Construction of MOF@COF-derived composites for ratiometric fluorescence detection of water with ultralow background

A ratiometric sensor with ultralow background is highly desired due to its low environmental influence and high sensitivity. Herein, inspired by the solubility difference of carboxylate in aqueous and organic solvents, we prepared a core-shell structure porous zirconia-covalent organic framework (COF) composite through thermal hydrolysis of UiO-66-COF precursors in organic alkali solution. The ligand 2-aminoterephthalic acids (H2BDC-NH2) of UiO-66 were transformed into 2-aminoterephthalate salts (ATA salts) that existed in zirconium-oxo clusters building units. The composites emitted only yellow emission (597 nm) from the COF in organic solvent due to the insolubility of ATA salts that induce aggregation-caused quenching (ACQ) and the protection of the COF shell. Contrarily, when water was added into mixture, the ATA salts were released into solution and its fluorescence recovered at 446 nm, while the fluorescence of COF was quenched due to the blockage of the intramolecular charge transfer (ICT) process by water. Thus, a high-sensitivity ratiometric fluorescence method is obtained with ultralow background signal and fast response (less than 1 min) for sensing water in organic solvent. We believe that the proposed ratiometric fluorescence sensor based on the zirconia-COF composite will provide the guidance for detection with wide applications.

A quinazolin-based Schiff-base chemosensor for colorimetric detection of Ni2+ and Zn2+ ions and 'turn-on' fluorometric detection of Zn2+ ion

Herein, we have reported a novel quinazolin-based Schiff base chemosensor (E)-2-benzamido-N'-(1-(pyridin-2-yl)ethylidene)benzohydrazide (L). L has been designed, synthesised and characterised by 1H-NMR, IR spectroscopy, ESI-MS spectrometry and theoretical studies. The receptor showed appreciable colorimetric λ max shift for both Ni2+ and Zn2+ ions and fluorometric "turn on" response in presence of only Zn2+ ion. The Jobs plot analysis revealed that receptor forms 2 : 1 complex with both the ions Ni2+ and Zn2+, further confirmed by ESI-MS analysis. The single crystal structure of L-Ni2+ complex (1) has also been determined. The colorimetric detection limits were calculated to 7.9 nM and 7.5 nM respectively for Ni2+ and Zn2+ in methanol-Tris-HCl buffer medium (10 mM, pH 7.2, 1 : 1 v/v). The chemosensor L can be applied for the recovery of contaminated water samples.

Active Bromoaniline-Aldehyde Conjugate Systems and Their Complexes as Versatile Sensors of Multiple Cations with Logic Formulation and Efficient DNA/HSA-Binding Efficacy: Combined Experimental and Theoretical Approach

Two fluorescence active bromoaniline-based Schiff base chemosensors, namely, (E)-4-bromo-2-(((4-bromophenyl)imino)methyl)phenol (HL1 ) and (E)-2-(((4-bromophenyl)imino)methyl)phenol (HL2 ), have been employed for the selective and notable detection of Cu2+ and Zn2+ ions, respectively, with the simultaneous formation of two new metal complexes [Cu(L1)2] (1) and [Zn(L2)2] (2). X-ray single crystal analyses indicate that complexes 1 and 2 are tetra-coordinated systems with substantial CH...π/π...π stacking interactions in the solid-state crystal structures. These two complexes are exploited for the next step detection of Al3+ and Hg2+ where complex 2 exhibits impressive results via turn-off fluorescence quenching in (DMSO/H2O) HEPES buffer medium. The sensing phenomena are optimized by UV-vis spectral analyses as well as theoretical calculations (density functional theory and time-dependent density functional theory). The combined detection phenomena of the ligand (HL2 ) and complex 2 are exclusively utilized for the first time to construct a molecular memory device, intensifying their multisensoric properties. Furthermore, the DNA- and human serum albumin (HSA)-binding efficacies of these two complexes are examined by adopting electronic and fluorometric titration methods. Complex 2 shows a higher DNA-binding ability in comparison with complex 1, whereas in the case of HSA, the reverse situation is observed. Finally, the binding modes of both the complexes with DNA and HSA have been investigated through molecular docking studies, suggesting good agreement with the experimental results.

A Cd(ii) and Zn(ii) selective naphthyl based [2]rotaxane acts as an exclusive Zn(ii) sensor upon further functionalization with pyrene

A new multi-functional [2]rotaxane, ROTX, has been synthesized via a Cu(i) catalysed azide-alkyne cycloaddition reaction between Ni(ii) templated azide terminated pseudorotaxane composed of a naphthalene based heteroditopic wheel, NaphMC, and an alkyne terminated stopper. Subsequently, ROTX has been functionalized with pyrene moieties to develop a bifluorophoric [2]rotaxane, PYROTX, having naphthalene and pyrene moieties. Detailed characterization of these two rotaxanes is performed by utilizing several techniques such as ESI-MS, (1D and 2D) NMR, UV/Vis and PL studies. Comparative metal ion sensing studies of NaphMC (a fluorophoric cyclic receptor), ROTX ([2]rotaxane with a naphthyl fluorophore) and PYROTX ([2]rotaxane having naphthyl and pyrene fluorophores) have been performed to determine the effect of dimensionality/functionalization on the metal ion selectivity. Although NaphMC fails to discriminate between metal ions, ROTX serves as a selective sensor for Zn(ii) and Cd(ii). Importantly, PYROTX shows exclusive selectivity towards Zn(ii) over various transition, alkali and alkaline earth metal ions including Cd(ii).

A Coumarin-Benzothiazole Derivative as a FRET-Based Chemosensor of Adenosine 5′-Triphosphate

A coumarin-benzothiazole ratiometric probe of ATP was designed and synthesized. The probe is based on incorporation of benzothiazole scaffold as a donor and coumarin nucleus as an acceptor in a single Förster resonance energy transfer/fluorescence resonance energy transfer (FRET) sensing platform. The sensor can detect ATP in aqueous solution with high selectivity over other nucleotide polyphosphate (NPP) anions. Binding of ATP to the sensor results in modulation of FRET efficiency between the donor and the acceptor which afforded a linear relationship between FRET signal and ATP (0.1–10 μM). A limit of detection (LOD) of 94.5 nM was quantified for FRET sensing of ATP by the probe. In addition, Job plot analysis revealed 1:1 binding interaction between the probe and ATP. The FRET probe was successfully utilized in monitoring ATP hydrolysis by apyrase in aqueous solution.

Real Time Imaging and Dynamics of Hippocampal Zn2+ under Epileptic Condition Using a Ratiometric Fluorescent Probe

Zinc, the essential trace element in human body exists either in the bound or free state, for both structural and functional roles. Insights on Zn2+ distribution and its dynamics are essential in view of the fact that Zn2+ dyshomeostasis is a risk factor for epileptic seizures, Alzheimer's disease, depression, etc. Herein, a bipyridine bridged bispyrrole (BP) probe is used for ratiometric imaging and quantification of Zn2+ in hippocampal slices. The green fluorescence emission of BP shifts towards red in the presence of Zn2+. The probe is used to detect and quantify the exogenous and endogenous Zn2+ in glioma cells and hippocampal slices. The dynamics of chelatable zinc ions during epileptic condition is studied in the hippocampal neurons, in vitro wherein the translocation of Zn2+ from presynaptic to postsynaptic neuronal bodies is imaged and ratiometrically quantified. Raman mapping technique is used to confirm the dynamics of Zn2+ under epileptic condition. Finally, the Zn2+ distribution was imaged in vivo in epileptic rats and the total Zn2+ in rat brain was quantified. The results favour the use of BP as an excellent Zn2+ imaging probe in biological system to understand the zinc associated diseases and their management.

Bipyridine bisphosphonate-based fluorescent optical sensor and optode for selective detection of Zn2+ ions and its applications

In this study, tetrabutyl 2,2′-bisbipyridine-5,5′-diylbis(methylene) diphosphonate (L) as fluorescence optical sensor was developed for selective determination of Zn²⁺.

A reductant-resistant ratiometric, colorimetric and far-red fluorescent probe for rapid and ultrasensitive detection of nitroxyl

A reductant-resistant ratiometric, colorimetric and far-red fluorescent probe for rapid and ultrasensitive detection of nitroxyl was developed.

Synthesis and optical and electrochemical properties of julolidine-structured pyrido[3,4-b]indole dye

The julolidine-structured pyrido[3,4-b]indole dye ET-1 possesses the ability to act as a calorimetric and fluorescent sensor for Brønsted and Lewis acids.

A turn-on fluorescence chemosensor based on a tripodal amine [tris(pyrrolyl-α-methyl)amine]-rhodamine conjugate for the selective detection of zinc ions

A tris(pyrrolyl-α-methyl)amine (H3tpa) and rhodamine-based conjugate (PR) served as a sensor for the selective detection of Zn²⁺and their application of imaging living cells were studied.

Fluorescent probes for the selective detection of chemical species inside mitochondria

This feature article systematically summarizes the development of fluorescent probes for the selective detection of chemical species inside mitochondria.

A simple chalcone-based ratiometric chemosensor for silver ion

Herein, we report the selective binding of Ag(+) ion by the anthracene-based chalcone receptor 1. Receptor 1 behaves as a selective and sensitive chemosensor for the recognition of Ag(+) over other heavy and transition metal ions without any interference and is capable of detecting the metal ion down to 0.15 × 10(-6) M. Receptor 1 on binding with Ag(+) ions exhibits a ratiometric fluorescence enhancement, which is due to the inhibition of photoinduced electron transfer along with the intramolecular charge transfer mechanism.

Particle-based optical sensing of intracellular ions at the example of calcium - what are the experimental pitfalls?

Colloidal particles with fluorescence read-out are commonly used as sensors for the quantitative determination of ions. Calcium, for example, is a biologically highly relevant ion in signaling, and thus knowledge of its spatio-temporal distribution inside cells would offer important experimental data. However, the use of particle-based intracellular sensors for ion detection is not straightforward. Important associated problems involve delivery and intracellular location of particle-based fluorophores, crosstalk of the fluorescence read-out with pH, and spectral overlap of the emission spectra of different fluorophores. These potential problems are outlined and discussed here with selected experimental examples. Potential solutions are discussed and form a guideline for particle-based intracellular imaging of ions.

Optical sensor: a promising strategy for environmental and biomedical monitoring of ionic species

In this review, we cover the recent developments in fluorogenic and chromogenic sensors for Cu²⁺, Fe²⁺/Fe³⁺, Zn²⁺and Hg²⁺.

Donor–linker–acceptor (D–π–A) diazine chromophores with extended π-conjugated cores: synthesis, photophysical and second order nonlinear optical properties

The synthesis, photophysical properties and second order non-linear optical response of a series of push–pull pyrimidine and quinoxaline chromophores with extended π-conjugated cores are reported.

A highly selective fluorescent chemosensor based on a quinoline derivative for zinc ions in pure water

A water-soluble fluorescent sensor with a low detection limit could be used to detect and quantify Zn²⁺in water samples.

Synthesis, optical, electrochemical and photovoltaic properties of a D–π–A fluorescent dye with triazine ring as electron-withdrawing anchoring group for dye-sensitized solar cells

D–π–A fluorescent dye OUJ-1 with 1,3,5-triazine ring as electron-withdrawing anchoring group has been newly developed and its optical and electrochemical properties, and photovoltaic performance in a dye-sensitized solar cell were investigated.

Design of ratiometric emission probe with visible light excitation for determination of Ca2+ in living cells

An organic salt as a fluorescent probe based on intramolecular charge transfer for Ca(2+) determination is developed. Ca(2+) can be detected by ratiometric emission at 490 and 594 nm with an excitation wavelength of 405 nm. This probe is highly selective for Ca(2+) over other divalent metal cations and displays a large Stokes shift of 189 nm that can avoid interference of the excitation light beam and autofluorescence of biological samples. The dissociation constant for Ca(2+) is 2.25 ± 0.47 μM and pertinent to Ca(2+) detection in cellular resting and dynamic states. The probe demonstrates its application in monitoring Ca(2+) in living cells under confocal microscopic imaging.