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

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

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

Improvement of the selectivity of a molecularly imprinted polymer-based potentiometric sensor by using a specific functional monomer

Potentiometric sensors based on the molecularly imprinted polymers (MIPs) as the receptors have been successfully developed for determination of various organic and biological species. However, these MIP receptors may suffer from problems of low selectivity. Especially, it would be difficult to distinguish the target analyte from its structurally similar interferents. In this work, we propose a novel strategy that using specific functional monomer to fabricate MIP with high selectivity towards the target molecule. The density functional theory calculations are used to investigate the interactions between the template and the functional monomer. The binding energy between the template and functional monomer can be used as the criterion for identifying the optimal monomer. As a proof-of-concept experiment, bisphenol A (BPA) is chosen as the template and the MIP is synthesized by the precipitation polymerization method using the specific allyl-beta-cyclodextrin (allyl-beta-CD) with high affinity towards BPA as the functional monomer. The high-affinity MIP is employed as the receptor for the construction of the potentiometric sensor. The proposed potentiometric sensor based on the MIP using allyl-beta-CD as the functional monomer shows an improved response performance in terms of selectivity and sensitivity compared to the conventional potentiometric sensor based on the MIP with the common monomer (i.e., methacrylic acid). This allyl-beta-CD MIP-based potentiometric sensor shows a detection limit of 0.29 mu M for BPA, which is about one order of magnitude lower than that obtained by the conventional MIP-based potentiometric sensor. We believe that utilizing a functional monomer with specific recognition ability towards target in the fabrication of MIP could provide an appealing way to construct highly selective 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

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 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

Environmentally friendly anti-biofouling polymeric membrane potentiometric sensors based on imprinted receptors

Polymeric membrane potentiometric sensors using molecularly imprinted polymer (MIP) receptors are an ideal tool for determination of organic ionic species. However, their applications in complicated samples are very limited because of occurrence of sensor biofouling. Herein, for the first time, we describe a simple but environmentally friendly strategy to improve anti-biofouling performance of MIP-based potentiometric sensors. The non-toxic, environmentally friendly anti-fouling agent is doped into the polymeric membrane. The released organic biocidal agent from the polymeric membrane can kill the microorganisms adhered to the sensing membrane surface, and the formation of biofilms can thus be prevented. As a proof-the-concept experiment, an all-solid-state MIP-based potentiometric ceftiofur sensor is selected as a model. Capsaicin, a naturally occurring alkaloid derived from chillis, is chosen as a non-toxic biocide agent. Another widely used biocide agent 4,5dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) with low toxicity is also used as a comparison. Compared to the undoped electrode, the capsaicin-doped MIP sensor exhibits remarkably improved anti-biofouling abilities in terms of the low survival rates and the low adhesion rates of the bacterial cells and microalgae. Especially, the capsaicin-based electrode displays similar anti-fouling and response properties to the DCOIT-based one. It can be anticipated that such anti-fouling strategy may lay the foundation for development of "green" anti-fouling sensors, which are urgently required in marine monitoring and clinical diagnosis