESI-MS revealed that both probes coordinated to Al3+ with the ratio 1:1, 1H NMR and DFT calculations demonstrated the probes combined with Al3+ through the tetracoordination process with one nitrogen atom in NH and three oxygen atoms in two OH and one CO groups, respectively. Practical application including test strips, soil and Traditional Chinese Medicine (TCM) experiments manifest that these probes can be further used for Al3+ detection in various complex environments.

Spectral and DFT/TD-DFT studies on turn-on fluorescent detection of Al(III) by a quinolin-8-ol-based Schiff base and its bioimaging

A new Schiff base (AK2) is synthesized, characterized and used to detect Al(III) ions as the fluorometric probe in an aqueous solution. AK2 exhibits high selectivity towards Al(III) by forming a 1:1 octahedral complex wherein the probe acts as a NNN-tridentate ligand. The sensing mechanism is verified by 1H NMR, 27Al NMR and mass spectral techniques in addition to Job's plot analysis. In an aqueous solution, AK2 is scarcely emissive due to the photoinduced electron transfer (PET) process and upon the addition of Al(III) ions the formed AK2+Al(III) complex results in instantaneous intense bluish-green emission (at 475 nm) by chelation-enhanced fluorescence (CHEF) effect. AK2 was found to have high selectivity, high binding constant (Kb = 3.9 × 104 M−1) and an acceptable limit of detection (LOD = 0.9 µM). The experimentally observed optical properties of AK2 and AK2+Al(III) complex have been correlated with computational results using B3LYP/6–311G** and B3LYP/LACV3P** basis sets by Density Functional Theory (DFT) and Time-dependent Density Functional Theory (TD-DFT) methods. The probe has proved its real-time application as a reagent in the quantitative determination of Al(III) in natural matrices such as bore water, drinking water, tap water and BSA solution. Fluorescence microscopic studies showed that AK2 could be used as an effective probe for detecting intracellular Al(III) in HeLa cells without toxicity.