Monoterpenoid derivative based ratiometric fluorescent chemosensor for bioimaging and intracellular detection of Zn2+ and Mg2+ ions

A bicarboxaminoquinoline-based ratiometric fluorescent sensor for the sequential detection of Zn2+ and PPi

A new ratiometric fluorescent sensor (LP) based on bicarboxaminoquinoline was designed and synthesized for sequentially recognizing Zn2+ and PPi. In aqueous solution, LP exhibited the ratiometric fluorescence response towards Zn2+, along with the about 4-folds enhancement of fluorescence quantum yield. Subsequently, the LP-Zn2+ complex displayed the fluorescence recovery upon adding PPi through the displacement strategy. And the LODs of LP and its Zn2+ complex for sensing Zn2+ and PPi were found to be 15 nM and 5.5 nM, respectively. Notably, the reversibility of LP for sequentially sensing Zn2+ and PPi had been employed to construct the INHIBIT logic gate. Moreover, LP and its Zn2+ complex had been successfully utilized for the detection of Zn2+ and PPi in two real water samples and cells imaging.

Turn-On Solid-State Fluorescent Determination of Zinc Ion by Quinoline-Based Covalent Organic Framework

A new quinoline-based COF (covalent organic framework), obtained by Povarov reaction, containing 2,6-diisopropylphenyl moieties as substituents over the heterocyclic ring is described for detecting Zn2+ in aqueous solution. The introduction of the mentioned bulky phenyl rings into the network favors an increase of the distance between the reticular sheets and their arrangement, obtaining a new material with an alternating AB type stacking. The new material exhibits good selectivity to detect Zn2+ by fluorescence emission in aqueous solutions up to a concentration of 1.2 × 10-4 m of the metal ion. In order to have a deeper insight into the interaction between the COF and the zinc cation, a thorough spectroscopical, microscopical, and theoretical study is also presented and discussed in this communication.

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 156 nm (λex = 350 nm, λem = 506 nm) 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 31.8 nM 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 63.2 nM 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.

A new chromone functionalized isoqunoline derived chemosensor with fluorogenic switching effect for selective detection of Zn2+ in real water samples and living cells

In this work, a selective chemosensor, (E)-N'-((4-oxo-4H-chromen-3-yl)methylene)isoquinoline-1-carbohydrazide (ENO), was rationally developed for colorimetric and fluorogenic detection of Zn²⁺ ions. It was readily synthesized from 4-oxo-4H-chromene-3-carbaldehyde and isoquinoline-1-carbohydrazide via one-step Schiff reaction. ENO exhibited excellent fluorescent response performances toward Zn²⁺ over a wide pH range in EtOH/H₂O media, including a distinguished color change from colorless to gold, a low limit of detection (LOD) value (34 nM), strong complexation ability (1.36 × 10⁵ M^-1) and rapid identification (2 min). The sensing mechanism of ENO toward Zn²⁺ was proposed on the basis of the chelation-enhanced fluorescence (CHEF) process, which was further supported by IR studies and the density functional theory (DFT) calculation. Moreover, ENO presented here demonstrated outstanding capability in monitoring trace level of Zn²⁺ ions in real water samples, living cells as well as the on-site assay kit.

Selective Detection of Mg 2+ for Sensing Applications in Drinking Water

A new series of ligands containing the 2‐(2‐hydroxy‐3‐ naphthyl)‐4‐methylbenzoxazole (HNBO) fluorophore showed selectivity for Mg²⁺ ions, without the interference of Ca²⁺. The most promising representative L3 resulted the best performing sensor for Mg²⁺ both in solution and embedded in an all‐solid‐state optode, especially towards real samples of drinkable water.

A multi-binding site hydrazone-based chemosensor for Zn(ii) and Cd(ii): a new strategy for the detection of metal ions in aqueous media based on aggregation-induced emission

A multi-binding site chemosensor, N-(3-methoxy-2-hydroxybenzylidene)-3-hydroxy-2-naphthahydrazone (H₃L), with excited-state intramolecular proton transfer (ESIPT) behaviour was prepared and characterized. It possesses no aggregation-induced emission (AIE) characteristics but can detect Cd²⁺ and Zn²⁺ ions selectively in the "off-on" mode based on the AIE of their complexes in the media of THF/HEPES and THF/H₂O, respectively, which will provide a new strategy for target detection based on AIE. The detection limits of Zn²⁺ and Cd²⁺ were 9.85 × 10^-9 M and 1.27 × 10^-7 M, respectively. The aggregates of the complexes formed in the detection system were confirmed by DLS data and SEM images. The corresponding Zn²⁺ (1) and Cd²⁺ (2) complexes were prepared to investigate the response mechanism. Powder X-ray diffraction and single crystal X-ray diffraction proved that complex 1 is the species formed in the detection system. The chemosensor coordinates with the Cd²⁺ and Zn²⁺ ions in different formation and coordination modes, leading to the emission position of the aggregates at 560 and 645 nm, respectively, based on which Cd²⁺ ions were successfully differentiated from Zn²⁺ ions. Moreover, the detection of Cd²⁺ and Zn²⁺ ions was realized qualitatively via test paper and quantitatively in water.

Adsorption mechanism of rhein-coated Fe3O4 as magnetic adsorbent based on low-field NMR

In the present study, a magnetic adsorbent, rhein-coated magnetic Fe₃O₄ nanoparticle (RMNP), for Pb²⁺ and Mg²⁺ had been developed, and adsorption mechanism was studied via low-field NMR. RMNP was characterized by TEM, FTIR, and XRD. RMNP could adsorb and remove Pb²⁺ and Mg²⁺ from water and was successfully applied to remove Pb²⁺ and Mg²⁺ from wastewater, with satisfactory recovery rates and high adsorption capacities. The calculated maximum adsorption capacity for Mg²⁺ and Pb²⁺ was approximately 69.3 and 64.9 mg g^-1 of RMNP, respectively, which was better than some results reported. Low-field NMR results showed that Pb²⁺ or Mg²⁺ enhanced the T₂ relaxation time of RMNP, which suggested that RMNP selectively coordinated with Pb²⁺ or Mg²⁺ and led to the aggregation of RMNP, furthermore removal of Pb²⁺ or Mg²⁺ from water. The standard curves for △T₂-cation concentration exhibited good line correlation. The linear ranges were from 4.2 × 10^-6 to 2.0 × 10^-4 mol L^-1 for Pb²⁺ and from 5.0 × 10^-6 mol L^-1 to 1.0 × 10^-4 mol L^-1 for Mg²⁺, respectively. The limits of detection were 1.4 × 10^-6 mol L^-1 for Pb²⁺ and 2.1 × 10^-6 mol L^-1 for Mg²⁺, respectively. In short, low-field NMR could clearly display the interaction between RMNP and Pb²⁺ or Mg²⁺, even be used to detect Pb²⁺ or Mg²⁺ in suitable condition. Besides, this method could be expanded to study the interaction between other magnetic adsorbents and analytes.

Developing a new chemosensor targeting zinc ion based on two types of quinoline platform

A chemosensor DQ (2-(2-(quinolin-2-yl)hydrazinyl)-N-(quinolin-8-yl)acetamide), based on two quinoline moieties, has been synthesized. DQ could detect zinc ion through fluorescence turn-on in aqueous media. Limit of detection was calculated as 0.07 μM, far lower than the standard of WHO for zinc ion. The practicality of DQ was demonstrated via the successful results of reusability with EDTA, easy detection on the test strip, and precise quantification in real water samples. Additionally, sensor DQ could be applied to bioimaging of zinc ion in zebrafish. Sensing process of zinc ion by DQ was studied through fluorescence and UV-Vis spectroscopy, ¹H NMR titration, and ESI-mass spectrometry.

Biocompatible alkyne arms containing Schiff base fluorescence indicator for dual detection of CdII and PbII at physiological pH and its application to live cell imaging

An alkyne arms containing salen-type Schiff base ligand L acts as a dual sensor for Cd^II and Pb^II with well-separated excitation and emission wavelengths. The ligand L has been utilized in cell imaging studies for both metal ions.

A selective “turn-on” sensor for recognizing In3+ and Zn2+ in respective systems based on imidazo[2,1-b]thiazole

An imidazo[2,1-b]thiazole-based compound (X) was designed and synthesized as an “off–on–off” sensor for the multiple recognition of In³⁺ and Zn²⁺ in different systems.

Simple Fluorescence Turn-On Chemosensor for Selective Detection of Ba2+ Ion and Its Live Cell Imaging

A phenoxazine-based fluorescence chemosensor 4PB [(4-(tert-butyl)-N-(4-((4-((5-oxo-5H-benzo[a]phenoxazin-6-yl)amino)phenyl)sulfonyl)phenyl)benzamide)] was designed and synthesized by a simple synthetic methods. The 4PB fluorescence chemosensor selectively detects Ba²⁺ in the existence of other alkaline metal ions. In addition, 4PB showed high selectivity and sensitivity for Ba²⁺ detection. The detection limit of 4PB was 0.282 μM and the binding constant was 1.0 × 10⁶ M^-1 in CH₃CN/H₂O (97.5:2.5 v/v, HEPES = 1.25 mM, pH 7.3) medium. This chemosensor functioned through the intramolecular charge transfer (ICT) mechanism, which was further confirmed by DFT studies. Live cell imaging in MCF-7 cells confirmed the cell permeability of 4PB and its capability for specific detection of Ba²⁺ in living cells.

A dual functional fluorescent sensor for the detection of Al3+ and Zn2+ in different solvents

A new fluorescent sensor, X, was designed and synthesized based on imidazo[2,1-b]thiazole and 2-hydroxy-1-naphthaldehyde, which could be used to detect Al³⁺ in methanol buffer solution and detect Zn²⁺ in ethanol buffer solution, respectively.