Anion Sensors Research Articles

A dual-electrode oxide ion sensor for molten carbonates

• A simple sensor for detecting O 2– concentration in molten carbonate was proposed. • The sensor is applicable over both wide temperature and O 2– concentration ranges. • A fast response corresponding to varying O 2– activity can be achieved within a few seconds. • The electrochemical sensor is reliable and reusable with an excellent long-term stability. • The sensor can serve as an indicator for O 2– -involved (electro)chemical reactions. The concentration of oxide ions (O 2– ) determines the physicochemical properties of molten carbonates and modulates (electro)chemical reactions. However, it still lacks an efficient and reliable method to measure O 2– concentration in molten carbonates. Herein, we design a dual-electrode sensor to monitor the O 2– content in real time. For sensing O 2– in the target molten medium, we deliberately selected a Ni/NiO redox couple to serve as an O 2– -responding internal reference membrane electrode (RE in ) assembled in an yttrium-stabilized zirconia tube, which is accessible to achieve a stable and excellent response of O 2– from the bulk melt. To measure the membrane potential of RE in that is associated with the O 2– concentration in the bulk melt, we paired a Ag/Ag 2 SO 4 external reference electrode (RE ex ), which can indicate the potential difference between RE in and RE ex by measuring the open circuit potential (OCP), therefore figuring out the O 2– concentration based on Nernst equation. Taking molten Li 2 CO 3 -Na 2 CO 3 -K 2 CO 3 for example, the homemade dual-electrode sensor is well-responsive with a reliable linear correlation coefficient of R 2 = 0.9992 even the O 2– content is as low as 1.27 × 10 −4 mol kg −1 . The proposed dual-electrode gives clues to the rational design of anion sensor for relatively high-temperature systems.

Substitution position effects of an electron-withdrawing group on the tautomer fluorescence of Coumarin–urea derivatives with an acetate anion

To improve the fluorescence properties of coumarin–urea derivatives having a phenyl urea group bound at the 7-position of the coumarin ring (7CU derivatives), the substitution position effects of the electron-withdrawing group, CF3, on the photochemical behaviors of 7CU derivatives were investigated in the absence and presence of an acetate anion (AcO−). Both o- and m-CF3-7CU were prepared besides p-CF3-7CU, all of which bear a CF3 group at different positions on a phenyl ring opposite to the coumarin ring (o-, m-, and p-isomers, respectively). These three CF3–7CU derivatives underwent excited-state intermolecular proton transfer (ESPT) in the presence of AcO− followed by emissive tautomer formation, resulting in dual fluorescence. To elucidate the fluorescence state of tautomer, we compared the spectroscopic results of CF3–7CU derivatives including the rate constants for ESPT with regard to the inductive and resonance effects. The results revealed that the emission yield of tautomer of o-CF3-7CU was an order of magnitude larger than those of both m- and p-CF3-7CU due to the effective inductive effect of a CF3 group; this observation indicates that o-CF3-7CU is a suitable anion sensor. Our findings will contribute to the development of new molecular designs for fluorescent probes with excellent visibility.

Fluoride ion sensing with an acridinium borane

With our continuing interest in the chemistry of cationic boranes, we have synthesized the tetrafluoroborate salt of 1-dimesitylboron-4-( N-methyl-9-acridinium)-phenylene, which acts as a turn-on fluoride anion sensor, visibly changing from yellow to orange upon binding fluoride. To understand this reactivity, we spectroscopically and computationally analyzed the cation and fluoroborate adduct. Ultraviolet–visible spectroscopy and time-dependent density functional theory calculations revealed the basis of the color change to be a low energy redshift in a intramolecular charge transfer band. Electrochemical studies were undertaken to further probe this system. Cyclic voltammetry indicated a reversible one-electron reduction for the cation and a cathodic shift of −0.12 V in the first reduction wave upon fluoride binding. Chemical reduction of the cation yielded the acridine borane radical, which was verified by electron paramagnetic resonance spectroscopy.

Indazole-Derived Mono-/Diruthenium and Heterotrinuclear Complexes: Switchable Binding Mode, Electronic Form, and Anion Sensing Events.

The article deals with the newer classes of mononuclear: [(acac)2RuIII(H-Iz)(Iz-)] 1, [(acac)2RuIII(H-Iz)2]ClO4 [1]ClO4/[1']ClO4, and [(bpy)2RuII(H-Iz)(Iz-)]ClO4 [2]ClO4, mixed-valent unsymmetric dinuclear: [(acac)2RuIII(μ-Iz-)2RuII(bpy)2]ClO4 [3]ClO4, and heterotrinuclear: [(acac)2RuIII(μ-Iz-)2MII(μ-Iz-)2RuIII(acac)2] (M = Co:4a, Ni:4b, Cu:4c, and Zn:4d) complexes (H-Iz = indazole, Iz- = indazolate, acac = acetylacetonate, and bpy = 2,2'-bipyridine). Structural characterization of all the aforestated complexes established their molecular identities including varying binding modes (Na and Nb donors and 1H-indazole versus 2H-indazole) of the heterocyclic H-Iz/Iz- in the complexes. Unlike [1']ClO4 containing two NH protons at the backface of H-Iz units, the corresponding [1]ClO4 was found to be unstable due to the deprotonation of its positively charged quaternary nitrogen center, and this resulted in the eventual formation of the parent complex 1. A combination of experimental and density functional theory calculations indicated the redox noninnocent feature of Iz- in the complexes along the redox chain. The absence of intervalence charge transfer transition in the near-infrared region of the (Iz-)2-bridged unsymmetric mixed-valent RuIIIRuII state in [3]ClO4 suggested negligible intramolecular electronic coupling corresponding to a class I setup (Robin and Day classification). Heterotrinuclear complexes (4a-4d) exhibited varying spin configurations due to spin-spin interactions between the terminal Ru(III) ions and the central M(II) ion. Though both [3]ClO4 and 4a-4d displayed ligand (Iz-/Iz•)-based oxidation, reductions were preferentially taken place at the bpy and metal (RuIII/RuII) centers, respectively. Unlike 1 or [2]ClO4 containing one free NH proton at the backface of H-Iz, [1']ClO4 with two H-Iz units could selectively and effectively recognize F-, OAc-, and CN- among the tested anions: F-, OAc-, CN-, Cl-, Br-, I-, SCN-, HSO4-, and Η2PΟ4- in CH3CN via intermolecular NH···anion hydrogen bonding interaction. The difference in the sensing feature between [1']ClO4 and 1/[2]ClO4 could be rationalized by their pKa values of 8.4 and 11.3/10.8, respectively.

Real scenario of metal ion sensor: is conjugated polymer helpful to detect hazardous metal ion

Abstract Metal ions from natural and anthropogenic sources cause pollution to society and the environment is major concern in the present scenario. The deposition and contamination of metal ions in soil and water affect the biogeochemical cycles. Thus, it threatens the everyday life of living and non-living organisms. Reviews on the detection of metal ions through several techniques (Analytical methods, electrochemical techniques, and sensors) and materials (Nanoparticles, carbon dots (quantum dots), polymers, chiral molecules, metal-organic framework, carbon nanotubes, etc.) are addressed separately in the present literature. This review reveals the advantages and disadvantages of the techniques and materials for metal ion sensing with crucial factors. Furthermore, it focus on the capability of conjugated polymers (CPs) as metal ion sensors able to detect/sense hazardous metal ions from environmental samples. Six different routes can synthesize this type of CPs to get specific properties and better metal ion detecting capability in vast research areas. The metal ion detection by CP is time-independent, simple, and low cost compared to other materials/techniques. This review outlines recent literature on the conjugated polymer for cation, anion, and dual ion sensors. Over the last half decades published articles on the conjugated polymer are discussed and compared.

Ultrasensitive and miniaturized ion sensors using ionically imprinted nanostructured films

The detection of ions is essential for a wide range of applications including biomedical diagnosis, and environmental monitoring among others. However, current ion sensors are based on thick sensing films (∼100 µm), requiring time-consuming preparations, and they have a limit to their sensitivity of 59 mV.Log [C]−1. Consequently, these sensors cannot be applied for high-precision applications that require high sensitivity and reduced dimensions. Furthermore, the research of anion sensors is hampered given the limited availability of molecular receptors or ionophores with acceptable performances. In this work, we overcome these limitations using a 300 nm thick sensing film based on nanoporous ion-imprinted core-shell silica/gold grafted onto a 50 nm gold film. The sensing films were highly selective towards chloride ions, compared to other anions such as nitrate, sulphate and carbonate. Moreover, this nanostructured film exhibited over 3-fold higher sensitivity (-186.4 mV.Log [C]−1) towards chloride ions compared to commercial devices. This breakthrough has led to the fabrication of the smallest and most sensitive reported anion sensor working on open circuit potentiometry, with an exceptional selectivity towards chloride ions that could be used for the measurement of chloride ions in human serum.

Fluoride-selective chemosensor based on an anion imprinted fluorescent polymer

The sensing of fluoride ion through convenient and inexpensive methods has become significant analytical goals. The state-of-the-art involves the supporting of urea/thiourea optical discrete anion sensors into a polymeric scaffold. Nevertheless, high levels of selectivity are difficult to achieve, since the colorimetric/fluorometric response is also quenched by other anions such as dihydrogenphosphate. In this work we present, for the first time, the design of a polymeric optical fluoride chemosensor by using the anion-imprinting technique. First, four polymerizable anion receptors containing a urea-type binding site and different fluorophores as signaling units were prepared. One of them (1-(4-vinylphenyl)-3-(1-naphtyl)-urea) shows the most intense fluorescence emission in solution, exhibiting high optical sensitivity only for F– and H2PO4–. The electronic and structural features behind the optical response and anion affinity were elucidated through experimental and computational tools. To enhance the optical sensitivity and selectivity, a fluoride-imprinted polymeric optical sensor was prepared starting from this soluble sensor. The fluorescent emission is 13 times higher for the polymer and it is switched off only in the presence of fluoride, while for the rest of the anions, including H2PO4–, there was almost no optical response. To the best of our knowledge, this is the first fluoride-imprinted polymeric optical sensor reported so far.

Lab-on-Paper Strip Chemical Sensor: Reversible Visible Sensor for Detection of Acids Using Naphthalenediimide Derivative

Naphthalenediimide derivatives have shown applications in the area of chemical sensors for anions due to their special optical and electrical properties. In the current work, NDI derivative having phenyl amine end group (PPD-NDI) has been synthesized and tested for sensitivity towards trifluoroacetic acid (TFA), hydrochloric acid (HCl), nitric acid (HNO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) and sulfuric acid (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) for 1-65 mM concentrations. PPD-NDI displays reversible optical and visible sensitivity for detection of acids, specially, for HCl and TFA. PPD-NDI shows charge transfer band in the range of 500-600 nm in absorption spectra along with color change in presence of acid. To understand the mechanism of sensitivity, an exclusion method has been applied by analyzing other reference NDI molecules with different end groups and linkers. PPD-NDI shows selective sensitivity for TFA present in low concentration (1 mM) and HCl at all other concentrations. Binding constants for the association between PPD-NDI and acids are obtained from the Benesi Hildebrand plot and highest value is observed in case of TFA. The sensitivity of NDI derivatives can be very helpful in detection of acids in various industrial effluents from cloth, paper, refineries and in smelting industries. We have demonstrated the reversible lab-on paper strip testing experiment for detection of HCl acid by naked eye in low and high concentrations without need of any excitation light source.

Excellent Crystallinity and Stability Covalent–Organic Frameworks with High Emission and Anions Sensing

Covalent-organic frameworks (COFs) are a new class of porous crystalline frameworks with high π-conjugation and periodical skeletons. The highly ordered π-conjugation structures in some COFs allow exciton migration and energy transfer over the frameworks, which leads to good fluorescence probing ability. In this work, two COFs (TFHPB-TAPB-COF and TFHPB-TTA-COF) are successfully condensed via the Schiff base condensation reaction. The intramolecular hydrogen bonds between imine bonds and hydroxyl groups form the excited-state intramolecular proton transfer (ESIPT) strategy. Owing to intramolecular hydrogen bonds in the skeleton, the two COFs show high crystallinity, remarkable stability, and excellent luminescence. The COFs represent a good sensitivity and selectivity to fluoride anions via fluorescence turn-off. Other halogen anions (chloride, bromide, and iodine) and acid anions (nitrate and hydrogen carbonate) remain inactive. These results imply that only fluoride anion is capable of opening the hydrogen bond interaction and hence break the ESIPT strategy. The detection limit toward fluoride anion is down to nanomoles level, ranking the best performances among fluoride anion sensors systems.

Anion-Sensing Properties of Cyclopentaphenylalanine.

Cyclic pentaphenylalanine was studied as an efficient anion sensor for halides, thiocyanate and oxoanions in acetonitrile and methanol. Stability constants of the corresponding complexes were determined by means of fluorimetric, spectrophotometric, 1H NMR, and microcalorimetric titrations. A detailed structural overview of receptor–anion complexes was obtained by classical molecular dynamics (MD) simulations. The results of 1H NMR and MD studies indicated that the bound anions were coordinated by the amide groups of cyclopeptide, as expected. Circular dichroism (CD) titrations were also carried out in acetonitrile. To the best of our knowledge, this is the first example of the detection of anion binding by cyclopeptide using CD spectroscopy. The CD spectra were calculated from the structures obtained by MD simulations and were qualitatively in agreement with the experimental data. The stoichiometry of almost all complexes was 1:1 (receptor:anion), except for dihydrogen phosphate where the binding of dihydrogen phosphate dimer was observed in acetonitrile. The affinity of the cyclopeptide receptor was correlated with the structure of anion coordination sphere, as well as with the solvation properties of the examined solvents.

Electrochemical investigation for enhancing cellular antioxidant defense system based on a superoxide anion sensor

The dynamic balance of the redox system in living organisms can be disrupted by excessive superoxide anion (O2•−), which would lead to oxidative stress and induce a variety of diseases. In this case, the antioxidant defense system plays a vital role in maintaining life and health. Thus, constructing a highly sensitive sensor for detecting O2•− and enhancing antioxidant defense systems are of great significance for reducing the risk of diseases caused by oxidative stress. In this work, a MOF-derived carbon-based nanomaterial (AgNPs-MC) was synthesized through silver-based metal organic framework. The non-enzymatic O2•− electrochemical sensor fabricated by AgNPs-MC showed excellent catalytic ability, wide linear range, and an ultra-low detection limit (12.3 pM, S/N = 3). In addition, it could be successfully used to detect O2•− released by living cells. More importantly, the synergistic effect of superoxide dismutase (SOD) and tea polyphenols (TP) to scavenge O2•− in biological systems was first studied by electrochemical method, which provides a novel strategy for improving the antioxidant defense system of living cells. Constructed sensing platform and developed antioxidant strategy have potential value for their future application in the diagnosis and treatment of diseases related oxidative stress.

Redox-Switchable Chalcogen Bonding for Anion Recognition and Sensing.

Inspired by the success of its related sigma-hole congener halogen bonding (XB), chalcogen bonding (ChB) is emerging as a powerful noncovalent interaction with a plethora of applications in supramolecular chemistry and beyond. Despite its increasing importance, the judicious modulation of ChB donor strength remains a formidable challenge. Herein, we present, for the first time, the reversible and large-scale modulation of ChB potency by electrochemical redox control. This is exemplified by both the switching-ON of anion recognition via ChB oxidative activation of a novel bis(ferrocenyltellurotriazole) anion host and switching-OFF reductive ChB deactivation of anion binding potency with a telluroviologen receptor. The direct linking of the redox-active center and ChB receptor donor sites enables strong coupling, which is reflected by up to a remarkable 3 orders of magnitude modulation of anion binding strength. This is demonstrated through large voltammetric perturbations of the respective receptor ferrocene and viologen redox couples, enabling, for the first time, ChB-mediated electrochemical anion sensing. The sensors not only display significant anion-binding-induced electrochemical responses in competitive aqueous-organic solvent systems but can compete with, or even outperform similar, highly potent XB and HB sensors. These observations serve to highlight a unique (redox) tunability of ChB and pave the way for further exploration of the reversible (redox) modulation of ChB in a wide range of applications, including anion sensors as well as molecular switches and machines.

Recent Progress on Designable Hybrids with Stimuli-Responsive Optical Properties Originating from Molecular Assembly Concerning Polyhedral Oligomeric Silsesquioxane.

In this review, we describe recent progress on stimuli-responsive hybrid materials based on polyhedral oligomeric silsesquioxane (POSS) and their applications as a chemical sensor. In particular, we explain the unique functions originating from molecular assembly concerning POSS-containing soft materials mainly from our studies. POSS has an inorganic cubic core composed of silicon-oxygen (Si-O) bonds and organic substituents at each vertex. Owing to intrinsic properties of POSS, such as high thermal stability, rigidity, and low chemical reactivity, various robust hybrid materials have been developed. From the numerous numbers of POSS hybrids, we herein focus on the environment-sensitive optical materials in which molecular assembly of POSS itself and functional units connected to POSS should be a key factor for expressing material properties. We also explain the mechanisms of chemical sensors originating from these stimuli-responsive optical properties. Stimuli-responsive excimer emission and pollutant detectors, nanoplastic sensors with the water-dispersive POSS networks, trans fatty acid sensors, turn-on luminescent sensors for aerobic condition and fluoride anion sensors are described. We also mention the mechanochromic polyurethane hybrids and the thermally-durable mechanochromic luminescent materials. The roles of the unique optical properties from soft materials composed of rigid POSS, which doesn't have significant light-absorption and emission properties in the visible region, are surveyed.

Potensi Eceng Gondok (Eichhornia Crassiper) Sebagai Kalorimetri Kation dan Anion

One of the compounds contained in water hyacinth is delhinidine 3-diglucosin. The compound is a compound that has the potential as a sensor for cations and anions because it has active groups, namely OH- and O. This study used the maceration method, then several tests were carried out, which obtained a water content of 10.24% and an ash content of 14.67%. The solvatochromic test on distilled water, methanol and acetone showed that there was a bathochromic shift and a hipsochromic shift. Meanwhile, the ionochromic qualitative test showed that the identification of cations was better than the anion test. The cation results showed that in distilled water (Yellow), water hyacinth could identify Cu2+ and Fe3+ (Green), in methanol solvent (Green) for Fe3+ metal (Yellow) while in acetone solvent (Green) it could identify Pb2+, and Fe3+ ( Yellow).

Fluorescence Sensors Based on Hydroxycarbazole for the Determination of Neurodegeneration-Related Halide Anions.

The environmental presence of anions of natural origin or anthropogenic origin is gradually increasing. As a tool to tackle this problem, carbazole derivatives are an attractive gateway to the development of luminescent chemosensors. Considering the different mechanisms proposed for anion recognition, the fluorescence properties and anion-binding response of several newly synthesised carbazole derivatives were studied. Potential anion sensors were designed so that they combined the native fluorescence of carbazole with the presence of hydrogen bonding donor groups in critical positions for anion recognition. These compounds were synthesised by a feasible and non-expensive procedure using palladium-promoted cyclodehydrogenation of suitable diarylamine under microwave irradiation. In comparison to the other carbazole derivatives studied, 1-hydroxycarbazole proved to be useful as a fluorescent sensor for anions, as it was able to sensitively recognise fluoride and chloride anions by establishing hydrogen bond interactions through the hydrogen atoms on the pyrrolic nitrogen and the hydroxy group. Solvent effects and excited-state proton transfer (ESPT) of the carbazole derivatives are described to discard the role of the anions as Brönsted bases on the observed fluorescence behaviour of the sensors. The anion–sensor interaction was confirmed by 1H-NMR. Molecular modelling was employed to propose a mode of recognition of the sensor in terms of complex stability and interatomic distances. 1-hydroxycarbazole was employed for the quantitation of fluoride and chloride anions in commercially available medicinal spring water and mouthwash samples.

A Peptide-Based Fluorescent Sensor for Anionic Phospholipids.

Anionic phospholipids are key cell signal mediators. The distribution of these lipids on the cell membrane and intracellular organelle membranes guides the recruitment of signaling proteins leading to the regulation of cellular processes. Hence, fluorescent sensors that can detect anionic phospholipids within living cells can provide a handle into revealing molecular mechanisms underlying lipid-mediated signal regulation. A major challenge in the detection of anionic phospholipids is related to the presence of these phospholipids mostly in the inner leaflet of the plasma membrane and in the membranes of intracellular organelles. Hence, cell-permeable sensors would provide an advantage by enabling the rapid detection and tracking of intracellular pools of anionic phospholipids. We have developed a peptide-based, cell-permeable, water-soluble, and ratiometric fluorescent sensor that entered cells within 15 min of incubation via the endosomal machinery and showed punctate labeling in the cytoplasm. The probe could also be introduced into living cells via lipofection, which allows bypassing of endosomal uptake, to image anionic phospholipids in the cell membrane. We validated the ability of the sensor toward detection of intracellular anionic phospholipids by colocalization studies with a fluorescently tagged lipid and a protein-based anionic phospholipid sensor. Further, the sensor could image the externalization of anionic phospholipids during programmed cell death, indicating the ability of the probe toward detection of both intra- and extracellular anionic phospholipids based on the biological context.

A novel AIE-active imidazolium macrocyclic ratiometric fluorescence sensor for pyrophosphate anion

An imidazolium bridged macrocyclophane was synthesized as a ratiometric fluorescence sensor with aggregation-induced emission (AIE) characteristic to detect pyrophosphate anion with high selectivity among various anions. In the presence of zinc ion, macrocyclophane can form aggregates through complexation with pyrophosphate anion and emit ratiometric fluorescence, resulting from an enhancement in its aggregate-state emission and a reduction in its monomer emission. This AIE-active macrocycle showed great potential as a ratiometric fluorescence receptor.

Fluoride-philic reduced graphene oxide–fluorophore anion sensors

rGO–fluorophore noncovalent conjugates efficient in the selective detection of fluoride ions in the attomolar range are presented. The high affinity of fluoride ions to rGO leads to stable graphite fluoride formation, initiating a turn-on response.

Solid-Contact Potentiometric Anion Sensing Based on Classic Silver/Silver Insoluble Salts Electrodes without Ion-Selective Membrane.

Current solid potentiometric ion sensors mostly rely on polymeric-membrane-based, solid-contact, ion-selective electrodes (SC-ISEs). However, anion sensing has been a challenge with respect to cations due to the rareness of anion ionophores. Classic metal/metal insoluble salt electrodes (such as Ag/AgCl) without an ion-selective membrane (ISM) offer an alternative. In this work, we first compared the two types of SC-ISEs of Cl− with/without the ISM. It is found that the ISM-free Ag/AgCl electrode discloses a comparable selectivity regarding organic chloride ionophores. Additionally, the electrode exhibits better comprehensive performances (stability, reproducibility, and anti-interference ability) than the ISM-based SC-ISE. In addition to Cl−, other Ag/AgX electrodes also work toward single and multi-valent anions sensing. Finally, a flexible Cl− sensor was fabricated for on-body monitoring the concentration of sweat Cl− to illustrate a proof-of-concept application in wearable anion sensors. This work re-emphasizes the ISM-free SC-ISEs for solid anion sensing.

Insights Into the Detection Selectivity of Redox and Non-redox Based Probes for the Superoxide Anion Using Coumarin and Chromone as the Fluorophores.

In this study, we evaluated the applicability of various superoxide anion sensors which were designed based on either redox or non-redox mechanisms. Firstly, both redox- and non–redox-based superoxide anion probes were designed and synthesized using either coumarin or chromone as the fluorophores, and the photophysical properties of these probes were measured. Subsequently, the sensing preference of both types of probes toward various reactive oxygen species (ROS) was evaluated. We found that non–redox-based O2 •− probes exhibited broad sensing ability toward various ROS. By contrast, redox based O2 •− probes showed a clear reactivity hierarchy which was well correlated to the oxidizing strength of the ROS. Lastly, the detection selectivity of redox-based O2 •− recognizing probes was also observed when balancing various factors, such as reactant ROS concentrations, temperature, and changing reaction transformation rates. Herein, we concluded the selectivity advantage of redox-based O2 •− probes.