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In this work, a potentiometric polyion sensing strategy based on the surface layer-enhanced transmembrane ion transfer is demonstrated. A polydopamine (PDA) nanolayer with negative charges is modified onto the surface of the polycation-sensitive electrode membrane and used to increase the ion fluxes from the sample phase to the membrane phase. Such modification can significantly improve the detection sensitivity of potentiometric polyion sensors through electrostatic interactions between the cationic targets and anionic PDA groups, which can effectively promote the accumulation of the targets in the boundary layer of the organic membrane phase. By using a thin membrane protamine-sensitive electrode as a model, the detection sensitivity of the PDA-coated electrode (55 mV/μg·mL−1) is nearly five times higher than that of the unmodified electrode (12 mV/μg·mL−1). Moreover, the proposed surface PDA-modified polyion sensor can also be utilized as a general tool for sensitive detection of other polycationic targets and polyanionic species (e.g., the new cancer biomarker cell-free DNA). The proposed potentiometric sensing platform based on surface enhancement of ion transfer offers great potential for sensitive detection of various polyionic targets. [Display omitted] • A surface PDA nanolayer is used to enhance the transmembrane ion transfer of potentiometric polyion sensors. • Such modification can significantly improve detection sensitivity of polycation-sensitive electrodes. • The detection sensitivity of the PDA-coated electrode is nearly five times higher than that of the unmodified one. • Beyond protamine, the proposed sensor can be utilized as a general tool for sensitive detection of other polyions. • The concept may pave the way to using PSEs for sensitive detection of a variety of polyionic biological targets. [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]

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. [Display omitted] • Feasibility for application of polymeric membrane ISEs in nonaqueous media is tested. • Effect of water-miscible organic solvents on ISE sensing performance is investigated. • Aprotic solvent has a stronger destructive ability towards ISE than protic solvent. • Leaching of the membrane components in organic solution is quantified for the first time. • The present work may lay a foundation for application of ISEs in nonaqueous samples. [ABSTRACT FROM AUTHOR]

Reliable potentiometric ion sensing in complex samples (e.g., biological fluids, wastewater and seawater) remains a great challenge for polymeric membrane ion-selective electrodes (ISEs). As one of the major impediments, electrode fouling which is caused by the undesirable adsorptions of organic molecules and biological cells on the electrode surfaces can seriously impair the analytical performance of ISEs. Development of polymeric membranes with fouling resistance is a fundamental strategy to deal with this ubiquitous problem. To date, it has become an important research direction for applications of polymeric membrane ISEs. This paper presents an overview on the advances in anti-fouling ISEs. The major foulants for polymeric membrane ISEs and the fouling influences on the sensors' performance are described. The anti-fouling strategies, preparation methods and future prospects for antifouling ISEs are discussed. • An overview on the advances in anti-fouling polymeric membrane ion-selective electrodes is presented. • Major foulants and their influences on polymeric membrane ion-selective electrodes are summarized. • Anti-fouling strategies of polymeric membrane ion-selective electrodes are discussed. • Preparation methods of anti-fouling polymeric membrane ion-selective electrodes are summarized. • Future directions in development of anti-fouling polymeric membrane ion-selective electrodes are provided. [ABSTRACT FROM AUTHOR]

Abstract: 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 (54mV/decade) to the protonated melamine over the concentration range of 5.0×10−6 to 1.0×10−2 molL−1. The electrode exhibits a short response time of ∼16s 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. [Copyright &y& Elsevier]

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]