Anion Sensors Research Articles

Increasing the selectivity of optical anion sensors with cationic extracting agents

ABSTRACT Anions play an important role in our life, from storing our genetic code on the polyanion DNA, to being the active ingredient in agricultural fertilisers and other industrial processes. Consequently, chemists have been designing systems that can sense anionic species through a variety of methods, such as unimolecular chromophores or sensor arrays. Nonetheless, most existing sensing approaches still have some drawbacks, particularly related to obtaining adequate selectivity and achieving sensing of anions in aqueous environments. In this manuscript, we report a liquid–liquid extraction (LLE)-based sensing approach that allows the conversion of non-selective optical anion sensors that only work in organic media, into selective sensing systems that allow detection of anions in water. We tested this approach on deprotonation-based anion sensors (alizarin, naphthol AS, 4-nitrophenol, BI-Lawsone, and chromophore 1) and hydrogen bonding-based anion sensors (1,2-diaminoanthraquinone and 4-nitro-1,2-phenylenediamine). In general, the deprotonation-based sensors could be converted from a non-selective sensor for basic anions (NCO¯, H2PO4¯, AcO¯ and F¯) to a selective sensing system for NCO¯ with the aid of carefully chosen tetraalkylammonium salts as extracting agents. On the other hand, the hydrogen-bonding based sensors could be converted to a selective sensing system for the hydrophobic anion ClO4¯ using similar tetraalkylammonium salts.

ChemFET Anion Sensor Based on MOF Nanoparticles.

Nanoparticles of metal-organic frameworks (nanoMOFs) possess the unusual combination of both internal and external surfaces. While internal surfaces have been the focus of fundamental and applications-based MOF studies, the chemistry of the external surfaces remains scarcely understood. Herein we report that specific ion interactions with nanoparticles of Cu(1,2,3-triazolate)2 (Cu(TA)2) resemble the Hofmeister behavior of proteins and the supramolecular chemistry of synthetic macromolecules. Inspired by these anion-selective interactions, we tested the performance of Cu(TA)2 nanoparticles as chemical field effect transistor (ChemFET) anion sensors. Rather than size-based selectivity, the detection limits of the devices exhibit a Hofmeister trend, with the greatest sensitivity towards anions perchlorate, iodide, and nitrate. These results highlight the importance of the pore-based supramolecular interactions, rather than localized donor-acceptor pairs, in designing MOF-based technologies.

Strategic Design of Anion-Responsive Triarylboranes Exhibiting Colorimetric and Fluorometric Red-Shift for Sensing and Optoelectronic Applications.

Triarylboranes (TABs) have been employed as colorimetric and/or fluorometric anion sensors. The majority of TAB-based anion sensors exhibit blue-shift modes of absorption and photoluminescence (PL) or turn off of PL, attributed to the intrinsic electronic polarity of the trivalent boron unit in their molecular designs. In this Concept article, we introduce a novel approach to modulating the photophysical properties of TABs toward a red-shift mode by balancing the dual, opposing roles of the amine-bridged TAB (phenazaborine). This molecular design strategy enables significant changes in color and emission response to anions, shifting to the lower energy regime in solution. Additionally, this approach is applicable to the solid-state modulation of PL in films and organic light-emitting diodes (OLEDs).

Dual-Hydrogen Bond Donor-Functionalized Carbon Nanotube Fibers: Enhancing Anion-Sensing Performance Through Functionalization Approaches.

In this study, chemiresistive anion sensors are developed using carbon nanotube fibers (CNTFs) functionalized with squaramide-based dual-hydrogen bond donors (SQ1 and SQ2) and systematically compared the sensing properties attained by two different functionalization methods. Model structures of the selectors are synthesized based on a squaramide motif incorporating an electron-withdrawing group. Anion-binding studies of SQ1 and SQ2 are conducted using UV-vis titrations to elucidate the anion-binding properties of the selectors. These studies revealed that the chemical interaction with acetate (AcO-) induced the deprotonation of both SQ1 and SQ2. Selectors are functionalized onto the CNTFs using either covalent or non-covalent functionalization. For covalent functionalization, SQ1 is chemically formed on the surface of the CNTFs, whereas SQ2 is non-covalently functionalized to the surface of the CNTFs assisted by poly(4-vinylpyridine). The results showed that non-covalently functionalized CNTFs exhibited a 3.6-fold higher sensor response toward 33.33mm AcO- than covalently functionalized CNTFs. The selector library is expanded using diverse selectors, such as TU- and CA-based selectors, which are non-covalently functionalized on CNTFs and presented selective AcO--sensing properties. To demonstrate on-site and real-time anion detection, anion sensors are integrated into a sensor module that transferred the sensor resistance to a smartphone via wireless communication.

Advances in Anion Sensing Using Dipyrromethane‐Based Compounds

AbstractAnion sensing plays a crucial role in areas ranging from medical diagnostics to environmental monitoring. Dipyrromethane‐based compounds offer a versatile platform for developing colorimetric and fluorescent chemosensors, owing to their structural tunability and favorable optical properties. This review provides a concise overview of current advancements in anion sensing using dipyrromethane molecular framework. We examined the diverse strategies employed in designing dipyrromethane‐based anion sensors. Emphasis is placed on the structure‐function relationships that dictate anion affinity and selectivity. Key sensing mechanisms, including visual detection, UV‐vis studies, NMR studies, and fluorescence modulation, are explored. Finally, the synthetic routes for the synthesis of chemosensors are mentioned in detail. Given the efficiency and flexibility of dipyrromethane‐based sensor, we believe that major developments are to be expected in the field of both sensor and analytical chemistry.

Stochastic Sensing of Chloride Anions Using an α-Hemolysin Pore with a semiaza-Bambusuril Adapter.

Pores containing molecular adapters provide internal selective binding sites, thereby allowing the stochastic sensing of analytes. Herein, we demonstrate that semiaza-bambusuril (BU) acts as a non-covalent molecular adapter when lodged within the lumen of the wild-type α-hemolysin (WT-αHL) protein pore. Because the bambusurils are recognized as anion receptors, the anion binding site within the adapter-nanopore complex allows the detection of chloride anions, thus converting a non-selective pore into an anion sensor.

Investigation of the Sensing Properties of Lanthanoid Metal-Organic Frameworks (Ln-MOFs) with Terephthalic Acid.

The solvothermal synthesis of LnCl3.nH2O with terephthalic acid (benzene-1,4-dicarboxylic acid, H2BDC) produced metal-organic frameworks (LnBDC), [Ln2(BDC)3(H2O)4]∞, where Ln = Sm, Eu, Tb, and Dy. The materials obtained were characterized by a number of physico-chemical techniques. The influence of the ionic radius of the lanthanides on the microstructural characteristics of the Ln-MOFs was evaluated by performing Rietveld refinement. The MOFs obtained were tested as fluorescent sensors for numerous cations and anions in water. The highly luminescent EuBDC and TbBDC demonstrated multi-responsive luminescence sensing functions to detect Ag(I), Fe(III), Cr(III), and Cr(VI), which are essential for their environmental applications. By applying the non-linear Stern-Volmer equation, the fluorescent quenching mechanism was determined. The stability of the obtained materials in water in a wide pH range (acidity pH = 4 and alkalinity pH = 9 solutions) was confirmed.

Stochastic Sensing of Chloride Anions Using an α‐Hemolysin Pore with a semiaza‐Bambusuril Adapter

AbstractPores containing molecular adapters provide internal selective binding sites, thereby allowing the stochastic sensing of analytes. Herein, we demonstrate that semiaza‐bambusuril (BU) acts as a non‐covalent molecular adapter when lodged within the lumen of the wild‐type α‐hemolysin (WT‐αHL) protein pore. Because the bambusurils are recognized as anion receptors, the anion binding site within the adapter‐nanopore complex allows the detection of chloride anions, thus converting a non‐selective pore into an anion sensor.

Fluorescent sensors for detecting anions

Fluorescent sensors for detecting anions Nicola Edwards, Associate Professor of Chemistry at the University of St. Joseph, is conducting research on the development of fluorescent sensors for anion detection. Fluorescent (chemo)sensors are molecules that register changes in their “glow” (fluorescence ) when bound to an analyte (the substance of interest that is being studied), thus reporting the presence of that analyte. These changes can be detected with the naked eye. and/or instrumentation. Therefore, the presence of this invisible substance can now be detected. Fluorescent sensors are generally more sensitive and have lower limits of detection for a particular analyte compared to colorimetric sensors. Anions—chemical entities with an overall negative charge—are found everywhere and are involved in numerous chemical, biological, and industrial processes. As an example, cavity-fighting kinds of toothpaste and gels contain anion and fluoride. Additionally, chemical compounds containing anions, nitrate and phosphate are used in fertilizers. In this piece, Dr. Nicola Edwards discusses her ongoing work on developing fluorescent sensors for anions.

A Zn(II) Coordination Polymer for Fluorescent Turn-Off Selective Sensing of Heavy Metal Cation and Toxic Inorganic Anions.

A novel coordination polymer [Zn(atyha)2]n (1) (Hatyha = 2-(2-aminothiazole-4-yl)-2- hydroxyiminoacetic acid) was constructed by hydrothermal reaction of Zn2+ with Hatyha ligand. CP 1 exhibits a 2D (4,4)-connected topological framework with Schläfli symbol of {44·62}, where atyha- anions serve as tridentate ligands, bridging with Zn2+ through carboxylate, thiazole and oxime groups. CP 1 displays a strong ligand-based photoluminescence at 390 nm in the solid state, and remains significantly structurally stable in water. Interestingly, it can be utilized as a fluorescent probe for selective and sensitive sensing of Fe3+, Cr2O72- and MnO4- through the fluorescent turn-off effect with limit of detection (LOD) of 3.66 × 10-6, 2.38 × 10-5 and 2.94 × 10-6 M, respectively. Moreover, the efficient recyclability for detection of Fe3+ and Cr2O72- is better than that for MnO4-. The mechanisms of fluorescent quenching involve reversible overlap of UV-Vis absorption bands of the analytes (Fe3+, Cr2O72- and MnO4-) with fluorescence excitation and emission bands for CP 1, respectively.

Turn-on Coumarin Precursor: From Hydrazine Sensor to Covalent Inhibition and Fluorescence Detection of Rabbit Muscle Aldolase.

Hydrazine, a highly toxic compound, demands sensitive and selective detection methods. Building upon our previous studies with pre-coumarin OFF-ON sensors for fluoride anions, we extended our strategy to hydrazine sensing by adapting phenol protecting groups (propionate, levulinate, and γ-bromobutanoate) to our pre-coumarin scaffold. These probes reacted with hydrazine, yielding a fluorescent signal with low micromolar limits of detection. Mechanistic studies revealed that hydrazine deprotection may be outperformed by a retro-Knoevenagel reaction, where hydrazine acts as a nucleophile and a base yielding a fluorescent diimide compound (6,6'-((1E,1'E)-hydrazine-1,2diylidenebis(methaneylylidene))bis(3(diethylamino)phenol, 7). Additionally, our pre-coumarins unexpectedly reacted with primary amines, generating a fluorescent signal corresponding to phenol deprotection followed by cyclization and coumarin formation. The potential of compound 3 as a theranostic Turn-On coumarin precursor was also explored. We propose that its reaction with ALDOA produced a γ-lactam, blocking the catalytic nucleophilic amine in the enzyme's binding site. The cleavage of the ester group in compound 3 induced the formation of fluorescent coumarin 4. This fluorescent signal was proportional to ALDOA concentration, demonstrating the potential of compound 3 for future theranostic studies in vivo.

A Simple Fluorescence Sensor Based on Merocyanine 540-MnO2 System to Detect Hypochlorite

Merocyanine 540 (MC540)- Manganese oxide (MnO2) system-based fluorescence sensor is reported as an anion sensor in aqueous solution. MnO2 was synthesized in the presence of Potassium permanganate (KMnO4) and Cetyltrimethylammonium bromide (CTAB) using 3-(N-morpholino) propane sulfonic acid (MOPS) buffer. The formation of MnO2 was first confirmed by a color change and characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Ultraviolet–Visible (UV–Vis). absorption spectroscopy techniques. Next, the interaction of MC540 with MnO2 in aqueous solution was investigated at various conditions by UV–Vis. absorption and fluorescence spectroscopy. The sensing ability of the MC540-MnO2 was tested to detect hypochlorite (ClO-) ion as a “Turn-off” fluorescent sensor. The MC540-MnO2 revealed to be high selectivity and sensitivity to detect hypochlorite (ClO-) ion without being affected by the other thirteen anions. The detection limits for ClO- were evaluated in two different concentration ranges and calculated to be 0.14 μM at 0.33-4.46 μM and 0.38 μM at 5.06-14.30 μM, respectively.

A Novel Bisquaternary Ammonium Compound as an Anion Sensor-ESI-MS and Fluorescence Study.

Electrospray ionization mass spectrometry (ESI-MS) analysis is frequently associated with noncovalent adduct formation, both in positive and negative modes. Anion binding and sensing by mass spectrometry, notably more challenging compared to cation binding, will have major research potential with the development of appropriate sensors. Here, we demonstrated identification of stable bisquaternary dication adducts with trifluoroacetate (TFA-), Cl- and HSO4- in positive-mode ESI-MS analysis. The observed adducts were stable in MS/MS mode, leading to the formation of characteristic fragment ions containing a covalently bound anion, which requires bond reorganization. This phenomenon was confirmed by computational methods. Furthermore, given that anion detection and anion sensor chemistry have gained significant prominence in chemistry, we conducted an analysis of the fluorescent properties of bisquaternary ammonium compound as a potential anion sensor.

Fluorescent 5H‐Pyrano[3,2‐c]chromenes: Synthesis, Photophysical Properties and Sensing of Nucleophilic Anions

AbstractWe report the development of a convenient organocatalytic method for the synthesis of 5H‐pyrano[3,2‐c]chromenes from chromone‐containing acrylates and ethyl cyanoacetate. The synthesis is characterized by simple conditions (ethanol, basic catalysis) and good yields (up to 90 %). The synthesized pyrano[3,2‐c]chromenes are a promising new class of fluorescent compounds. They have intense fluorescence in the yellow‐green region of the spectrum (495–554 nm) with high quantum yields (up to 72 %) and exhibit large Stokes shifts (3514–5856 cm−1). We have demonstrated the possible application of the obtained pyrano[3,2‐c]chromenes as selective “turn‐off” sensors for nucleophilic anions, such as cyanide, sulfide and sulfite.

Anion Sensing through Redox‐Modulated Fluorescent Halogen Bonding and Hydrogen Bonding Hosts**

AbstractAnion sensing via either optical or electrochemical readouts has separately received enormous attention, however, a judicious combination of the advantages of both modalities remains unexplored. Toward this goal, we herein disclose a series of novel, redox‐active, fluorescent, halogen bonding (XB) and hydrogen bonding (HB) BODIPY‐based anion sensors, wherein the introduction of a ferrocene motif induces remarkable changes in the fluorescence response. Extensive fluorescence anion titration, lifetime and electrochemical studies reveal anion binding‐induced emission modulation through intramolecular photoinduced electron transfer (PET), the magnitude of which is dependent on the nature of both the XB/HB donor and anion. Impressively, the XB sensor outperformed its HB congener in terms of anion binding strength and fluorescence switching magnitude, displaying significant fluorescence turn‐OFF upon anion binding. In contrast, redox‐inactive control receptors display a turn‐ON response, highlighting the pronounced impact of the introduction of the redox‐active ferrocene on the optical sensing performance. Additionally, the redox‐active ferrocene motif also serves as an electrochemical reporter group, enabling voltammetric anion sensing in competitive solvents. The combined advantages of both sensing modalities were further exploited in a novel, proof‐of‐principle, fluorescence spectroelectrochemical anion sensing approach, enabling simultaneous and sensitive read out of optical and electrochemical responses in multiple oxidation states and at very low receptor concentration.

Anion Sensing through Redox-Modulated Fluorescent Halogen Bonding and Hydrogen Bonding Hosts.

Anion sensing via either optical or electrochemical readouts has separately received enormous attention, however, a judicious combination of the advantages of both modalities remains unexplored. Toward this goal, we herein disclose a series of novel, redox-active, fluorescent, halogen bonding (XB) and hydrogen bonding (HB) BODIPY-based anion sensors, wherein the introduction of a ferrocene motif induces remarkable changes in the fluorescence response. Extensive fluorescence anion titration, lifetime and electrochemical studies reveal anion binding-induced emission modulation through intramolecular photoinduced electron transfer (PET), the magnitude of which is dependent on the nature of both the XB/HB donor and anion. Impressively, the XB sensor outperformed its HB congener in terms of anion binding strength and fluorescence switching magnitude, displaying significant fluorescence turn-OFF upon anion binding. In contrast, redox-inactive control receptors display a turn-ON response, highlighting the pronounced impact of the introduction of the redox-active ferrocene on the optical sensing performance. Additionally, the redox-active ferrocene motif also serves as an electrochemical reporter group, enabling voltammetric anion sensing in competitive solvents. The combined advantages of both sensing modalities were further exploited in a novel, proof-of-principle, fluorescence spectroelectrochemical anion sensing approach, enabling simultaneous and sensitive read out of optical and electrochemical responses in multiple oxidation states and at very low receptor concentration.

Synthesis and characterization of La QDs: sensors for anions and H2O2

Synthesis and characterization of La QDs: sensors for anions and H₂O₂

Halogen bonding aza-BODIPYs for anion sensing and anion binding-modulated singlet oxygen generation.

Two novel aza-BODIPY based anion sensors, decorated with halogen bonding recognition sites, are capable of detecting halide anions at biologically-relevant near-IR wavelengths. With potential application for improving the selectivity of photodynamic therapy agents, unprecedented supramolecular host-guest anion binding-modulated singlet oxygen generation is demonstrated.

A Soluble Porous Coordination Polymer for Fluorescence Sensing of Explosives and Toxic Anions under Homogeneous Environment.

In the past decades, porous coordination polymers (PCPs) based fluorescent (FL) sensors have received intense attention due to their promising applications. In this work, a soluble Zn-PCP is presented as a sensitive probe towards explosive molecules, chromate, and dichromate ions. In former reports, PCP sensors were usually ground into fine powders and then dispersed in solvents to form FL emulsion for sensing applications. However, their insoluble characters would cause the sensing accuracy which is prone to interference from environmental effects. While in this work, the as-made PCP could be directly soluble in organic solvents to form a clear solution with bright blue emission, representing the first soluble PCP based fluorescence sensor to probe explosive molecules under a homogeneous environment. Moreover, the FL PCP solution also shows sensitive detection behaviors towards the toxic anions of CrO42- and Cr2O72-, which exhibit a good linear relationship between the fluorescence intensity of Zn-PCP and the concentrations of both analytes. This work provides a reference for designing task-specific PCP sensors utilized under a homogeneous environment.

Dual-mode fluorescence and colorimetric sensing of sulfide anion in natural water based on near-infrared Ag2S quantum dots and MnO2 nanosheets complex

Near infrared (NIR) emission Ag2S quantum dots (QDs) are of great value for biochemical sensing with strong anti-interference and low toxicity. Herein, NIR fluorescence Ag2S QDs were synthesized successfully. Combined with the excellent oxidase-like characteristics of manganese dioxide (MnO2) nanosheets, a fluorescence and colorimetric dual-mode sensor for sulfide anion was developed. MnO2 nanosheets could effectively catalyze the oxidation of TMB to produce blue TMB oxide (ox TMB), at the same time, the fluorescence of Ag2S QDs could be effectively quenched by fluorescence internal filtration effect (IFE) and dynamic quenching effect. The enzyme-like activity was weakened and the NIR fluorescence of Ag2S QDs was restored when sulfide anion (S2−) was added, due to the reduction of MnO2 to Mn2+.The linear ranges for fluorescence and colorimetric analysis of S2− were 2–250 μM and 0.3–50 μM, with detection limits of 0.6 and 0.215 μM, correspondingly. The dual-mode sensor had a wider detection range, higher sensitivity and shorter reaction time, which could be used for highly selective detection of S2− in different concentration ranges. In addition, it had been successfully applied to the determination of sulfide in water samples with satisfactory accuracy and sensitivity.