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Polymeric membrane ion-selective electrodes (ISEs) have been widely used in environmental monitoring. However, in complicated marine environments, marine biofouling usually becomes a sticky problem for these electrodes. Herein, for the first time, a novel maintenance-free antifouling potentiometric marine sensor based on a self-polishing coating (SPC) is proposed. The SPC is synthesized by using the seeded emulsion polymerization method based on the triisopropylsilyl methacrylate monomer as the regulator of the self-renewal rate. This coating can be simply modified onto the electrode surface by drop-casting. The silyl acrylate side groups of the obtained SPC on the sensor surface can be hydrolyzed in the marine alkaline medium. The shear movement of seawater driven by sea waves, wind, gravity, or vibration removes the leftover (fouled) brittle polymer backbone and thus the fouling marine microorganisms. As a proof-of-concept experiment, a polymeric membrane Ca2+-ISE is chosen as a model. Compared to the unmodified electrode, the SPC-coated Ca2+-ISE exhibits remarkable improved antifouling properties in terms of superior anti-adhesive abilities towards marine microorganisms, such as bacterial cells and algae and excellent long-term stability even in the presence of high levels of marine microorganisms. Since no additional manual maintenance is required for maintaining the antifouling abilities of the sensor, the proposed self-polishing sensor may lay an important foundation for construction of unattended long-term potentiometric monitoring systems in real marine environments. [ABSTRACT FROM AUTHOR]

With the increasing concerns of human health and the ecological environment, tobacco stalks from the cigarette industry have been recognized as hazardous wastes requiring cautious treatment. However, there is still a lack of a simple and efficient route for full utilization of tobacco stalks. Herein, we attempted to convert tobacco stalk waste to value-added carbohydrates, bio-oil, and biochar through sequential hydrothermal and pyrolysis treatments. The results showed a high carbohydrate yield under the optimized condition using a microwave reaction system. The subsequent pyrolysis of residual solids at high temperatures could produce unexpected high-level aromatic chemicals including phenols and even benzenes—difficult to form without the facilitation of catalysts or salts. The obtained by-product biochar showed rapid absorption of tetracycline in 5 min and gradual introparticle diffusion from 30 to 240 min. The isotherm result had the characteristics of the Langmuir model, displaying homogeneous active sites on the biochar surface. Probably due to the hydrothermal pretreatment before pyrolysis, the obtained biochar exhibited a high adsorption capacity toward tetracycline without introducing the activation chemicals. These results illustrate that the proposed strategy may pave the way for dealing with tobacco wastes in the agricultural field. [ABSTRACT FROM AUTHOR]

Carrier-based polymeric membrane potentiometric sensors are an ideal tool for detecting ionic species. However, in the fabrication of these sensors, the screening of carriers still relies on empirical trial- and error-based optimization, which requires tedious and time-consuming experimental verification. In this work, computer-aided screening of carriers is applied in the preparation of polymeric membrane potentiometric sensors. Molecular docking is used to study the host–guest interactions between receptors and targets. Binding energies are employed as the standard to screen the appropriate carrier. As a proof-of-concept experiment, the antibiotic ciprofloxacin is selected as the target model. A series of supramolecular macrocyclic receptors including cyclodextrins, cucurbiturils and calixarenes are chosen as potential receptors. The proposed sensor based on the receptor calix[4]arene screened by molecular docking shows a lower detection limit of 0.5 μmol L−1 for ciprofloxacin. It can be expected that the proposed computer-aided screening technique of carriers can provide a simple but highly efficient method for the fabrication of carrier-based electrochemical and optical sensors. [ABSTRACT FROM AUTHOR]

In this work, we describe a novel method to improve the detection limits of the non-classical polymeric membrane ion-selective electrodes (ISEs) which are conditioned with highly discriminated ions instead of primary ions. It is based on a thin-layer ISE membrane with a thickness of 5 μm, which is coated on ordered mesoporous carbon used as solid contact. The diffusion of the primary ion from the surface of the sensing membrane to the bulk of the membrane could be avoided by the proposed thin membrane configuration. Since the detection sensitivity of the non-classical ISEs depends on the accumulation of the primary ion in the interfacial layer of the sensing membrane, a lower detection limit can be obtained. By using the copper ion as a model, the present potentiometric sensor shows a significantly improved detection sensitivity compared to the conventional ISE with a membrane thickness of ca. 200 μm. Low detection limits of 0.29 and 0.53 nM can be obtained in 0.01 and 0.5 M NaCl, respectively. In addition, the proposed sensor exhibits an excellent reversibility by using a neutral proton-selective ionophore incorporated in the thin membrane. For the first time, a thin membrane configuration based on non-equilibrium mechanism is used to improve the detection limit of the non-classical ISEs. Image 1 • A novel thin polymeric membrane potentiometric sensor is developed. • The thin membrane configuration is used to improve the detection limit of the non-classical potentiometric sensor. • The proposed sensor shows a significantly improved detection sensitivity compared to the conventional ISEs. • The thin membrane-based concept can be extended to improve sensing performance of other polymeric membrane ISEs. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Potentiometric microelectrodes are regarded as promising probes for ion sensing when only limited sample volumes are available. In this work, an all-solid-state ion-selective microelectrode (ISμE) has been developed by coating ionophore-based ion-selective membrane on a poly(3,4-ethylenedioxythiophene)-poly(sodium 4-styrenesulfonate) modified gold wire with a diameter of 14 μm for detection of copper. Under the optimized conditions, the proposed all-solid-state Cu2+-ISμE shows a Nernst response toward Cu2+ in 0.5 M NaCl in the range from 2.5 × 10−7 to 2.5 × 10−4 M with a detection limit of 4.0 × 10−8 M. Additionally, the Cu2+-ISμE has been used for monitoring the vertical distribution profile of Cu2+ in coastal sediment pore water with a small volume (e.g., 300 μL). The results agree well with those obtained by anodic stripping voltammetry, which indicates that the proposed potentiometric technique based on the all-solid-state ISμE is promising for detection of Cu2+ in coastal sediment pore water. The method for the preparation of the ISμE can be extended to detect other heavy metal ions in sediments by using different ion-selective membranes. [ABSTRACT FROM AUTHOR]

Quinclorac, a widely used herbicide in agriculture, has been recognized as an emerging environmental pollutant owing to its long persistence and potential risk to humans. However, no related information is available on the degradation of quinclorac by employing oxidants. Herein, the reactivity of quinclorac with permanganate was systematically investigated in water by combining experimental and computational approaches. The reaction followed overall second-order kinetics pointing to a bimolecular rate-limiting step. The second-order rate constant was found to be 3.47 × 10−3 M−1 s−1 at 25 °C, which was independent of pH over the range from 5 to 9 and was dependent on temperature over the range from 19 to 35 °C. The initial product was identified by UPLC-Q-TOF-MS to be mono-hydroxylated quinclorac, which was more susceptible to further oxidation. The result could be supported by the complete simulation of the reaction process in DFT calculations, indicating the [3 + 2] cycloaddition oxidation of the benzene ring in the rate-limiting step. The plausible mechanism was then proposed, accompanied by the analysis of the HOMO indicating the hydroxylation position and of the ESP suggesting a more electron-rich moiety. Considering the high effectiveness and low toxicity, permanganate oxidation was considered to be a very promising technique for removing quinclorac from aquatic environments. [ABSTRACT FROM AUTHOR]

Using sensors to quantify clinically relevant biological species has emerged as a fascinating research field due to their potential to revolutionize clinical diagnosis and therapeutic monitoring. Taking advantage of the wide utility in clinical analysis and low cost of potentiometric ion sensors, we demonstrate a method to use such ion sensors to quantify bioanalytes without chemical labels. This is achieved by combination of chronopotentiometry with a mussel-inspired surface imprinting technique. The biomimetic sensing method is based on a blocking mechanism by which the recognition reaction between the surface imprinted polymer and a bioanalyte can block the current-induced ion transfer of an indicator ion, thus causing a potential change. The present method offers high sensitivity and excellent selectivity for detection of biological analytes. As models, trypsin and yeast cells can be measured at levels down to 0.03 U mL−1 and 50 CFU mL−1, respectively. [ABSTRACT FROM AUTHOR]

Potentiometric sensors have been exploited for the determination of Hg 2+ ions. However, applications of such sensors are limited to mercury detection in the absence of a Cl − -rich background since Hg 2+ can readily form coordination complexes with Cl − . This paper describes a potentiometric sensor for the determination of anionic mercury species using tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide) as anion-selective ionophore and tridodecylmethylammonium chloride as ion exchanger. An asymmetric membrane rotating ion-selective electrode configuration is used to improve the detection sensitivity. By using HgCl 3 − as a model of anionic mercury species, the proposed method allows potentiometric detection of mercury down to nanomolar levels in samples containing 0.05 M NaCl background electrolyte. The practical application of the proposed sensor has been performed for the determination of total mercury concentrations in diluted seawater samples. [ABSTRACT FROM AUTHOR]

Highlights: [•] We report a novel potentiometric sensor based on molecularly imprinted nanoparticles. [•] Imprinted nanoparticles are used for the polymeric membrane ISE. [•] An asymmetric membrane rotating ISE is applied to improve the detection sensitivity. [•] The new method offers a low detection limit of 1.9×10−9 molL−1 for triclosan. [ABSTRACT FROM AUTHOR]

Ion-selective electrode (ISE) based potentiometric gas sensors have shown to be promising analytical tools for detection of chemical vapors. However, such sensors are only capable of detecting those vapors which can be converted into ionic species in solution. This paper describes for the first time a polymer membrane ISE based potentiometric sensing system for sensitive and selective determination of neutral vapors in the gas phase. A molecularly imprinted polymer (MIP) is incorporated into the ISE membrane and used as the receptor for selective adsorption of the analyte vapor from the gas phase into the sensing membrane phase. An indicator ion with a structure similar to that of the vapor molecule is employed to indicate the change in the MIP binding sites in the membrane induced by the molecular recognition of the vapor. The toluene vapor is used as a model and benzoic acid is chosen as its indicator. Coupled to an apparatus manifold for preparation of vapor samples, the proposed ISE can be utilized to determine volatile toluene in the gas phase and allows potentiometric detection down to parts per million levels. This work demonstrates the possibility of developing a general sensing principle for detection of neutral vapors using ISEs. [ABSTRACT FROM AUTHOR]

Polymeric membrane potentiometric sensors based on molecularly imprinted polymers (MIPs) as the receptors have been successfully developed for detection of organic and biological species. However, it should be noted that all of the polymeric membrane matrices of these sensors developed so far are the plasticized poly(vinyl chloride) (PVC) membranes, which are usually suffered from undesired plasticizer leaching. Hence, for the first time, we describe a novel plasticizer-free MIP-based potentiometric sensor. A new copolymer, methyl methacrylate and 2-ethylhexyl acrylate (MMA-2-EHA), is synthesized and used as the sensing membrane matrix. By using neutral bisphenol A (BPA) as a model, the proposed plasticizer-free MIP sensor shows an excellent sensitivity and a good selectivity with a detection limit of 32 nM. Additionally, the proposed MMA-2-EHA-based MIP membrane exhibits lower cytotoxicity, higher hydrophobicity and better MIP dispersion ability compared to the classical plasticized PVC-based MIP sensing membrane. We believed that the new copolymer membrane-based MIP sensor can provide an appealing substitute for the traditional PVC membrane sensor in the development of polymeric membrane-based electrochemical and optical MIP sensors. For the first time, a novel plasticizer-free MIP-based potentiometric sensor is described. Image 1 • A novel plasticizer-free MIP-based potentiometric sensor is developed. • A new copolymer, MMA-2-EHA, is synthesized and used as the sensing membrane matrix. • The proposed MIP sensor shows an excellent sensitivity and a good selectivity. • The proposed sensor exhibits obvious advantages in cytotoxicity and hydrophobicity. • The copolymer membrane-based strategy is generally applicable for chemical sensors. [ABSTRACT FROM AUTHOR]

The PI3K/AKT signaling pathway is commonly exploited to regulate viral replication and affect the fate of infected cells. In the present study, a PI3K-specific inhibitor (LY294002) was employed to pretreat crayfish to evaluate the effects of PI3K/AKT signaling pathway in WSSV replication. The results showed that the WSSV copy numbers in crayfish pretreated with LY294002 were significantly lower than those in Tris-HCl pretreatment crayfish on the sixth and tenth day after WSSV infection. In semigranular cells, the apoptosis rates were up-regulated on the third day post-WSSV infection, and a significantly lower proportion of apoptosis cells were observed in LY294002-pretreatment group. The expression level of Bax, Bax inhibitor-1 and lectin mRNA in haemocytes of crayfish were increased after WSSV infection. After the secondary stimulation with Tris-HCl, the Bax expression level in LY294002-pretreatment crayfish was significantly higher than that of crayfish pretreated with Tris-HCl on the third or sixth day, but the Toll and lectin mRNA expression decreased significantly on the third, sixth and tenth day. The Bax mRNA expression levels in LY294002-WSSV group were significantly higher than those in Tris-HCl-WSSV group on the third and tenth day. The Bax inhibitor-1 mRNA expression levels in LY294002-WSSV group were significantly lower than those in Tris-HCl-WSSV crayfish on the third day. These results together indicated that the hosts PI3K/AKT signaling pathway play positive roles in WSSV replication through the balance between host cell apoptois and innate immune responses. This information is helpful to further understand the role of PI3K/AKT signaling pathway on WSSV replication in Decapoda crustaceans. [ABSTRACT FROM AUTHOR]

The application of a potentiometric pH electrode in ocean acidification observation is still a challenge due to its poor sensitivity to small pH changes. Herein, a simple approach to remarkably improve the detection precision of a polymeric membrane ion-selective electrode is proposed based on the potential-modulated ion transfer mechanism. The present sensing strategy displays highly sensitive responses to small pH changes for seawater analysis with a precision of 5 μpH, which is 2 orders of magnitude lower than that of the conventional pH electrode.

Nowadays, using a potentiometric ion sensor to achieve detection of biological analytes is still a big challenge, since these analytes usually do not yield a measurable ion signal. To address this challenge, a simple and robust potentiometric sensing protocol based on a delayed Nernstian response is proposed for the label-free detection of biological analytes. The proposed sensor platform is composed of two layers: the surface recognition layer and the indicator-ion-selective electrode (ISE) membrane layer. It is based on a surface blocking mechanism in which the surface recognition interactions between the surface recognition element and the target can impede the diffusion of the indicator ion from the aqueous phase to the sensing membrane phase to reach the final Nernstian-response equilibrium, thus resulting in a delayed potential change. Such a potential change could be used to measure the concentration of a biological target in the sample. Thus, a sensing system was designed by using phage MS2, its host bacterium Escherichia coli ATCC 15597(abbreviated as E. coli H), and a solid-contact butyrylcholine ISE as a surface recognition element, a target, and an indicator electrode, respectively. This new concept offers a simple, sensitive, and extremely selective potentiometric method for detection of E. coli H with a detection limit of 100 CFU mL -1 . It can be expected that the present approach may pave the way to using ISEs to detect various important nonionic biological targets in clinical and environmental applications.

Currently, Nernstian-response-based polymeric membrane potentiometric sensors using molecularly imprinted polymers (MIPs) as receptors have been successfully developed for determination of organic ionic species. However, the preparation of these MIP receptors usually involves tedious and time-consuming template-removal procedures. Herein, a template-removal-free MIP is proposed and used as a receptor for fabrication of a potentiometric sensor. The proposed methodology not only significantly shortens the preparation time of MIP-based potentiometric sensors but also improves the batch-to-batch reproducibility of these sensors. By using antibiotic vancomycin as a model, the new concept offers a linear concentration range of 1.0 × 10 -7 to 1.0 × 10 -4 mol L -1 with a detection limit of 2.51 × 10 -8 mol L -1 . It can be expected that the template-removal-free MIP-based sensing strategy could lay the foundation for simple fabrication of electrochemical sensors without the need for template removal such as potentiometric and capacitive sensors and ion-sensitive field-effect transistors.

Nowadays, using a polymeric membrane ion-selective electrode (ISE) to achieve reliable ion sensing in complex samples remains challenging because of electrode fouling. To address this challenge, we describe a polymeric membrane ISE with excellent anti-fouling and self-cleaning properties based on surface covalent modification of an anatase TiO 2 coating. Under ultraviolet illumination, the reactive oxygen species produced by photocatalytic TiO 2 can not only kill microorganisms but also degrade organic foulants into carbon dioxide and water, and a formed superhydrophilic film can effectively prevent the adsorption of foulants, thus inhibiting the occurrence of biofouling and organic fouling of the sensors. More importantly, residual foulants could be fully self-cleaned through the flow of water droplets. By using Ca 2+ -ISE as a model, an anti-fouling polymeric membrane potentiometric sensor has been developed. Compared to the unmodified electrode, the TiO 2 -coated Ca 2+ -ISE exhibits remarkably improved anti-biofouling properties with a low bacterial adhesion rate of 4.74% and a high inhibition rate of 96.62%. In addition, the proposed electrode displays unique properties of anti-organic dye fouling and a superior self-cleaning ability even after soaking in a concentrated bacterial suspension of 10 9 CFU mL -1 for 60 days. The present approach can be extended to improve the fouling resistance of other electrochemical or optical membrane sensors and is promising for the construction of contamination-free sensors.

Due to the frequent oil spill accidents and pollution of industrial oily wastewater, oil fouling has become a great challenge to polymeric membrane ion-selective electrodes (ISEs) for applications in oil-contaminated areas. Herein, a simple approach is proposed to enhance the oil-fouling resistance of polymeric membrane ISEs by surface modification of a zwitterionic polymer-based underwater oleophobic coating. As a proof-of-concept, a classical poly(vinyl chloride) membrane-based calcium ion-selective electrode (Ca 2+ -ISE) is chosen as a model sensor. The zwitterionic polymer-based coating can be readily modified on the sensor's surface by immersion of the electrode into a mixture solution of dopamine and a zwitterionic acrylate monomer (i.e., sulfobetaine methacrylate, SBMA). The formed poly(SBMA) (PSBMA) coating alters the oleophilic membrane surface to an oleophobic one, which endows the surface with excellent self-cleaning properties without loss of the sensor's analytical performance. Compared to the pristine Ca 2+ -ISE, the PSBMA-modified Ca 2+ -ISE exhibits an improved analytical stability when exposed to oil-containing wastewater. The proposed approach can be explored to enhance the oil-fouling resistance of other polymeric membrane-based electrochemical sensors for use in the oil-polluted environment.

Nowadays, polymeric membrane potentiometric sensors based on the molecularly imprinted polymers (MIPs) have been successfully developed for detection of various organic and biological species. However, it is difficult for these sensors to perform reversible detection of the targets due to the high affinities of the MIPs toward the targets. In this work, we propose a novel method for fully reversible potentiometric detection of neutral phenols based on the stimulus-responsive MIP as the selective receptor. Since such smart receptor can switch its recognition abilities according to the external environmental stimuli, the MIP binding sites in the polymeric membrane can be regenerated via the stimulus after each measurement. Thus, potentiometric reversible detection of the target can be achieved. As a proof of concept, the pH-responsive MIP is used as the selective receptor, which can be synthesized by using 4-vinylphenylboronic acid as the functional monomer. The boronate-affinity MIP can covalently bind with a cis -diol containing compound to form a five- or six-membered cyclic ester in a weakly alkaline aqueous solution, while the produced ester dissociates when the surrounding pH is changed to acidic. By using catechol as a model, the proposed smart sensor exhibits a significantly improved reversibility compared to the conventional MIP-based sensor. We believed that the stimulus-responsive MIP-based sensing strategy could provide an appealing way to design reversible MIP-based electrochemical and optical sensors.

Nowadays, it is still difficult for molecularly imprinted polymers (MIPs) to achieve homogeneous recognition since they cannot be easily dissolved in organic or aqueous phase. To address this issue, soluble molecularly imprinted nanorods have been synthesized by using soluble polyaniline doped with a functionalized organic protonic acid as the polymer matrix. By employing 1-naphthoic acid as a model, the proposed imprinted nanorods exhibit an excellent solubility and good homogeneous recognition ability. The imprinting factor for the soluble imprinted nanoroads is 6.8. The equilibrium dissociation constant and the apparent maximum number of the proposed imprinted nanorods are 248.5 μM and 22.1 μmol/g, respectively. We believe that such imprinted nanorods may provide an appealing substitute for natural receptors in homogeneous recognition related fields.

Molecularly imprinted polymer (MIP)-based polymeric membrane potentiometric sensors have been successfully developed for determination of organic compounds in their ionic and neutral forms. However, most of the MIP receptors in potentiometric sensors developed so far are insoluble and cannot be well dissolved in the polymeric membranes. The heterogeneous molecular recognitions between the analytes and MIPs in the membranes are inefficient due to the less available binding sites of the MIPs. Herein we describe a novel polymeric membrane potentiometric sensor using a soluble MIP (s-MIP) as a receptor. The s-MIP is synthesized by the swelling of the traditional MIP at a high temperature. The obtained MIP can be dissolved in the plasticized polymeric membrane for homogeneous binding of the imprinted polymer to the target molecules. By using neutral bisphenol AF as a model, the proposed method exhibits an improved sensitivity compared to the conventional MIP-based sensor with a lower detection limit of 60 nM. Moreover, the present sensor exhibits an excellent selectivity over other phenols. We believe that s-MIPs can provide an appealing substitute for the traditional insoluble MIP receptors in the development of polymeric membrane-based electrochemical and optical sensors.

Polymeric membrane ion-selective electrodes (ISEs) have become attractive tools for trace-level environmental and biological measurements. However, applications of such ISEs are often limited to measurements with low levels of electrolyte background. This paper describes an asymmetric membrane rotating ISE configuration for trace-level potentiometric detection with a high-interfering background. The membrane electrode is conditioned in a solution of interfering ions (e.g., Na(+)) so that no primary ions exist in the ISE membrane, thus avoiding the ion-exchange effect induced by high levels of interfering ones in the sample. When the electrode is in contact with the primary ions, the interfering ions in the membrane surface can be partially displaced by the primary ions due to the favorable ion-ligand interaction with the ionophore in the membrane, thus causing a steady-state potential response. By using the asymmetric membrane with an ion exchanger loaded on the membrane surface, the diffusion of the primary ions from the organic boundary layer into the bulk of the membrane can be effectively blocked; on the other hand, rotation of the membrane electrode dramatically reduces the diffusion layer thickness of the aqueous phase and significantly promotes the mass transfer of the primary ions to the sample-membrane interface. The induced accumulation of the primary ions in the membrane boundary layer largely enhances the nonequilibrium potential response. By using copper as a model, the new concept offers a subnanomolar detection limit for potentiometric measurements of heavy metals with a high electrolyte background of 0.5 M NaCl.