Detection of Bromide Ions in Water Samples with a Nanomolar Detection Limit using a Potentiometric Ion-selective Electrode

This paper presents a robust potentiometric solid-contact ion-selective electrode (ISE) for the rapid detection of bromide ions (Br-) in water samples. The sensing membrane contains poly (vinyl chloride) (PVC), bis(2-ethylhexyl)sebacate (DOS) and ionophore without a lipophilic ion exchanger, and provides good potential responses for Br- in the range of 0.010 to 1.0 mu M. The calibration curve demonstrates detection limits of 2.0x 10(-9) mol/L (3 sigma) for bromide ions. Moreover, compared with previously reported Br-selective ISEs, the proposed ISE offers remarkably improved sensitivity for the detection of bromide and provides better selectivity coefficients for HPO42-, CH3COO-, NO3-, and Cl-. The proposed sensor is successfully applied for the practical determination of Br- in real water samples

Molecularly imprinted polymer-based potentiometric sensors

Carrier-based polymeric membrane potentiometric sensors have been widely used for determination of inorganic ions in clinical and environmental applications. In view of the need for a wider application scope of these sensors, the list of targets needs to be increased. Molecularly imprinted polymer (MIP)-based potentiometric sensors are ideal candidates for sensing of organic and biological species. The development of such sensors may open attractive horizons for potentiometric sensing and further expand the field. The past few decades have witnessed remarkable achievements in these sensors. This review summarizes recent advances in the MIP synthesis, the detection modes of these sensors and their applications for organic and biological species in environmental and biological analyses, and attempts to illustrate the research directions. We hope that this review will shed new light on the understanding of MIP-based potentiometric sensors and pave the way for the widespread applications of polymeric membrane potentiometric sensors. (C) 2020 Elsevier B.V. All rights reserved

A molecularly imprinted polymer-based potentiometric sensor based on covalent recognition for the determination of dopamine

Polymeric membrane potentiometric sensors based on molecularly imprinted polymers (MIPs) have been successfully designed for the detection of organic compounds both in ionic and neutral forms. However, most of these sensors are based on the non-covalent recognition interactions between the functional groups of the MIP in the polymeric sensing membrane and the target. These weak non-covalent interactions are unfavorable for the detection of hydrophilic organic compounds (e.g., dopamine). Herein novel MIP potentiometric sensor based covalent recognition for the determination of protonated dopamine is described. Uniform-sized boronate-based MIP beads are utilized as the recognition receptors. These receptors can covalently bind with dopamine with a cis-diol group to form a five-membered cyclic ester and thus provide a higher affinity because of the stronger nature of the covalent bonds. It has been found that the proposed electrode shows an excellent sensitivity towards dopamine with a detection limit of 2.1 mu M, which could satisfy the needs for in vivo analysis of dopamine in the brain of living animals. We believe that the covalent recognition MIP-based sensing strategy provides an appealing way to design MIP-based electrochemical and optical sensors with excellent sensing properties

Thin polymeric membrane ion-selective electrodes for trace-level potentiometric detection

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 mm, 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 mm. 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. (C) 2020 Elsevier B.V. All rights reserved

Potentiometric sensor based on a computationally designed molecularly imprinted receptor

Molecularly imprinted polymer (MIP)-based polymeric membrane potentiometric sensors are ideal candidates for detection of organic species. The development of such sensors has opened new attractive horizons for potentiometric sensing. However, it should be noted that in the preparation of these MIP receptors, the selection of the functional monomer usually depends on empirical trial-and error-based optimization, which involves tedious and time-consuming experiments. In this work, the computer-aided design and synthesis of an MIP re-ceptor are applied in the fabrication of an MIP-based potentiometric sensor. The density functional theory calculation with the B3LYP model and 6-31G(d) basis set is used to study the interactions between the functional monomer and template molecules. The binding energies of the complexations between the template molecule and different functional monomers are used as a criterion for the selection of the proper monomer. The designed MIP is then synthesized and employed as the receptor for the fabrication of the potentiometric sensor. As a proof -of-concept experiment, the antibiotic sulfadiazine has been selected as a model and 4 functional monomers, 2-hydroxyethyl methacrylate, methyl methacrylate, N-isopropylacrylamide and N-phenylacrylamide, have been chosen. The designed MIP-based sensor exhibits excellent sensitivity with a linear range of 1-10 mu M and also shows a good selectivity. We believe that the proposed computer-aided synthesis technique for the MIP receptor selection can provide a general and facile way to replace the traditional empirical MIP preparation method in the fabrication of MIP-based electrochemical and optical sensors

Towards potentiometric detection in nonaqueous media: Evaluation of the impacts of organic solvents on polymeric membrane ion-selective electrodes

Polymeric membrane ion-selective electrodes (ISEs) have been widely used in various fields including clinical diagnosis, environmental monitoring and industrial analysis. Although most samples of analytical interest measured by the ISEs are aqueous solutions, the applications of these electrodes in nonaqueous media are often inevitable. Unfortunately, so far, little has been known about the extent to which the properties of the ISEs could be affected by the organic solvents. Herein, the feasibility for the applications of the polymeric membrane ISEs in nonaqueous media has been investigated. A polymeric membrane Ca2+-ISE is chosen as a model of potentiometric sensors. Four typical water miscible organic solvents (three protic solvents: ethanol, acetic acid, and methanol, and one aprotic dipolar solvent: acetonitrile) are used as the representative examples. Experiments show that the aprotic solvent acetonitrile has the strongest destructive ability towards the sensing performance of the ISE in terms of Nernstian slope and selectivity coefficient. Moreover, the effect on the sensing performance depends on the kind of the protic solvent, the immersion time and the polarity of the membrane plasticizer. We believe that the obtained results could promote further applications of the polymeric membrane ISEs in the organic solvent-containing samples, which could significantly extend the application scope of the ISEs

Potentiometric sensor based on molecularly imprinted polymer for determination of melamine in milk

A polymeric membrane ion-selective electrode for determination of melamine is described in this paper. it is based on a molecularly imprinted polymer (MIP) for selective recognition, which can be synthesized by using melamine as a template molecule, methacrylic acid as a functional monomer and ethylene glycol dimethacrylate as a cross-linking agent. The membrane electrode shows near-Nernstian response (54 mV/decade) to the protonated melamine over the concentration range of 5.0 x 10(-6) to 1.0 x 10(-2) mol L(-1). The electrode exhibits a short response time of similar to 16 s and can be stable for more than 2 months. Combined with flow analysis system, the potentiometric sensor has been successfully applied to the determination of melamine in milk samples. Interference from high concentrations of ions co-existing in milk samples such as K(+) and Na(+) can be effectively eliminated by on-line introduction of anion- and cation-exchanger tandem columns placed upstream, while melamine existing as neutral molecules in milk of pH 6.7 can flow through the ion-exchanger columns and be measured downstream by the proposed electrode in an acetate buffer solution of pH 3.7. (C) 2009 Elsevier BY. All rights reserved

Stimulus-Responsive Imprinted Polymer-Based Potentiometric Sensor for Reversible Detection of Neutral Phenols

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