Solid contact potassium selective electrodes for biomedical applications - a review

Ion-selective electrodes (ISE) are used in several biomedical applications, including laboratory sensing of potassium concentration in blood and urine samples. For on-site determination of potassium concentration and usage in other applications such as determination of extracellular potassium concentration, miniaturization of the sensors is required. To that extent, solid contacts have proven to be an adequate substitute of liquid contacts as inner layer for ion-to-electron transduction, allowing industrial production of miniaturized ISEs. This review paper covers relevant developments of solid-state ISEs in the past decade, critically compares current potassium ISEs and discusses future prospects for biomedical applications. Performances of three main types of solid contact materials in potassium sensing are compared, namely polypyrrole, polythiophenes and conducting nanomaterials. With these new materials, numerous improvements in stability, selectivity and time response of solid-state ISEs have been made. Current developments are new operational methods of sensing, flexible miniaturized sensors and multi-electrode designs able to measure electrolyte concentrations in one-drop blood samples or transmembrane ionic flows.

Electropolymerized hydrophobic polyazulene as solid-contacts in potassium-selective electrodes

Electropolymerized hydrophobic polyazulene based solid-contact potassium-selective electrodes have been characterized in terms of their suitability for potassium measurements in serum.

Supramolecular biosensors based on electropolymerised pyrrole–cyclodextrin modified surfaces for antibody detection

The self-assembly of an adamantane-appended polymer bearing an antigen fragment on a polypyrrole–cyclodextrin modified surface provides a highly sensitive immunosensor with low limits of detection for celiac disease related antibodies.

Potentiometric determination of pantoprazole using an ion-selective sensor based on polypyrrole doped films

The present work reports for the first time the use of polypyrrole (PPy) doped film for development of a potentiometric disposable sensor for determination of pantoprazole (PTZ), a drug used for ulcer treatment. Selective potentiometric response has been found by using a membrane of PPy doped with PTZ anions prepared under galvanostatic conditions at graphite pencil electrode (GPEM/PPy-PTZ) surface. Potentiometric response has been influenced for conditions adopted in polymerization and measurement step. After optimization of experimental (e.g. pH and time of conditioning) and instrumental parameters (e.g. current density and electrical charge) a linear analytical curve from 1.0 × 10(-5) to 1.1 × 10(-2) mol L(-1) with a slope of calibration of the 57.6 mV dec(-1) and limit of detection (LOD) of 6.9 × 10(-6) mol L(-1) was obtained. The determination of the PTZ content in pharmaceutical samples using the proposed methodology and official method recommended by Brazilian Pharmacopeia are in agreement at the 95% confidence level and within an acceptable range of error.

Ion-selective organic electrochemical transistors

Ion-selective organic electrochemical transistors with sensitivity to potassium approaching 50 μA dec(-1) are demonstrated. The remarkable sensitivity arises from the use of high transconductance devices, where the conducting polymer is in direct contact with a reference gel electrolyte and integrated with an ion-selective membrane.

Miniaturizable ion-selective arrays based on highly stable polymer membranes for biomedical applications

Poly(vinylchloride) (PVC) is the most common polymer matrix used in the fabrication of ion-selective electrodes (ISEs). However, the surfaces of PVC-based sensors have been reported to show membrane instability. In an attempt to overcome this limitation, here we developed two alternative methods for the preparation of highly stable and robust ion-selective sensors. These platforms are based on the selective electropolymerization of poly(3,4-ethylenedioxythiophene) (PEDOT), where the sulfur atoms contained in the polymer covalently interact with the gold electrode, also permitting controlled selective attachment on a miniaturized electrode in an array format. This platform sensor was improved with the crosslinking of the membrane compounds with poly(ethyleneglycol) diglycidyl ether (PEG), thus also increasing the biocompatibility of the sensor. The resulting ISE membranes showed faster signal stabilization of the sensor response compared with that of the PVC matrix and also better reproducibility and stability, thus making these platforms highly suitable candidates for the manufacture of robust implantable sensors.

Improved thin-layer electrolysis cell for ion transfer at the liquid|liquid interface using a conducting polymer-coated electrode

This article reviews the development of a thin-layer electrolysis cell with both a thin aqueous phase and a thin organic phase for ion transfer at the liquid|liquid interface for the absolute determination of a redox-inactive ion. In particular, an improvement of the cell performance by using a conducting polymer-coated electrode in the organic phase is discussed. The applicability of the thin-layer electrolysis cell to the absolute determination of redox-inactive ions using the flow-injection method or stripping method is also described.

Effective solid contact for ion-selective electrodes: tetrakis(4-chlorophenyl)borate (TB-) anions doped nanocluster films

We report on a novel material, tetrakis(4-chlorophenyl)borate (TB(-)) anion doped nanocluster films, as the solid contact (SC) for producing well-defined, electrochemically reversible, and nonpolarizable double interfaces on it. Detailed studies have unambiguously revealed that, for the first time, the developed SC can fully overcome all the signal stability problems of ion-selective electrodes (ISEs), offering a reliable and universal platform for the development of high quality SC-ISEs. As an exemplification, the developed monolayer-protected cluster (MPC) based K(+)-ISEs have advantages of excellent analytical performances, e.g., the low potential drift (10.1 ± 0.3 μV h(-1) over 72 h measured in 0.1 M KCl and 10.8 ± 0.5 μV h(-1) over 96 h rechecked in 0.1 M KCl after 1 month) and the stable and reproducible linear range, sensitivity, and standard potential (few changes within the first 6 weeks). This evidence suggests that the developed MPC films are the most promising SC transducers among all the reported ones to the best of our knowledge.

Stimuli responsive ionogels for sensing applications-an overview

This overview aims to summarize the existing potential of "Ionogels" as a platform to develop stimuli responsive materials. Ionogels are a class of materials that contain an Ionic Liquid (IL) confined within a polymer matrix. Recently defined as "a solid interconnected network spreading throughout a liquid phase", the ionogel therefore combines the properties of both its solid and liquid components. ILs are low melting salts that exist as liquids composed entirely of cations and anions at or around 100 °C. Important physical properties of these liquids such as viscosity, density, melting point and conductivity can be altered to suit a purpose by choice of the cation/anion. Here we provide an overview to highlight the literature thus far, detailing the encapsulation of IL and responsive materials within these polymeric structures. Exciting applications in the areas of optical and electrochemical sensing, solid state electrolytes and actuating materials shall be discussed.

Combinatorial and high-throughput screening of materials libraries: review of state of the art

Rational materials design based on prior knowledge is attractive because it promises to avoid time-consuming synthesis and testing of numerous materials candidates. However with the increase of complexity of materials, the scientific ability for the rational materials design becomes progressively limited. As a result of this complexity, combinatorial and high-throughput (CHT) experimentation in materials science has been recognized as a new scientific approach to generate new knowledge. This review demonstrates the broad applicability of CHT experimentation technologies in discovery and optimization of new materials. We discuss general principles of CHT materials screening, followed by the detailed discussion of high-throughput materials characterization approaches, advances in data analysis/mining, and new materials developments facilitated by CHT experimentation. We critically analyze results of materials development in the areas most impacted by the CHT approaches, such as catalysis, electronic and functional materials, polymer-based industrial coatings, sensing materials, and biomaterials.