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We report on successful preparation of conducting polymer nanofibers from regiorandom poly(3‐hexylthiophene). It is shown that the electrochemical properties of obtained structures are significantly improved in course of electrochemical doping process performed in the aqueous phase, moreover this process is accompanied with change of optical properties and water contact angle. These effects are not observed for polymer films. Moreover, doping of nanofibers results in pronounced, irreversible changes in the polymer structure – increased crystallinity due to incorporation of doping ions is confirmed by optical and X‐ray crystallographic studies. Ultimately, these changes lead to decreased resistance and improved electrochemical performance of nanofibers mat. As this effect is solely observed for nanofibers of conducting polymer, it can be ascribed to high surface to volume ratio of electrospun fibers mat. Therefore, it is shown for the first time that polythiophene electrochemical doping process effect is dependent on the format of the polymer applied, for nanofibers it can be regarded as attractive method of improving electrochemical properties of polymers. [ABSTRACT FROM AUTHOR]

The applicability of emission readout of ion‐selective electrodes, containing fluorimetrically active polyoctylthiophene in the membrane, operating under chronopotentiometric mode was studied. The electrochemical and optical signals were collected in the same experiment and compared. In both modes a change in recorded signal: potential or emission in time was observed while a constant current was applied to the sensor. The recorded signals (chronopotentiometric, fluoro‐chronopotentiometric curves and calculated transition times) were dependent on the concentration of potassium ions. The transition times calculated from electrochemical signals were linearly dependent on the concentration of potassium ions in solution within the range: 0.1–0.7 mM. Optically read transition times were also linearly dependent on concentration within the same range, however, they were shorter than those recorded electrochemically. This difference is attributed to various effects represented by the transition time: concentration increase of reduced form of the conducting polymer in the optical mode or depletion of potassium ions close to the membrane surface, in the electrochemical mode. [ABSTRACT FROM AUTHOR]

Applicability of a bipolar electrode system was tested for arrangements containing a typical ion‐selective electrode (ISE) connected with an electrode coated by a conducting polymer characterized by electroluminescence. In this case a selective response of the ISE membrane at one pole of the bipolar electrode is transduced to a fluorimetric signal obtained by reduction of the conducting polymer at the second pole. This signal transformation mode was studied on example of a simple closed bipolar electrode system composed of all‐solid‐state chloride‐selective electrode with polypyrrole transducer as the sensing pole and the reporting pole represented by electrode coated by poly(3‐octylthiophene) (POT) layer characterized by fluorescence in the neutral state. In this system selective and linear dependences of fluorimetric signal on logarithm of chloride ions concentration in turn‐on mode were recorded for optimized external voltage applied. Alternatively, a concept of cascade bipolar electrode system with incorporation of additional bipolar electrode being a polarization source for the sensing bipolar electrode with ISE and POT layer was also tested. A significant advantage of the cascade system is its possibility to work spontaneously without external polarization. For this case also linear calibration plots of fluorimetric signal vs. logarithm of analyte concentration were recorded. [ABSTRACT FROM AUTHOR]

Polyoctylthiophene electrochemical and optical properties are dependent on the polymer oxidation state, generally requiring presence of doping ions. In this work polyoctylthiophene composites with pyrene or aminopyrene have been prepared and studied using optical and electrochemical methods. It is shown that in the composite formed pyrene molecules act as molecular dopant for the conducting polymer, resulting in a system of partially oxidized polythiophene backbone, yet of high lipophilicity. On the other hand, composite of aminopyrene with polyoctylthiophene is characterized with pH dependent electrochemical and optical properties. The difference arises mostly from the protonation/ deprotonation reaction occurring for aminopyrene embedded in polyoctylothiophene. Nanoparticles of polythiophene‐aminopyrene show turn‐on emission dependence on increase of hydrogen ions concentration in solution in a wide pH range from 12 to 5. For low pH high emission activity is observed for nanoparticles, whereas for films high lipophilicity and low electrochemical activity pointing to presence of semiconducting polymer in the system for protonated aminopyrene. For high pH, when deprotonation of aminopyrene is observed, the system is characterized with low optical, yet high electrochemical activity and low lipophilicity. The electrochemical activity of polyoctylthiophene‐aminopyrene composite can be reversibly switched simply by solution pH change. [ABSTRACT FROM AUTHOR]

In this work a novel concept of monitoring of occurrence of redox reactions between conducting polymer nanospheres and redox species in a solution is proposed. The redox process is monitored in the emission mode (without wiring of the probe to an electrochemical measuring set-up) as a change in emission spectrum of a dye (not participating in the redox process itself) but reporting the alteration of properties of highly sensitive conducting polymer nanoparticles. This approach is possible due to applied unique method of synthesis of conducting polymers nanospheres of highly active, unblocked surface. Thus the nanospheres redox state is affected by the solution redox potential, leading to change of their properties. If solvatochromic probe of sufficiently high brightness (pyrene) is present in nanospheres, a redox reaction between the conducting polymer and solution can be observed as change of emission spectrum of the probe. Thus a localized redox potential optical probe can be obtained. The emission properties of the dye incorporated were preserved in the nanospheres, moreover, the emission spectrum of the probe was affected by the change in redox potential of the solution, thus influencing the redox state and ultimately the properties of the conducting polymer. The emission changes observed were dependent on ion-exchange properties of polypyrrole, i.e. depending on the dopant ions present in the polymer, the sensitivity of the optical probe can be tuned. [ABSTRACT FROM AUTHOR]

All-solid-state ion-selective electrodes with conducting polymer solid contact represent good analytical parameters, comparable with those of classical sensors with internal filling solution. One of parameters characterizing quality of the solid contact, related to ion-to-electron transduction, is the electrical capacitance. However, in many cases this capacitance is lower than for the solid contact only, in the absence of ion-selective membrane. This effect can be disadvantageous, particularly for sensors working under polarization conditions, in galvanostatic mode. The capacitance reduction effect was studied on example of model systems of anion- and cation-selective electrodes with poly(3,4-ethylenedioxythiophene) solid contact with anion- or cation-exchange properties. Basing on results obtained for these membranes and contacts as well as some model calculations, the reasons of reduced capacitance were ascribed to low amount of ions transferrable across the solid contact/membrane interface. This effect can result from low concentration of mobile ions in the conducting polymer contact or concentration polarization effects. Procedures or pretreatment methods were proposed to minimize the effect of capacitance decrease. [ABSTRACT FROM AUTHOR]

In this work the problem of upper detection limit of potentiometric sensors is addressed. Due to deviation of potentiometric plots from cationic Nernstian responses determination of analytes like silver cations in concentrations above 10−2 M is hardly possible, especially in the presence of background electrolyte containing lipophilic anions. Herein proposed approach applied classical complexing ligand, dithizone, attached to gold nanoparticles as ionophore. Immobilization on gold nanoparticles surface effectively anchores ligand molecules within the membrane phase. Thus obtained sensors are characterized with stable, Nernstian, potentiometric responses and selectivity comparable with classical membrane compositions. Moreover, due to lower formation constant of Ag+ with dithizone based ligand, herein reported sensors offer linear, Nernstian responses also in the range of high activity of AgNO3 solutions. [ABSTRACT FROM AUTHOR]

Simple conducting polymer–polyaniline-based sensors/biosensors, working either in potentiometric or UV/Vis spectrophotometric mode, are proposed. Disposable sensors were produced by coating polyaniline layers, cast from aqueous dispersion of the polymer nanoparticles, on a transparent plastic polyacetate foil. In the potentiometric mode, polyaniline layers are sensitive to a number of metal cations, while in UV/Vis mode, changes of absorbance were recorded only in case of a chemical reaction of cations with the polymer. Pronounced sensitivity of tested sensors to ammonia was used for potentiometric/spectrophotometric biosensing purposes studied on a model example of urease-based sensors of urea. The highest sensitivity and reproducibility of such sensors were observed in urea concentration ranging from 1 to 10 mM. [ABSTRACT FROM AUTHOR]

Abstract: Comparison of potentials stability of different types of solid contact lead selective electrodes is presented. Conducting polymer based sensors (hydrophilic and conducting – poly(3,4-ethylenedioxythiophene) or hydrophobic and semiconducting-polyoctylthiophene) were studied in parallel with coated wire and hydrogel (poly(hydroxyethylmethacrylate)) contact electrodes. The within day and between days potential stability was compared, highlighting the effect of sensor storing conditions. The obtained results clearly demonstrate that different conclusions on stability of sensors’ potential can be drawn depending on experimental protocol applied. Polyoctylthiophene based contacts show superior within day stability with no influence of dry storage. On the other hand, a chronopotentiometric method of stability evaluation clearly prefers poly(3,4-ethylenedioxythiophene) based sensors, pointing to smallest resistance and polarizability. It is clearly shown that the choice of experimental conditions applied to test stability can favor particular type of contact used. The inductively coupled plasma mass spectrometry with laser ablation (LA-ICP-MS) experiments conducted for different arrangements tested has shown that for poly(3,4-ethylenedioxythiophene) and poly(hydroxyethylmethacrylate) type contacts longer contact time with lead(II) solution results in changes in the elemental composition of the transducer layer. On the other hand, in line with high stability observed under potentiometric conditions, no changes were seen for polyoctylthiophene based transducer. [Copyright &y& Elsevier]

Abstract: Electrochemical properties of poly(3,4-ethylenedioxythiophene) doped with hexacyanoferrate(II,III) ions (PEDOT(HCF)) were studied in the presence of Cu2+ ions. Voltammetric and EDAX studies revealed retention of hexacyanoferrate anions in the polymer film and accumulation of Cu(II) cations, as well as formation of solid copper hexacyanoferrate near the polymer surface. Accumulation of Cu2+ ions was found to be advantageous from the point of view of PEDOT(HCF) applications as a solid contact (ion-to-electron transducer) in all-solid-state Cu2+-selective electrodes with solvent polymeric polyvinyl chloride (PVC) based membrane, containing Cu2+-selective ionophore. Binding of Cu2+ ions in the conducting polymer layer results in analyte ions flux into the transducer phase. Thus, pronounced enhancement of selectivity of the all-solid-state Cu2+-selective electrode or lower detection limit of the potentiometric response range was achieved, reaching under optimised conditions 10−7 M CuSO4. [Copyright &y& Elsevier]

All-solid-state ion-selective electrodes that use a conducting polymer as the ion-to-electron transducer have emerged as one of the most promising classes of all-solid-state potentiometric sensors in recent years. This is largely because it has many analytical advantages, including high response stability, which is unique in the field of internal-solution-free ion-selective electrodes. This paper reviews the considerable progress that has been made in this area of sensing in recent years, in terms of detection limits, selectivity coefficients and novel construction methods. [ABSTRACT FROM AUTHOR]

Conducting polymer (CP) films, used as ion-sensing membranes under open circuit potentiometric conditions, are usually characterised with rather high detection limit, in the range of 10−4–10−5 mol dm−3. This effect is unfavourable, not only from the point of view of CP applications in potentiometry as ion sensitive membranes, but also when these materials are used as ion-to-electron transducers (solid contacts) for ion-selective electrodes. The theoretical considerations presented underline the crucial role of spontaneous processes of polymer charging/discharging—the source of observed high detection limit of sensors comprising CP layer under zero current conditions. Although the mechanism of occurring process is different from that observed for plastic, solvent polymeric based ion-selective electrodes, the ultimate result—alteration of activity of electrolyte at the membrane/solution interface leading to elevation of the detection limit—is the same.The method of estimation of parameters characterising spontaneous charge transfer processes is presented. The values obtained can be used to calculate the resulting polymer/solution interface activity of electrolyte ions, thus the detection limit of CP membrane can be theoretically predicted.A method of lowering of the detection limit of conducting polymer membranes, applying galvanostatic polarisation to compensate the spontaneous process of polymer charging/discharging, is presented.The experimental results obtained for poly(pyrrole), poly(N-methylpyrrole) and poly(3,4-ethylenedioxythiophene) are in good accordance with predictions of the presented model. [Copyright &y& Elsevier]

Two alternative simple and templateless procedures for synthesis of polypyrrole nanoparticles are described, with oxidation of pyrrole monomer either by iron(III) toluenesulfonate or potassium hexacyanoferrate(III), in presence of either alternating polymers micelles or poly(vinyl alcohol) as only dispersing medium. As confirmed by TEM pictures nanoparticles of uniform size close to 60 nm were obtained. Electrochemical properties of obtained nanoparticles, drop cast to form films on electrodes were studied using different techniques. It was shown that these layers were characterized by high electroactivity, fast ion exchange and almost capacitive properties in the oxidized state. These properties result from loosely packed structure of hydrophilic nanoparticles in the layer, surrounded by electrolyte solution. Although typically relatively immobile doping anions were used, they were easily released from the polymer assuring anion-exchange properties. The simplicity of the described synthesis procedures and high electroactivity of obtained nanoparticles is promising from the point of view of their possible applications. [Display omitted] [ABSTRACT FROM AUTHOR]

A novel approach is used for templateless synthesis of polypyrrole – gold nanocomposite material, taking advantage of polypyrrole nanoparticles synthesis method resulting in nanostructures of unblocked surface. Our approach leads to unsupported, nanocomposite system, where presence of gold nanostructures enables hydrogen ions reduction. Electrochemical methods: cyclic voltammetry, chronoamperometry or rotating disc electrode voltammetry allow to monitor the high rate of hydrogen ions transfer through the conductive polymer and their electrochemical reduction rate. These measurements confirm high active surface area of gold nanostructures immobilized in polypyrrole. On the other hand, electrochemical impedance spectroscopy reveals pseudocapacitive properties of the material, typical for polypyrrole nanostructures. Thus, the obtained nanocomposite material shows joint and unhindered properties typical for gold nanoparticles and polypyrrole nanospheres. Image 1085 [ABSTRACT FROM AUTHOR]

An experimental approach allowing visualization and quantification of the underestimated spontaneous process of partition of conducting polymer transducer material to the ion-selective membrane phase is proposed. The approach proposed is based on optical properties of the transducer material applied, using polythiophene as a model system. It is shown that this process occurs not only during the sensor preparation step but also during pretreatment of the sensor before use. As shown, this uncontrolled partition of the transducer to the receptor leads to conducting polymer contents in the membrane phase reaching 0.5% w/w; this process is accompanied by a partial spontaneous change of the oxidation state of polythiophene. The conducting polymer present in the membrane participates to some extent in the overall response of the sensor, which can be observed as a change in the polythiophene optical emission spectra. Fluorescence microscopic images obtained clearly show that the conducting polymer is distributed throughout the membrane thickness, being present also at the membrane/solution interface. The experimental results presented were obtained for K+-selective sensors using poly(3-octylthiophene) as a model transducer; however, the proposed approach is also applicable for other systems. [ABSTRACT FROM AUTHOR]

Abstract: Carboxy-functionalized graphene was used as a solid contact for potassium ion-selective electrodes with poly(vinyl chloride) based membrane. Transducer layers were obtained simply by application of a dispersion of graphene derivative in water. Analytical performance of thus obtained sensors was compared with that of all-solid-state sensors with typical transducer materials: poly(octylthiophene) applied as chloroform solution, conducting polymers available as aqueous dispersions of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) ions or polyaniline. It was found that all sensors tested were characterized with similar analytical parameters. Carboxy-functionalized graphene contact layer was in some respect similar to polyaniline one, what most probably results from the presence of pH sensitive groups in both materials. [Copyright &y& Elsevier]

Abstract: Polypyrrole microcapsules filled with different electrolytes were prepared using novel photopolymerization method. The obtained microstructurized material was applied as a transducer for ion-selective potentiometric sensors. In contrary to typical conducting polymer transducer, microcapsules result in introduction of significantly higher amount of exchangeable ions. Depending on the choice of electrolyte encapsulated, the resulting sensors were characterized with different analytical and electrical parameters. [ABSTRACT FROM AUTHOR]

A novel type of self-plasticizing polyacrylate-based membrane was developed for all-solid-state ion-selective potentiometric electrodes. The membrane composition contains a conducting polymer (CP): poly(3,4-ethylenedioxythiophene) end capped with methacrylate groups, chemically grafted with the membrane during the photo-polymerization step. This composition results in ion-selective membranes with the following advantages: lower electrical resistance compared to the CP-free membrane, facile ion-to-electron transduction between the membrane and the electrode support, controlled low activity of analyte ions, and high concentration of interferent ions (incorporated with the CP) within the membrane, potentially resulting in improved analytical parameters. Ca2+- and K+-selective membranes were chosen as model systems to study the effect of pretreatment and CP content on the potentiometric sensor's characteristics. For Ca2+ sensors, reproducible and stable Nernstian characteristics were obtained within the range from 0.1 to 10-9 M CaCl2, without a time-consuming preconditioning step. For K+-selective sensors, the influence on Nernstian response range was observed for varying KCl concentrations in the conditioning solution, with the lowest detection limit found close to 10-8 M KCl. Mass spectrometry coupled with laser ablation studies of the membranes revealed that in this case the detection limit is not related to primary ion content in the membrane contacting a sample solution, but is affected by interfering ion concentration close to the membrane surface. [ABSTRACT FROM AUTHOR]