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A “Turn-On” Fluorescent Probe for Detection and Removal of Zn2+ in Aqueous and its Application in Living Cells
Abstract
Using 3-hydroxy-2-naphthoic acid hydrazine and 4-(diethylamino) salicylaldehyde
as raw materials, compound L with an acylhydrazones structure was synthesized. The structure of compound L was characterized by nuclear magnetic resonance spectroscopy, X-ray single crystal diffraction, Fourier transform infrared spectroscopy, and mass spectrometry. The results show that Compound L can quickly and selectively recognize zinc ions in the H2O/DMSO (V:V=3:7) solvent system. After that, the spectral performance of probe L was studied by fluorescence spectroscopy and UV-vis spectroscopy. The results show that the combination with Zn²⁺ can significantly enhance the fluorescence intensity of probe L while being almost unaffected by other coexisting ions. After that, Job’s curve method, nuclear magnetic titration analysis, and mass spectrometry were used to study the binding mechanism of probe L and Zn²⁺. The results showed that probe L coordinated with Zn²⁺ is 1:1. The linear equations of different concentrations of Zn²⁺ and fluorescence intensity were obtained by fitting, and the detection limit of probe L for Zn²⁺ was determined to be 6.75×10⁻⁹ mol/L. The experimental study of standard addition and recovery showed that probe L could be used for the quantitative detection of Zn²⁺ in natural water samples. After that, we prepared L-doped sodium alginate hydrogel (SAL). The research results show that SAL has obvious adsorption capacity for Zn²⁺ in solution, and the color change before and after adsorption can be easily distinguished by the naked eye under ultraviolet light. SEM-EDS study showed that the microscopic morphology and composition of SAL changed significantly before and after adsorption. This fluorescent probe can be used for detection and removal of Zn²⁺ in aqueous solution. Also, probe L is effective for sensing for zinc (II) in living tumor cells. Overall, this work allows us to obtain a great potential to be applied to detect and remove Zn²⁺.
... Wang et al. synthesized probe 9 involved in the introduction of naphthalene group on salicylaldehyde group [50]. This probe exhibited specific detection of Zn 2+ through fluorescence enhancement at 510 nm, without any interference from other metal ions. ...
Zinc(II) ions (Zn2g) play crucial roles in the growth, propagation, and metabolism of animals, plants, and humans. Abnormal concentrations of Zn²⁺ in the environment and living organisms pose potential risks to environmental protection and human health. Therefore, it is imperative to develop rapid, reliable and in-situ detection methods for Zn2+ in both environmental and biological contexts. Furthermore, effective analytical methods are required for diagnosing diseases and understanding physiological metabolic mechanisms associated with Zn²⁺ concentration levels. Organic small-molecule fluorescent probes offer advantages such as fast, reliable, convenient, non-destructive detection capabilities and have significant application potential in Zn²⁺ detection and bioimaging; thus garnering extensive attention. Over the past two years alone, various organic small-molecule probes for Zn²⁺ based on different detection mechanisms and fluorophores have been rapidly developed. However, these probes still exhibit several limitations that need further resolution. In light of this context, we provide a comprehensive summary of the detection mechanisms, performance characteristics, and application scope of Zn²⁺ fluorescence probes since year 2022 while highlighting their advantages. We also propose solutions to address existing issues with these probes and outline future directions for their advancement. This review aims to serve as a valuable reference source offering insights into the development of advanced organic small-molecule-based fluorescence probes specifically designed for detecting Zn²⁺.
A fluorescence probe (Probe-ITR) was designed and synthesized for the rapid detection of Zn²⁺ based on the excited state intramolecular proton transfer (ESIPT) mechanism. The specific recognition ability of Probe-ITR to Zn²⁺ was tested using UV-VIS and fluorescence emission spectroscopy. The results demonstrated a rapid response within 40s upon addition of an appropriate amount of Zn²⁺ into the mixed solution of the target probe molecules (DMSO/PBS = 5/5). Under 365 nm ultraviolet light irradiation, the colorless solution changed to yellow-green fluorescence with a 150-folds increase in intensity. Furthermore, the detection limit for specific recognition of Zn²⁺ by the probe molecule is only 17.3 nmol/L, indicating high sensitivity. The practical application potential of the probe molecules was enhanced by employing on information storage and conducting cell imaging experiments.
A fluorescence probe ( Probe-Zn ) was designed and synthesized for the rapid detection of Zn ²⁺ based on the excited state intramolecular proton transfer (ESIPT) mechanism. The specific recognition ability of Probe-Zn to Zn ²⁺ was tested using UV-VIS and fluorescence emission spectroscopy. The results demonstrated a rapid response within 40s upon addition of an appropriate amount of Zn ²⁺ into the mixed solution of the target probe molecules (DMSO/PBS = 5/5). Under 365 nm ultraviolet light irradiation, the colorless solution changed to yellow-green fluorescence with a 150-folds increase in intensity. Furthermore, the detection limit for specific recognition of Zn ²⁺ by the probe molecule is only 17.3 nmol/L, indicating high sensitivity. The practical application potential of the probe molecules was enhanced by employing on information storage and conducting cell imaging experiments.
The Schiff base fluorescent probe (Dz-Jul), containing julolidine aldehyde and dansyl hydrazine, was derived using a simple condensation. This chemosensor showed high selectivity towards Zn²⁺ and quick response (170 s) in DMSO/H2O solutions (8/2, v/v, pH 7.2 buffer). A fluorometric titration determined that Dz-Jul-Zn²⁺ has a binding ratio of 1:1, and the association constant (Ka) is 1.03 × 10⁵ M⁻¹. The Dz-Jul detection limit of Zn²⁺ ions was 15 nM, much lower than the WHO standard (76.0 nM). DFT, ESI mass, and FTIR spectral demonstrated a plausible complexation mode between Dz-Jul and Zn²⁺ ions. In actual water samples, Zn²⁺ has been detected with good detection performance using Dz-Jul. Additionally, Dz-Jul-coated test strips allowed for rapid and qualitative monitoring of Zn²⁺ ions in a visible manner.
Graphical Abstract
In the past few decades, zinc has received great attention towards the scientific community due to its supreme importance in living organisms. Zinc is a trace element that is vitally important to all living organisms and it plays an important role in the immune system, wound healing, growth and division. Therefore, the development and advancement of simple, efficient, selective and inexpensive chemosensors for the determination of Zn2+ is of paramount prerequisite. Chemosensors have unique properties that are used for the determination of several metal ions specifically and selectively. This review summarizes the Schiff base chemosensors designed and synthesized by several research groups from the year 2018. The interaction of these probes with zinc metal ions has also been discussed briefly in this review. Furthermore, the comparison of detection limits of these probes demonstrated that the Schiff base probe 34 possessing two benzothiazole moieties exhibits the lowest detection limit (0.00028 µM) indicating it to be the lead compound in the determination of Zn2+ ions in near future.
Construction of fluorescent probes for zinc ion (Zn2+ ) and cadmium ion (Cd2+ ) is significant for the safety of humans. However, the discriminating recognition of Zn2+ and Cd2+ by a single probe remains challenging owing to their similar properties. Herein, a novel deoxycholic acid derivative containing 8-hydroxyquinoline fluorophore has been facilely synthesized through click chemistry to form a clamp-like probe. Using its perfect bonding cavity from 1,2,3-triazole and quinoline, this molecule showed favorable solvent-dependent fluorescent responses and distinguished Zn2+ and Cd2+ in different solvents. In ethanol aqueous solution, it displayed good selectivity and ratiometric fluorescence to Zn2+ with 30 nm spectroscopic red-shifts. In acetonitrile aqueous solution, it exhibited good selectivity and ratiometric fluorescence to Cd2+ with 18 nm spectroscopic red-shifts. Moreover, the unique microstructural features of the probe in assembly were used to reflect its recognition processes. Due to its merits of low detection limit and instant response time, the probe was utilized for sensing Zn2+ and Cd2+ in water, beer and urine with high accuracy. Meanwhile, this probe served as a handy tool and was employed to obtain inexpensive test strips for the prompt and semiqualitative analysis of Zn2+ and Cd2+ with the naked eye.
The sensing mechanism of the quinoline-derived Schiff base HL (concentrated from 8-hydroxyquinoline with 2,4-dihydroxybenzaldehyde) as a highly selective fluorescent probe for Zn²⁺ was investigated by theoretical calculations with DFT and TDDFT. The conformations of the HL molecule, its ketone from and its Zinc complex structure, were optimized in the ground and excited states. The systems have been studied in depth in terms of structural parameters, frontier molecular orbitals, absorption and fluorescence spectra as well as potential energy curves analysis and approximately density gradient analysis. The present theoretical calculations propose a different detection mechanism from that proposed experimentally. The theoretical results predict that the fluorescence quenching in HL is attributed to the excited state intramolecular proton transfer (ESIPT) rather than the photoinduced electron transfer (PET) of benzene to electrons. When Zn²⁺ is introduced, Zn²⁺ takes the place of the H atom, creating a complex that blocks the ESIPT reaction and restores fluorescence.
Herein, we have synthesized two unsymmetrical and dipodal Schiff–Mannich combo ligands, benzoic acid (3–benzoimidazol–1–ylmethyl–2–hydroxy–5–methyl–benzylidene)–hydrazide (H2BBH) and the hydroxyl analogue, 2–hydroxy–benzoic acid (3–benzoimidazol–1–ylmethyl–2–hydroxy–5–methyl–benzylidene)–hydrazide (H3BSH) for selective detection of Zn2+ in semi–aqueous medium. Both the probes selectively depict a turn–on response to Zn2+ as a result of combined effect of chelation–induced enhanced fluorescence (CHEF) and photo–induced electron transfer (PET). Detailed experimental studies reveal that H2BBH and H3BSH can detect Zn2+ in solution with limit of detection 27 nM and 46 nM respectively. The structures of probe–Zn2+ ensembles have been proposed as [(HBBH)2Zn] and [(H2BSH)2Zn] by ESI–MS, FT–IR, 1H NMR titration and DFT/TD–DFT methods. Moreover, both the probes have been successfully employed in the detection of Zn2+ in HuH–7 cell, seedling of chickpea and mung beans, and paper strips.
A Schiff base fluorescent probe compound H2L (N′‐(4‐bromo‐2‐hydroxy‐benzylidene)‐3‐hydroxy‐2naphthohydrazide) was synthesized using 3‐hydroxy‐2‐naphthoic acid hydrazide as raw material. The structure of H2L was characterized by NMR, IR, MS, and XRD methods. The fluorescence performance of H2L was studied by UV and FS. The results show that in 1 : 4 water system /DMSO solution (water system: 20 % triethanolamine:0.1 mol/L L‐cysteamine acid=1 : 1), H2L can be used to quickly identify Mg²⁺ with an obvious fluorescence enhancement and redshift. A color change “light green→bright yellow” can be clearly observed with the naked eye. The Mg²⁺ concentration shows a good linear relationship in the range of 0–1.0×10⁻⁵ mol/L, with a detection limit of 1.77×10⁻⁷ mol/L with good stability and reversibility. The response mechanism was explored through Job's curve, NMR titration and MS, which showed that Mg²⁺ can form a 1 : 1 complex with H2L. A gel (SAL) was prepared by doping H2L into sodium alginate (SA). SAL was found to show good adsorption properties for Mg²⁺ and can be easily distinguished by the naked eye under ultraviolet light. The microscopic morphology and composition of SAL before and after Mg²⁺ adsorption were analyzed by SEM‐EDS. H2L can be used for the qualitative detection of Mg²⁺ in actual water samples without being affected by other common metal ions, and has potential application value in the field of environmental detection.
Viscosity has become increasingly important in biological systems, especially as a major factor in the process of diffusion control. The abnormality of viscosity is closely related to the development of many diseases in the cellular microenvironment. The abnormal viscosity behavior of cells is always accompanied with dramatic changes in the levels of relevant active analytes. Therefore, real-time monitoring of local microviscosity and analytes changes in living cells is of great importance. In comparison to conventional imaging approaches, fluorescence imaging has become a powerful tool to detect microenvironments and analytes in living systems as a result of its excellent sensitivity, non-invasive detection, high selectivity and real-time imaging. For the first time, in this review, we focused on the design strategies, spectral performance, and biological applications of multifunctional probes for the simultaneous detection of viscosity and analytes which were reported in recent years. We categorized and discussed the limitations of the present multifunctional probes, proposed new ideas to overcome and change these limitations. We hope this review will provide new research directions for the development of multifunctional probes, which will contribute to the early diagnosis and treatment of diseases, the development and delivery of new drugs.
A novel Schiff base fluorescent probe (N'-(4-(diphenylamino)benzylidene)-3-hydroxy-2-Naphtho-hydrazide)(L) was designed and synthesized using 3-hydroxy-2-naphthoic acid hydrazide and 4-diphenylaminobenzaldehyde as raw materials. The structure of L was characterized through ¹H NMR, ¹³C NMR, HR-MS, IR and X-ray. The study found that probe L showed high sensitivity and selectivity response to copper ions(Cu²⁺) in H2O/DMSO(V:V=3:7, pH=7) solution. The possible mechanism of coordination between L and Cu²⁺ was studied by HR-MS, ¹H NMR and DFT calculation. PAML was prepared by the method of doping L into polyacrylamide(PAM). PAML had high adsorption of Cu²⁺ and the removal rate of Cu²⁺ by PAML in water reached 96.99%, in addition, the color change could be distinguished by naked eyes under UV lamp. The microscopic morphology of PAML before and after adsorption of Cu²⁺ was observed by SEM-EDS.
In the present study, the design of a novel turn–on fluorescent probe ((E)–5–methoxy–4–((thiazol–2–ylimino)methyl)benzene–1,3–diol) (TBD) was reported. TBD showed an excellent fluorogenic response (λex=420 nm, λem=530 nm) to sense Zn²⁺ in HEPES buffer/MeCN (5/95, v/v; pH=7.4) media. The quantum (Φ) yield of the probe TBD increased importantly with Zn²⁺ and was calculated for TBD (Φ=0.073) and TBD–Zn²⁺ complex (Φ=0.78). The LOD and binding constant (Ka) of TBD were 1.29 nM and 1.102×10⁶ M–1, respectively. The sensing process of TBD toward Zn²⁺ (1:1) was verified by the Job's plot, MALDI–TOF–MS, and ¹H–NMR titration studies. The ''off–on'' fluorogenic response of TBD was qualified to the photo–induced electron transfer (PET) process. The experimental outcomes were also verified by theoretical DFT studies. Furthermore, TBD had been successfully utilized to detect Zn²⁺ in food supplement products, drinkable water samples and living–cells for on–site analysis.
A water-stable luminescent Zn-MOF [Zn2(IDS)(bipy)1.5] (complex 1) (H4IDS = meso-iminodisuccinic acid, bipy = 4,4’-bipyridine) was successfully synthesised by hydrothermal method through in-situ formation of a meso-iminodisuccinic acid ligand from two l-aspartic acid precursors. Complex 1 presents a structure with crs architecture and a topological point symbol of {3⁶.6⁶.7³}. It is found that complex 1 can selectively and sensitively detect Fe³⁺ and 2,4,6-trinitrophenol (TNP) by luminescence quenching in aqueous solution. The quenching constant (Ksv) for Fe³⁺ is 1.39 × 10⁴ M⁻¹ with the detection limit (LOD) of 3.93 × 10⁻⁵ M; and the Ksv for TNP is 2.6 × 10⁴ M⁻¹ with the LOD of 6.47 × 10⁻⁵ M. In particular, as the concentration of TNP increases, the red shift (about 23 nm) of emission spectra can also be obviously monitored. The mechanism of complex 1 to Fe³⁺ is due to inner filtration effect (IFE) and the interaction with uncoordinated oxygen atoms of the framework, while to TNP is because of IFE and fluorescence resonance energy transfer (FRET).
A new benzothiazole-based fluorescent chemosensor (BZDM), namely 2-amino-3-(((E)-3-(benzo[d]thiazol-2-yl)-2-hydroxy-5-methylbenzylidene)amino)maleonitrile, has been designed and synthesized for detection of Al³⁺/Zn²⁺ in aqueous medium. The sensing behavior displayed that BZDM possessed an excellent selectivity towards Al³⁺/Zn²⁺ with a distinct fluorescence enhancement in DMSO/Tris-HCl buffer solution. The binding stoichiometry was determined to be 1: 1 between BZDM and Al³⁺/Zn²⁺ according to Job’s plot method and NMR analysis. The sensing of Al³⁺/Zn²⁺ was almost free from interference of other relevant metal ions. Under optimal conditions, the LOD value for Al³⁺ and Zn²⁺ was found to be 7.06 μM and 2.98 μM, separately. Notably, the probe was found to have good biological compatibility and was employed to detect Al³⁺/Zn²⁺ in living Hela cells.
Zinc ion is the 2nd abundant transition metal element in human's body. It is responsible for many physiological and biological functioning in the body, such as growth of people, immunity, endocrine, etc. The deficiency of zinc could result in an increasing risk for growth retardation, neurological disorder and infectious disease. Thus, developing a nondestructive method for detecting Zn²⁺ in living systems is important. Here we reported a 2-(2-methyl-4H-ylidene)- malononitrile (DCM)-based NIR probe DF-Zn for selective and sensitive detection of Zn²⁺. The probe DF-Zn is cell-permeable and stable at broad pH range. DF-Zn showed a fast response to Zn²⁺, big stock's shift, and “nude-eye” recognition for Zn²⁺. Moreover, the selective binding of probe DF-Zn to Zn²⁺ was reversible. With the addition of EDTA in buffer solution, reversible response of probe to Zn²⁺ could be observed in MCF-7 cells imaging.
A pair of homologues, [Zn(Hssa)(1,4-bib)·H2O]n (1) and [Zn3(ssa)2(1,4-bib)3·4H2O]n (2), were successfully assembled using the same metals and ligands [H3ssa = 5-sulfosalicylic acid; 1,4-bib =1,4-bis(1H-imidazol-1-yl)benzene] under solvothermal conditions. Polymer 1 is a two-dimensional (2D) sql network and polymer 2 is a three-dimensional (3D) framework. Polymer 2 can be simplified into two topology types: bct and tfc. The two polymers show significant differences in the fluorescence sensing of metal ions and proton conductivity. Their applications in detecting metal ions and proton conductivity were explored. Polymer 1 shows high sensitivity and selectivity for Fe³⁺, while polymer 2 can detect Hg²⁺ ions. The limit of detection was 1.66 μM with Fe³⁺ for 1 and 0.23 μM with Hg²⁺ for 2 in water. In addition, both 1 and 2 exhibit high water stability and proton conductivity. At 60 °C and 95% relative humidity, their conductivities were 3.45×10-5 and 6.26×10-6 S cm⁻¹, respectively. A detailed analysis of the Hirshfeld surface and fingerprints was carried out for 1 and 2 to compare interactions between the molecules, which is essential for analysing the relationships between their structures and material properties.
A bis (thiosemicarbazone) based probe has been synthesized and structurally characterized. The probe exhibits good selectivity towards Zn(II), Cd(II) and Hg(II) ions in an aqueous solution containing 95% water with ratiometric fluorescence changes. The modes of coordination of the probe with these metal ions and binding properties have been examined using different spectral techniques. The binding constants, determined using fluorescence titration data, are found to be 9.8 × 10³, 1.39 × 10⁵ and 2.03 × 10¹³ M⁻¹, respectively for Zn(II), Cd(II) and Hg(II) complexes. The high sensitivity of the probe has been demonstrated by the very low limit of detection i.e. 5.1, 3.4 and 0.51 μM for Zn(II), Cd(II) and Hg(II) ions, respectively. Different coordination mode of these metal ions with the probe has resulted in varying intra-ligand fluorescence (λem nm, Zn(II): 488, Cd(II): 470 and Hg(II): 578) among these metal complexes.
A newly designed and synthesized half condensed organic moiety 2-hydroxy-5-methyl-3-[(2-phenylamino-phenylimino)-methyl]-benzaldehyde (HL′) and the Zn2L4 complex sequentially detects the Zn2+ and H2PO4− ions as low as 1.13 nM and1.23 M respectively. HL′and dinuclear Zn(II) complex of in situ generated L- in solution formulated as Zn2L4 under investigation have been characterized by physicochemical and spectroscopic studies along with detailed structural analyses using single crystal X-ray crystallography. The selectivity and sensitivity of HL' towards Zn2+ ion and of Zn2L4 complex towards H2PO4− ions are based on CHEF and through displacement pathways, respectively. Dual sensing of Zn2+ ion and H2PO4-ions in aqueous medium via “Green-Blue-Green” emission with the reversible transformation of in situ formed HL′ to HL is established by detailedelectronic absorption and emissionspectroscopic studies. This non-cytotoxic probe (HL′ i.e. produced HL in solution) and Zn2L4 complexes are able to monitor the subcellular distribution changes of Zn2+ and H2PO4− ions respectively by fluorescence microscopy using the human semen sample.
Remediation of heavy metal contaminated soils remains a global challenge. Here, low-molecular-weight organic acids were used to extract Cu and Zn from polluted soils, and the extracted heavy metals were subsequently adsorbed by activated carbon electrodes. The electrochemical adsorption mechanism as well as the influence of pH, organic acid type and voltage were investigated, and the soil remediation effect was further evaluated by the cultivation of rape. After extraction by citrate at initial pH 8.3 and electrochemical adsorption at 0.9 V for 7 d, the concentrations of total and bioavailable Cu in soils decreased from 1090 to 281 to 391 and 52 mg kg⁻¹, and those of Zn decreased from 262 to 39 to 208 and 30 mg kg⁻¹, respectively. Cu and Zn ions were mainly electrochemically adsorbed on the carbon cathode and anode, respectively, resulting in decreases of their concentrations to below 1 mg L⁻¹ in the leachate. The presence of organic acids improved the remediation performance in the order of citrate > oxalate > acetate. The decrease in the initial pH of citrate solution enhanced the removal rate of Zn, while seemed to have no effect on that of Cu. The removal capacity for heavy metals decreased with decreasing cell voltage from 0.9 to 0.3 V. In the rape cultivation experiment, the Cu and Zn contents in shoot and root were decreased by more than 50%, validating the soil remediation effect. The present work proposes a facile method for heavy metal removal from contaminated soils.
As is known, Zn²⁺ plays a vital role in a variety of biological processes but excessive exposure of Zn²⁺ to human beings can cause toxicity, inducing a series of overt poisoning symptoms and neurodegenerative disorders. Thus, we designed and synthesized two quinoline-derived Schiff-bases HL1 and HL2, and investigated the fluorescence emission responses of these two Schiff-bases to various metal ions. A significant enhancement in fluorescence emission band centered at 450 nm was observed in the ethanolic solution of HL1 with addition of Zn²⁺, while remarkably lower fluorescence emission enhancement was obtained in the case of HL2 in which one methyl group was introduced to the azomethine carbon. In addition, HL1 showed good selectivity and high sensitivity towards Zn²⁺ in the existence of other various interfering metal ions, and the reversibility and regeneration of HL1 were also perfect for extending its applications in environmental and biological systems. Therefore, HL1 could be identified as a fluorescent probe for sensing Zn²⁺ environmentally and biologically.
Two novel rhodamine-polystyrene solid-phase fluorescence sensors PS-RB-2 and PS-R6G-2 with pyrene or naphthalene as fluorophore were synthesized for Hg(II) detection. Their structures were characterized by Fourier transform infrared (FTIR) spectra and scanning electron micrographs (SEM). Sensor PS-RB-2 displayed higher selectivity and sensitivity to Hg(II), with a lower detection limit of 0.065 μM. A detection mechanism involving the Hg(II) chelation-induced spirocycle open of rhodamine was proposed and discussed from theoretic level based on crystal structures and density functional theory (DFT) calculations. Sensor PS-RB-2 with recyclable and environment-friendly performance was successfully employed to fluorescent detection of Hg(II) in real water and fish samples, indicating its good potential in practical application. Its solid phase extraction columns were developed for rapid detection of Hg(II) by observing the color change with the naked eyes.
Intracellular nitroxyl (HNO) acts as an essential intermolecular signal to regulate a wide variety of physiological and pathological processes. Nondestructive detection of HNO in living cells is an urgent need for further study of its physiological activity. In this work, we have developed a new probe LJ-3 for HNO detection with simultaneous response in green and NIR channels. Probe LJ-3 exhibited fast, large Stock's shift and sensitive response to HNO along with a distinct fluorescence change with maximum emission peak at 520 and 673 nm. The limit of detection of probe LJ-3 for HNO was calculated to be 111.6 nM. Furthermore, imaging studies taken in HepG-2 cells showed that LJ-3 could be employed as a dual-channel fluorescent probe for endogenous HNO detection and imaging in living system.
Temperature-driven, highly sensitive and selective “TURN-ON” fluorometric detection of Zn²⁺ by benzothiazole-based probes (L¹ and L²) was reported in physiological pH in the present work. Iron(II) acted as the reversible switch or trigger for the reversible detection of Zn²⁺ ions by the probes resulting in “TURN-OFF” fluorescence at room temperature. However, selective detection of Zn²⁺ in the presence of Fe²⁺ was irreversible at 0–5 °C. Such temperature dependence on reversible fluorometric detection of Zn²⁺ in the presence of Fe²⁺ was explained from the thermodynamic perspective as well as DFT calculations in which the absolute enthalpy (H) and Gibbs free energy (G) of the resultant complexes and the fluorophores (L¹ and L²) at different temperatures were determined. Enhanced fluorescence of the Zn²⁺ bound probes was due to the inhibition of excited-state intramolecular proton transfer (ESIPT). Effect of solvents, pH, and temperature on the fluorometric detection of Zn²⁺ was also probed in the present work. The results were translated into the visual detection of Zn²⁺ on paper-based fluorescence probe and later we demonstrated the sensing of mobile Zn²⁺ ions by the probes in living HeLa cells as the proof of concept of our present investigations.
Graphic Abstract
A benzothiazole-based, “TURN-ON” fluorescent sensor was developed for selective and reversible detection of Zn²⁺in vitro, in which Fe²⁺ acted as the reversible switch. Open image in new window
A fluorescence-enhanced sensor based on aggregation-induced emission (AIE) was synthesized using a di(2-picolyl)amine (DPA) group as a highly selective metal chelating agent for Zn2+. The combination of the probe and Zn2+ was achieved in an environment where the volume fraction of water was 90%, giving the probe good biocompatibility, and a large Stokes shift (100 nm) occurred after Zn2+ was combined with the probe. The obvious color change makes the probe visible to the naked eye, and gives it a high signal-to-noise ratio, and high contrast, and minimizes self-absorption. Because of the high selectivity of the DPA group to Zn2+, the sensitivity of the probe to detect Zn2+ has been improved. The mechanism of the formation of complexes between the probe and Zn2+ was confirmed by nuclear magnetic resonance spectroscopy (NMR), high-resolution mass spectrometry (HRMS), and particle size distribution. Under the optimal experimental conditions, the linear fluorescence reaction of Zn2+ was good, between 0.2 and 18 μM, and the detection limit was 1.3 × 10−7 M. The low toxicity and excellent membrane permeability of the probe in living cells enable it to be efficiently applied for Zn2+ imaging in cells.
Graphical abstract
Early detection of probes is very important for limiting toxic effects of various transition metal ions for example aluminum and zinc. Monitoring of these metal ions can be challenging via conventional methods since they are high cost instrumentations, time consuming and so on. We report facile preparation of a fluorescence probe containing biphenyl groups that effectively selective and superb sensitivity towards aluminum (III) and zinc (II) in neutral solutions without interference from each other and other ions. In neutral pH value, the probe FOB displayed the OFF-ON fluorescence enhancement at 464 nm and 512 nm toward aluminum (III) and zinc (II), respectively. The detection limit values of FOB for Al3+ and Zn2+ in neutral solutions were 1.27 and 1.02 nM, respectively and these values were significantly lower than permitted Al3+ and Zn2+ concentrations in drinking water determined by the World Health Organization (WHO) and European Water Quality. Also, fabricated cyano-biphenyl based probe is effective for sensing for aluminum (III) and zinc (II) in living human colon cancer cells even when employed at low concentrations (1.0 μM). Overall, this work allows us to obtain a great potential to be applied to detect Al3+ and Zn2+.
A dual-function probe NAHH based on naphthalene was synthesized and characterized. Based on the combination effects derived from the inhabitation of photo-induced electron transfer (PET) and CN isomerization, probe NAHH achieved in the recognition of Zn2+ and Al3+ both through obvious fluorescence enhancement and color changes detected by naked eye, respectively. Probe NAHH showed high sensitivity with the limit of detection as low as 3.02 × 10-7 M for Zn2+ and 7.55 × 10-8 M for Al3+, indicated the capability of probe NAHH in trace detection for Zn2+ and Al3+. The binding ratio of NAHH with Zn2+ and Al3+ were all 1:1 determined by Job plot, and the corresponding association constant was calculated as 8.48 × 104 M-1 and 4.45 × 105 M-1, respectively. The mechanism was further confirmed by FT-IR, 1H NMR titration and ESI-MS analysis. Furthermore, probe NAHH was successfully applied in logic gate construction and the detection of Zn2+ and Al3+ in Songhua River and test stripe. Fluorescence imaging experiments confirmed that NAHH could be used to monitor Zn2+ in plant root.
As Al³⁺ is detrimental both to human and other organisms, a simple sensor, acylhydrazone AhzF, is synthesized in one step and its structure is confirmed by single crystal X-ray diffraction. AhzF shows specific fluorescence turn-on response for Al³⁺ over other metal ions at UV 365 nm, observed by naked-eyes. Its detection limit can reach to 1.11 × 10⁻⁹ M in ethanol. Meanwhile, AhzF at low concentration can detect Al³⁺ with excellent interference resistance to typical disturbing metal ions including Cu²⁺ and Fe³⁺. For the first time, concentration influence of Fe³⁺ during AhzF detecting Al³⁺ has been explored and it has been found that the fluorescence of AhzF-Al³⁺ is partly quenched by Fe³⁺ while with no influence by Cu²⁺ at high concentration (above 10⁻⁶ M), indicating its good low concentration advantage during Al³⁺ detection. The binding mode exhibits a 1:1 M ratio between AhzF and Al³⁺, which are confirmed by titration test, Job’s plot, ¹H NMR spectra and mass spectrum. It also exhibits good reusability by alternate addition of Al³⁺ and EDTA to the AhzF solution. The pH effect tests suggest its good sensitivity from pH 4 to pH 10 and AhzF can recognize labeled Al³⁺ in tap water directly by naked eyes, which makes it possible for the application in real environment.
Three enhanced fluorescence probes based on Rhodamine B-Schiff base structure were synthesized for detecting Cu²⁺. The corresponding detection limits were found to be 0.25 μM, 0.15 μM and 0.18 μM. Binding ratio and binding sites were determined by Job's and nuclear magnetic titration experiments. The binding constants obtained by the Benesi-Hildebrand equation to be 341.0 M−0.5,1.8 × 10⁴ M⁻¹, and 265.4 M−0.5, respectively. As isomers, the different effects of probes on Cu²⁺ detection were researched. By adjusting the position and the size of the substituent group, the effects of binding sites and steric hindrance on the complexation ratio, response time and detection limit were discussed. Optimal spatial combination structure with Cu²⁺ was obtained through energy calculation. Detection mechanism of Rhodamine B ring opening based on the complex of the Schiff base with Cu²⁺ was confirmed. E. coli staining and detection of real water samples had expanded their applications.
A new multi-analytes selective fluorescence chemosensor DA was synthesized by simple one pot reaction between dansyl chloride and 2-aminobenzohydrazide in the presence of base. In DMSO:H2O (1:1, v/v), the fluorescence of DA at 483 nm was blue shifted and enhanced at 474 nm along with a new shoulder peak appeared at 411 nm selectively in the presence of Cu2+ among the other tested metal ions due to the chelation enhanced fluorescence (CHEF) effect. Without any noticeable interference from potentially competitive metal ions, sensor DA can detect Cu2+ down to 9.79×10-7 M. Sensor DA gives satisfactory results for the quantification of Cu2+ in real water samples. Sequentially, the resultant in-situ generated DA-Cu2+ complex is applied for the selective sensing of bioactive cysteine with the detection limit down to 1.76×10-6 M.
Upon excitation of the visible light, probes show colorimetric and fluorescent responses to the specific metal ion, which can be easily detected by the naked eye. Owing to the excitation of the visible light at 423 nm, a novel and simple Schiff-base receptor based chromone derivative called 7-methoxychromone-3-carbaldehyde-(indole-3-formyl) hydrazone (MCIH2) had been investigated as a selective and sensitive probe for Al ³⁺ with colorimetric and fluorescent responses. Upon addition of Al ³⁺ to compound MCIH2 solution, compound MCIH2 could respond to Al ³⁺ with a good selective colorimetric signal, which was easily observed from colorless to yellow-green by the naked eye. Furthermore, a remarkable fluorescence emission enhancement with an “OFF-ON” signal by over 700-fold was triggered, but other various metal ions had no such significant effects on the fluorescence emission. In addition, the detection limit of compound MCIH2 for recognizing Al ³⁺ was evaluated to be as low as 1 × 10 ⁻⁷ M level, which was sufficiently low for sensing Al ³⁺ widely distributed in various environmental and biological systems.
Simple pyrene-based chemosensors 1 to 3, were synthesized from pyrene-1-carboxaldehyde and they were characterized using various spectroscopic techniques like UV–Vis, FT-IR, Mass, ¹ H NMR and ¹³ C NMR. Among synthesized receptors, the receptor 1 shows high selectivity towards Hg ²⁺ ions. Further, the high selectivity of receptor 1 towards Hg ²⁺ ions in the presence of various other interfering metal ions like Ni ²⁺ , Zn ²⁺ , Mn ²⁺ , Co ²⁺ , Cu ²⁺ , Cr ³⁺ , Fe ³⁺ , Al ³⁺ , Ag ⁺ , Fe ²⁺ , Cd ²⁺ , Mg ²⁺ , Pb ²⁺ , Ca ²⁺ , Na ⁺ , K ⁺ was confirmed by UV–Vis and fluorescence methods. The detection limit for Hg ²⁺ ions was found to be 0.270 μM. The chemodosimetric irreversible hydrolysis of the receptor 1 in the presence of Hg ²⁺ was studied by UV/Vis, fluorescence, FT-IR, LC-MS, ¹ H NMR and theoretical DFT study. Further, the real life applications of receptor 1 for the determination of Hg ²⁺ ions were demonstrated by UV–Vis method.
The development of acid environment-applicable fluorescence sensor is challenging but attractive topic, which can achieve the rapid and comprehensive evaluation of total soluble heavy metal content in natural water. In this work, a quinoline-containing Schiff base, AMQD, was utilized as fluorescence probe for Cd ²⁺ . Interestingly, the obtained chemosensor exhibited much better fluorescence detection sensitivity and selectivity toward Cd ²⁺ in acidic 10% methanol aqueous solution (pH 4) comparing to those in neutral environment. Initially, the fluorescence emission of AMQD was almost invisible with the absence of metal ions, while a significant turn-on fluorescence response (~425 nm) can be observed with the addition of Cd ²⁺ . The fluorescence detection possesses excellent selectivity without the interference of any other metal cation. The recognition ratio between the fluorescence sensor AMQD and Cd ²⁺ was confirmed to be 1:1, and the detection limit was calculated to be 2.4 nM.
A novel multifunctional sensing material (RSPT), incorporating rhodamine B hydrazide, Schiff-base and phenolic hydroxyl group into triazine, was identified and prepared. After the molecular structure was characterized by FTIR, 1H NMR, mass spectra and element analysis, it was noted to find that there were multichannel turn-on fluorescent responses to Zn2+ and Bi3+, i.e., a strong fluorescence emission at 483 nm in DMF-water (99/1, V/V) for Zn2+ with color change from colorless to light yellow-green, while an increased fluorescence emission at 580 nm in CH3CN-water (99/1, V/V) for Bi3+ with color change from colorless to red. Their different action mechanisms for RSPT-Zn2+ and RSPT-Bi3+ complexes were investigated and confirmed by means of fluorescent titration, binding constant, Job’s plot curve, 1H NMR titration and theoretical simulation. RSPT would be a promising turn-on fluorescent chemo-dosimeter for multichannel detection of Zn2+ and Bi3+ with a detection limit of 3.0 nmol•L−1 for Zn2+ and 8.6 nmol•L−1 for Bi3+, respectively.
2-Hydroxy-5-methyl-3-((quinolin-6-ylimino)methyl)benzaldehyde (HL) has been found to be a ratiometric fluorescent chemosensor for pH. It has been synthesized by Schiff-base condensation reaction between 4-methyl-2,6-diformylphenol and 6-aminoquinoline in 1:1 ratio in methanol and characterized by various standard methods. Fluorescence peak of it appears at 464 nm (excitation 360 nm) with strong intensity at low pH in Britton Robinson buffer. With the gradual increase in pH value of the medium, intensity at 464 nm decreases and a new peak emerges at 529 nm with gradual increase in its intensity. Fluorescence intensity of HL remains almost unaffected in the presence of different cations and anions both in acidic and basic media. Fluorescence intensity can be successively altered to its original value with cyclic change of pH between 4.0 and 10.0 indicating stability of the probe in both the media. pKa of HL has been determined to be 6.24. Colorless probe in strong acidic medium turns green in pH of ~ 6 or more under visible light. Under same condition, color changes from blue to green with the illumination of UV irradiation. These changes are handy to detect different pH medium and are in accordance with UV–vis spectral results. Phenolic proton of HL deprotonates in higher pH as is also evident from the theoretical calculations. This probe has been applied to detect pH regions using lemon juice and river (Ganga) water.
Two amido-schiff bases (3-Hydroxy-naphthalene-2-carboxylic acid pyren-1-ylmethylene-hydrazide and Naphthalene-2-carboxylic acid pyren-1-ylmethylene-hydrazide) have been synthesized having a common structural unit and only differs by a -OH group in the naphthalene ring. Both of them can detect Cu(2+) ion selectively in semi-aqueous medium in distinctly different output modes (one detects Cu(2+) by naked-eye color change where as the other detects Cu(2+) by fluorescence enhancement). The difference in the binding of Cu (2+) with the compounds is the reason for this observation. The detection limit is found to be micromolar region for compound which contains -OH group whereas the compound without -OH group detects copper in nano-molar region. DFT calculations have been performed in order to demonstrate the structure of the compounds and their copper complexes. Practical utility has been explored by successful paper strip response of both the compounds. The biological applications have been evaluated in RAW 264.7.
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 Al3 + ions with low detection limit (8.87 × 10- 7 M) in CH3CN-H2O (1:1, v/v) solution. The binding ratio of L-Al3 + was determined from the Job plot (absorption and fluorescence spectra) and MALDI-TOF MS data to be 1:1. The binding constant (Ka) of Al3 + binding to L was calculated to be 4.8 × 105 M- 1 from a Benesi-Hildebrand plot. Moreover, the binding site of L with Al3 + was determined by 1H NMR titration experiment.
A Eu-doped metal-organic framework (Uio-66-NH2-Eu) has been synthesized under an appropriate hydrothermal condition and used as a luminescence sensor for Cd2+ detection. Uio-66-NH2-Eu shows excellent luminescence and good fluorescence stability in water which performs a remarkable enhancement effect (∼13 times as much as original one) in the luminescence emission of Eu3+ upon the introduction of Cd2+. This is a better example for detecting Cd2+ in aqueous solutions based on a lanthanide functionalized metal-organic frameworks (MOFs). Most importantly, the luminescence probe of Cd2+ shows a low detection limit (0.22 μM), a broad linear range (0.22-500 μM), fast detection time (<5 min), and the signals can be observed by the naked eyes under the irradiation of UV light of 365 nm. Subsequently, Uio-66-NH2-Eu was developed as a highly selective and sensitive probe for detection of Cd2+ in aqueous solutions. This work may be provided a possibility for Cd-detection in other biological systems.
A new simple receptor 1 based on aminosalicylimine was prepared. It exhibited an 'off-on fluorescence type' mode with high sensitivity in the presence of Zn2+. In particular, this chemosensor could clearly distinguish Zn2+ from Cd2+. Also, it could be a reusable chemosensor because the addition of EDTA quenched the fluorescence of the Zn2+-2-1 complex. Furthermore, receptor 1 had a sufficiently low detection limit (68 nM) in aqueous solutions, which implies that 1 could sense the nanomolar concentration of Zn2+. Therefore, this sensor has the ability to be a practical system for the monitoring of Zn2+ concentrations in aqueous samples.
Dynamin is a key regulatory protein in clathrin mediated endocytosis. Compared to genetic or immunological tools, small chemical dynamin inhibitors such as dynasore have the potential to study the dynamic nature of endocytic events in cells. Dynasore inhibits dynamin GTPase activity and transferrin uptake at IC(50) approximately 15 microM but use in some biological applications requires more potent inhibitor than dynasore. Here, we chemically modified the side chains of dynasore and found that two derivatives, DD-6 and DD-11 more potently inhibited transferrin uptake (IC(50): 4.00 microM for DD-6, 2.63 microM for DD-11) and dynamin GTPase activity (IC(50): 5.1 microM for DD-6, 3.6 microM for DD-11) than dynasore. The effect was reversible and they were washed more rapidly out than dynasore. TIRF microscopy showed that they stabilize the clathrin coats on the membrane. Our results indicated that new dynasore derivatives are more potent inhibitor of dynamin, displaying promise as leads for the development of more effective analogues for broader biological applications.
The article focuses on adsorption of heavy metal ions on soils and soils constituents such as clay minerals, metal (hydr)oxides, and soil organic matter. Empirical and mechanistic model approaches for heavy metal adsorption and parameter determination in such models have been reviewed. Sorption mechanisms in soils, the influence of surface functional groups and surface complexation as well as parameters influencing adsorption are discussed. The individual adsorption behavior of Cd, Cr, Pb, Cu, Mn, Zn and Co on soils and soil constituents is reviewed.
Selective colorimetric chemosensor for the detection of Hg2+ and arsenite ions using Isatin based Schiff's bases; DFT Studies and Applications in test strips
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