A highly selective turn-on fluorescent probe for Al(III) based on coumarin and its application in vivo

Uncovering the sensing mechanism of a zinc ion sensor: Fluorescence enhancement induced by the elimination of the TICT state

Precise detection of zinc ion is of fundamental importance in the fields of environment protection and food safety. A comprehensive understanding of the sensing mechanism will help to the design of such sensors. The detailed photophysical process of a zinc ion sensor as well as the sensing mechanism are uncovered with the aid of density functional theory (DFT) and time-dependent density functional theory (TDDFT). Both the ground state and first excited state potential energy surfaces (PES) of the sensor are carefully explored to reveal the photo-physical process of the sensor. Excited state intramolecular proton transfer (ESIPT) is observed on the S1 state PES. Then, the twist motion of C=N double bond is triggered after the ESIPT process, which leads to a twisted intramolecular charge transfer (TICT) state. This TICT state is found to make the sensor non-emissive. With the addition of Zn2+, the TICT state is eliminated which greatly enhances the fluorescence of the sensor and achieves zinc ion detection. The interaction of the sensor with Cd2+ and Hg2+ are also explored, which well explains the good selectivity of the sensor.

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.

Sensitive ratiometric sensor for Al(III) detection in water samples using luminescence or eye-vision

A facile, quick, and sensitive ratiometric luminescence sensor is designed for detection aluminum ions in water samples using luminescence or eye-vision. This approach relies on the emission change of the europium(III) complex with 3-(2-naphthoyl)-1,1,1,-trifluoro acetone (3-NTA) after interaction with various concentration of aluminum ions. The addition of aluminum ions suppressed the Eu(III) emission at 615 nm under 333 nm excitation, while simultaneously enhancing the ligand emission at 480 nm. Optimum detection was obtained in methanol. The quantification of aluminum ions using ratiometric method was determined by plotting the luminescence ratio (F_480nm/F_615nm) versus aluminum ions concentration. The calibration plot was obtained within the range 0.1-100 µM with LOD = 0.27 µM. Additionally, the concentration of aluminum ions can be estimated semi-quantitatively by visually observing the luminescence colour change of the probe from red to light green and then to dark green after being excited by a UV lamp with 365 nm. As far as we are aware, this is the first luminescent lanthanide complex-based ratiometric probe for the detection of aluminum ions. The probe showed remarkable aluminum ions selectivity relative to that of other metal ions. The suggested sensor was used effectively to identify aluminum ions in water samples with good results.

Hierarchical Ti-MOF Microflowers for Synchronous Removal and Fluorescent Detection of Aluminum Ions

Bifunctional luminescence metal-organic frameworks with unique nanostructures have drawn ongoing attention for simultaneous determination and elimination of metal ions in the aqueous environment, but still remain a great challenge. In this work, three-dimensional hierarchical titanium metal-organic framework (Ti-MOF) microflowers were developed by a secondary hydrothermal method for not only highly sensitive and selective detection of Al(III), but also simultaneously efficient decontamination. The resulting Ti-MOF microflowers with a diameter of 5-6 μm consisted of nanorods with a diameter of ∼200 nm and a length of 1-2 μm, which provide abundant, surface active sites for determination and elimination of Al(III) ions. Because of their substantial specific surface area and superior fluorescence characteristics, Ti-MOF microflowers are used as fluorescence probes for quantitative determination of Al(III) in the aqueous environment. Importantly, the specific FL enhancement by Al(III) via a chelation-enhanced fluorescence mechanism can be utilized for selective and quantitative determination of Al(III). The Al(III) detection has a linear range of 0.4-15 µM and a detection limit as low as 75 nM. By introducing ascorbic acid, interference of Fe(III) can be avoided to achieve selective detection of Al(III) under various co-existing cations. It is noteworthy that the Ti-MOF microflowers exhibit excellent adsorption capacity for Al(III) with a high adsorption capacity of 25.85 mg g^-1. The rapid adsorption rate is consistent with a pseudo-second order kinetic model. Ti-MOF is a promising contender as an adsorbent and a fluorescent chemical sensor for simultaneous determination and elimination of Al(III) due to its exceptional water stability, high porosity, and intense luminescence.

Water-soluble optical sensors: keys to detect aluminium in biological environment

Metal ion plays a critical role from enzyme catalysis to cellular health and functions. The concentration of metal ions in a living system is highly regulated. Among the biologically relevant metal ions, the role and toxicity of aluminium in specific biological functions have been getting significant attention in recent years. The interaction of aluminium and the living system is unavoidable due to its high earth crust abundance, and the long-term exposure to aluminium can be fatal for life. The adverse Al3+ toxicity effects in humans result in various diseases ranging from cancers to neurogenetic disorders. Several Al3+ ions sensors have been developed over the past decades using the optical responses of synthesized molecules. However, only limited numbers of water-soluble optical sensors have been reported so far. In this review, we have confined our discussion to water-soluble Al3+ ions detection using optical methods and their utility for live-cell imaging and real-life application.

Biphenyl Containing Amido Schiff base Derivative as a Turn-on Fluorescent Chemosensor for Al3+ and Zn2+ ions

A hydrazine derived Bis(2-hydroxybenzylidene)-[1,1'-biphenyl]-2,2'-dicarbohydrazide (sensor 1) has been synthesized and its sensing properties towards metal ions has been demonstrated using simple UV-visble spectroscopic, fluorometric technique and visible colour change. The...

The fluorescence turn-off mechanism of a norbornene-derived homopolymer – an Al3+ colorimetric and fluorescent chemosensor

A norbornene-derived hydrazone polymer was developed for high selectivity, and to be used as an effective colorimetric and fluorescent chemosensor of Al³⁺ in aqueous solutions.

Theoretical Investigations on the Excited-State Dynamics of an Al3+ Fluorescence Sensor

Twisted internal charge transfer (TICT) states are of fundamental importance during the photo-physical processes of dyes and sensors. In this contribution, excited-state dynamics of an Al³⁺ fluorescence sensor 1-{[(2-hydroxyphenyl)-imino]methyl}naphthalen-2-ol based on the turn-on signal is clarified. Two different dark TICT states are observed by exploring the excited-state potential energy surface. With the twist of the C2-N bond, the two dark states can be reached facilely, which induce the experimentally observed weak fluorescence of the sensor. The sensing mechanism is then uncovered by investigating the electronic coupling between the sensor and analyte. Al³⁺ is proved to form strong coordination bonds with the sensor, which restricts the motion of the C2-N bond. Consequently, the TICT states are eliminated, which generate the turn-on signal. This sensing mechanism is trustworthy and intrinsically different from the previously proposed one, which would shed some light on the design of turn-on sensors.

Highly selective and sensitive chemosensor for Al(III) based on isoquinoline Schiff base

As a colorimetric and fluorescent turn-on sensor to Al³⁺, N'-(2-hydroxybenzylidene)isoquinoline-3-carbohydrazide (HL) has been easily synthesized. The fluorescence intensity increases by 273 times in the presence of Al³⁺ at 458 nm. Meanwhile, the experiment data indicate that the limit of detection for Al³⁺ is 1.11 × 10^-9 M. Remarkably, the blue fluorescence signal of HL-Al³⁺ could be specially observed by the naked eye under UV light and is significantly different from those of other metal ions. Fluorescence switch based on the control of Al³⁺ and EDTA proved HL could act as a reversible chemosensor. According to ESI-MS result and the Job's plots, the 2:1 coordination complex formed by HL and Al³⁺ could be produced. Density functional theory calculations were performed to illustrate the structures of HL and complex. The cell imaging experiment indicates that HL can be applied for monitoring intracellular Al³⁺ levels in cells.

Estimation of Photophysical and Electrochemical Parameters of Bioactive Thiadiazole Derivative

The absorption and fluorescence spectra of synthesized 4-[5-(2,5-Dimethyl-pyrrol-1-yl)-[1, 3, 4] thiadiazol-2-ylsulfanylmethyl]-6-methoxy-chromen-2-one (DTYMC) compound were recorded in various solvents like acetone, acetonitrile, chloroform, dimethyl formamide (DMF),1,4-dioxane, ethanol, ethyl acetate, methanol, tetrahydrofuran (THF) and dimethylsulphoxide (DMSO) at room temperature in order to estimate the ground and excited state dipole moment. The ground state dipole moment (μ_g) and excited state dipole moment (μ_e) were calculated using solvatochromic shift method which involve equations proposed by Lippert, Bakshiev and Kawski-Chamma-Viallete. The results were signified that the excited state dipole moment is greater than the ground state dipole moment, which indicates the excited state is more polar than the ground state of the molecule. The bond angle between the ground state and excited state dipole moments were found to be 0⁰, The change in dipole moment (∆μ) was calculated using microscopic solvent polarity parameter ([Formula: see text]). Further multiple linear regression analysis of Kamlet-Taft parameter, HOMO-LUMO energy were determined by cyclic voltammetry using phosphate buffer solution.

Experimental and Theoretical Studies on a Simple S-S-Bridged Dimeric Schiff Base: Selective Chromo-Fluorogenic Chemosensor for Nanomolar Detection of Fe2+ & Al3+ Ions and Its Varied Applications

A simple S-S (disulfide)-bridged dimeric Schiff base probe, L, has been designed, synthesized, and successfully characterized for the specific recognition of Al3+ and Fe2+ ions as fluorometric and colorimetric "turn-on" responses in a dimethylformamide (DMF)-H2O solvent mixture, respectively. The probe L and each metal ion bind through a 1:1 complex stoichiometry, and the plausible sensing mechanism is proposed based on the inhibition of the photoinduced electron transfer process (PET). The reversible chemosensor L showed high sensitivity toward Al3+ and Fe2+ ions, which was analyzed by fluorescence and UV-vis spectroscopy techniques up to nanomolar detection limits, 38.26 × 10-9 and 17.54 × 10-9 M, respectively. These experimental details were advocated by density functional theory (DFT) calculations. The practical utility of the chemosensor L was further demonstrated in electrochemical sensing, in vitro antimicrobial activity, molecular logic gate function, and quantification of the trace amount of Al3+ and Fe2+ ions in real water samples.

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 simple turn-on ESIPT and PET-based fluorescent probe for detection of Al3+ in real-water sample

Aluminum is known as the most ubiquitous metal in earth's crust but its excessive exposure will cause damage to environment and health of the organism. Here, a turn-on Schiff base fluorescence probe STH based on excited state intramolecular proton transfer and photoelectron transfer processes for Al³⁺ detection with fast response rate (within minutes), low detection limit (4.26×10^-8M), high selectivity and reasonable pH application range (5.0-8.0) was developed. Fluorescence titration experiments show that probe STH has an excellent linear relationship (R²=0.9694) with Al³⁺ concentration and could be applied to quantitatively recognize Al³⁺ in real-water samples. Based on Job's plot and in situ mass spectra, two STH molecules will complex with Al³⁺ to form 2:1 complexation with oxygen atoms of hydroxyl and carbonyl groups and nitrogen atom of CN bond participating in coordination.

Coumarin-Based Small-Molecule Fluorescent Chemosensors

Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

A Highly Selective Turn-on Fluorescent Probe for the Detection of Aluminum and Its Application to Bio-Imaging

Aluminum is the most abundant metallic element in the Earth's crust and acts as a non-essential element for biological species. The accumulation of excessive amounts of aluminum can be harmful to biological species. Thus, the development of convenient and selective tools for the aluminum detection is necessary. In this work, a highly selective aluminum ion fluorescent probe N'-(2,5-dihydroxybenzylidene)acetohydrazide (Al-II) has been successfully synthesized and systemically characterized. The fluorescence intensity of this probe shows a significant enhancement in the presence of Al³⁺, which is subject to the strong quench effects caused by Cu²⁺ and Fe³⁺. The binding ratio of probe-Al³⁺ was determined from the Job's plot to be 1:1. Moreover, the probe was demonstrated to be effective for in vivo imaging of the intracellular aluminum ion in both living Drosophila S2 cells and Malpighian tubules.

A high performance 2-hydroxynaphthalene Schiff base fluorescent chemosensor for Al3+ and its applications in imaging of living cells and zebrafish in vivo

Developing high performance fluorescent chemo-sensors for in vitro and in vivo Al³⁺ detection is highly desirable, because Al³⁺ accumulation has been involved to various diseases. Herein, we report a highly selective and sensitive Schiff base fluorescent probe, H₃L, based on 2-hydroxynaphthalene, which can recognize aluminum ions and exhibit an "off-on" mode with high selectivity in methanol solutions. The detection limit of the probe for Al³⁺ is as low as 10^-7 M which was determined by fluorescent titration. The high selectivity and high sensitivity of H₃L for Al³⁺ are attributed to the inhibition of ESIPT. Additionally, the distribution of intracellular Al³⁺ ions could be observed under confocal fluorescence microscopy. Moreover, we also applied H₃L for in vivo detection of Al³⁺ ions in living zebrafish larvae.

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 highly selective colorimetric and fluorescent chemosensor for Al(III) based-on simple naphthol in aqueous solution

A colorimetric and fluorescent chemosensor (L) for Al(III) was synthesized and fully characterized. L could be both used as a colorimetric and fluorescent chemosensor for the detection of Al(3+) ions with low detection limit (8.87×10(-7) M) in CH3CN-H2O (1:1, v/v) solution. The binding ratio of L-Al(3+) was determined from the Job plot (absorption and fluorescence spectra) and MALDI-TOF MS data to be 1:1. The binding constant (Ka) of Al(3+) binding to L was calculated to be 4.8×10(5) M(-1) from a Benesi-Hildebrand plot. Moreover, the binding site of L with Al(3+) was determined by (1)H NMR titration experiment.

Selective interactions of trivalent cations Fe³⁺, Al³⁺ and Cr³⁺ turn on fluorescence in a naphthalimide based single molecular probe

Synthesis and fluorescence turn-on behavior of a naphthalimide based probe is described. Selective interactions of trivalent cations Fe(3+), Al(3+) or Cr(3+) with probe 1 inhibit the PET operating in the probe, and thereby, permit the detection of these trivalent cations present in aqueous samples and live cells. Failure of other trivalent cations (Eu(3+), Gd(3+) and Nb(3+)) to inhibit the PET process in 1 demonstrates the role of chelating ring size vis-à-vis ionic radius in the selective recognition of specific metal ions.

Design-specific mechanistic regulation of the sensing phenomena of two Schiff bases towards Al3+

We report herein two optical probes (R1 and R2) for the fluorogenic detection of Al³⁺ at the level of 10⁻⁸ M.

A highly selective fluorescent sensor for the detection of Al3+ and CN− in aqueous solution: biological applications and DFT calculations

A new turn-on fluorescent chemosensor 1 was developed to detect both Al³⁺ and CN⁻ and used for practical and biological applications.

Double-mode detection of HClO by naked eye and concurrent fluorescence increasing in absolute PBS

A fluorescent probe WCN for double-mode detection of HClO by naked eye and concurrent significant fluorescence increasing in absolute PBS.

A sensitive colorimetric and ratiometric chemosensor for trivalent metal cations

A novel hydroxyethyl piperazine functionalized cyanine derivative was designed and synthesized. It presents selective colorimetric as well as ratiometric absorption responses to trivalent metal cations (Cr(3+), Fe(3+) and Al(3+)) over a variety of divalent and monovalent metal cations in 3:7 ethanol-water solution. Detection limits of this method for Cr(3+), Fe(3+) and Al(3+) were 3.99 μM, 4.30 μM and 1.85 μM, respectively. The recognition mechanism was attributed to the protonation of the organic probe, which blocked the photoinduced electron transfer (PET) process. In addition, the sensor was also successfully applied to the determination of Cr(3+) in prepared samples.

A polynuclear hetero atom containing molecular organic scaffold to detect Al3+ ion through a fluorescence turn-on response

A simple polynuclear hetero atom (N and O) containing molecular organic scaffold/probe, 3 has been designed and synthesized and explored as a potential chemosensor to detect Al³⁺ (22 nM; ∼0.6 ppb) ion in a HEPES buffer.

A fast-responsive mitochondria-targeted fluorescent probe detecting endogenous hypochlorite in living RAW 264.7 cells and nude mouse

A very fast-responsive fluorescent probe for imaging mitochondrial ClO⁻was prepared. The probe was successfully applied in the imaging of endogenous ClO⁻in the mitochondria of RAW 264.7 cells and living nude mouse.

A quinoline based Schiff-base compound as pH sensor

A new Schiff-base compound, 1,4-bis-(quinolin-6-ylimino methyl)benzene (BQB), has been explored as reversible ratiometric fluorescence pH sensor.

Two fluorescent Schiff base sensors for Zn2+: the Zn2+/Cu2+ion interference

While theenol-iminetautomer inL1exhibits Zn²⁺/Cu²⁺ion interference, theketo-enaminetautomer inL2recognizes only Zn²⁺.

A novel turn-on Schiff-base fluorescent sensor for aluminum(iii) ions in living cells

Quinoline Schiff base L exhibits a more than 38-fold fluorescence enhancement after addition of Al³⁺ ions at an excitation wavelength of 373 nm, and shows a high selectivity for Al³⁺ over other metal ions.

A colorimetric and ratiometric fluorescent probe for ClO−targeting in mitochondria and its application in vivo

A colorimetric and ratiometric fluorescent probe PMN–TPP for imaging mitochondrial ClO⁻was prepared. The probe performed well in detecting ClO⁻in the mitochondria of living RAW264.7 macrophage cells and a living nude mouse.

Water-soluble host–guest system from β-cyclodextrin as a fluorescent sensor for aluminium ions: synthesis and sensing studies

In this paper, a simple small molecule (L) derived from 4-(diethylamino)-2-hydroxy-benzaldehyde and carbohydrazide has been synthesized, and a water-soluble host–guest system from β-cyclodextrin and L was obtained that exhibited characteristic fluorescence behavior toward Al³⁺.

FRET based ‘red-switch’ for Al3+ over ESIPT based ‘green-switch’ for Zn2+: dual channel detection with live-cell imaging on a dyad platform

Our designed chemosensor, rhodamine-HBT-dyad (RHD), selectively detects two biologically important ions (Al³⁺ and Zn²⁺) at two different wavelengths (red and green, respectively) through FRET and ESIPT in vitro and in vivo.

A rhodamine derivative as a highly sensitive chemosensor for iron(iii)

A novel rhodamine-based fluorescent probe P1 was synthesized for the optical detection of Fe³⁺. This fluorescent probe was proved to be effective for detecting Fe³⁺ in living cells and zebrafish.