Electropolymerization Conditions Research Articles

Amperometric Detection and Quantification of Nitrate Ions Using a Highly Sensitive Nanostructured Membrane Electrocodeposited Biosensor Array

AbstractIn the past few decades, there has been a steady rise in the release of nitrate (NO3−), a prominent water soluble contaminant associated with the increasing use of nitrate based fertilizers. In this study, we suggest the use of a highly sensitive, enzymatic biosensor capable of quantifying minute concentrations of nitrate. The disposable nitrate biosensor consists of a sensing element in the form of nitrate reductase which is immobilized within a conductive polymer matrix to generate a quantifiable amperometric response. In this work, nanoarrays of co‐immobilized nitrate reductase and poly(3,4‐ethylenedioxythiophene) (PEDOT), were grown using a template assisted electropolymerization route. The performance of the biosensor is a strong function of electropolymerization conditions and the morphology of the PEDOT nanostructures. The electropolymerized biosensor displays excellent specificity w.r.t other interfering ions as evidenced from the initial rate kinetics. With a response time of a few seconds, limit of detection (LOD) as low as 0.16 ppm and sensitivity of about 92 µA/mM , the one‐step electropolymerized nanostructured nitrate biosensor developed in this study shows improved performance compared to similar electrochemical sensors reported in literature. The PEDOT/nitrate reductase nanowire sensor developed in this work shows superior attributes compared to a flat 2D nitrate reductase‐co‐immobilized PEDOT film grown using similar electropolymerization conditions. This combined with easy and fast fabrication technique opens up exciting opportunities for developing high accuracy PEDOT based nanobiosensors for field testing of nitrate contaminants in the future.

Electrochemical Determination of Pyrogallol at Conducting Poly(3,4‐ethylenedioxythiophene) Film‐Modified Screen‐Printed Carbon Electrodes

AbstractThe electrochemical oxidation of pyrogallol at electrogenerated poly(3,4‐ethylenedioxythiophene) (PEDOT) film‐modified screen‐printed carbon electrodes (SPCE) was investigated. The voltammetric peak for the oxidation of pyrogallol in a pH 7 buffer solution at the modified electrode occurred at 0.13 V, much lower than the bare SPCE and preanodized SPCE. The experimental parameters, including electropolymerization conditions, solution pH values and applied potentials were optimized to improve the voltammetric responses. A linear calibration plot, based on flow‐injection amperometry, was obtained for 1–1000 µM pyrogallol, and a slope of 0.030 µA/µM was obtained. The detection limit (S/N=3) was 0.63 µM.

Phospholipid vesicles as soft templates for electropolymerization of nanostructured polypyrrole membranes with long range order

Unilamellar vesicles are for the first time used as soft-templates in the electropolymerization of polypyrrole membranes with nanoscale organization and mesoscale order. The dimensions of vesicles (∼100–1000 nm) used as templates and the electropolymerization conditions lead to the formation of highly organized polypyrrole shells (10–25 nm thick) that are contiguous through the bulk of the membrane. These membranes templated with phospholipid vesicles are referred to as ‘biotemplated’ membranes and the technique ‘biotemplating’ owing to phospholipid's role as the fundamental building block of all cell membranes. Biotemplated polypyrrole membranes demonstrate higher specific surface area and subsequently higher specific capacitance than planar polypyrrole membranes and other nanostructured polypyrrole membranes for sodium and lithium ion storage. The higher specific capacitance resulting from biotemplating is explained through a mechanistic interpretation of the redox process using the number of accessible redox sites at the polymer–electrolyte interface. A direct correlation between the accessible and total number of redox sites in the polymer and specific capacitance of the conducting polymer is developed to illustrate the 45% increase in specific capacitance of biotemplated polypyrrole membranes.

Conjugated polymers as robust carriers for controlled delivery of anti-inflammatory drugs

Conjugated polymers due to their reversible transition between the redox states are potentially able to immobilise and release ionic species. In this study, we have successfully developed a conducting polymer system based on poly(3,4-ethylenedioxythiophene) (PEDOT) for electrically triggered, local delivery of an ionic form of ibuprofen (IBU), a non-steroidal anti-inflammatory, and analgesic drug. It was shown that by changing the electropolymerisation conditions, the polymer matrix of specified IBU content can be synthesised. The electrochemical synthesis has been optimised to obtain the conducting matrix with the highest possible drug content. The process of electrically stimulated drug release has been extensively studied in terms of the dynamics of the controlled IBU release under varying conditions. The maximum concentration of the released IBU, 0.66 (±0.10) mM, was observed at the applied potential E = −0.5 V (vs. Ag/AgCl). It was demonstrated that the immobilisation-release procedure can be repeated several times making the PEDOT matrix promising materials for controlled drug release systems applied e.g. in neuroprosthetics.

Electrochemical sensor for levofloxacin based on molecularly imprinted polypyrrole–graphene–gold nanoparticles modified electrode

A novel strategy was developed for the construction of a highly sensitive levofloxacin (LEV) sensor based on molecularly imprinted polymer (MIP) incorporation with graphene–Au nanoparticles (G-AuNPs). In this sensor, G-AuNPs dramatically promoted the electrooxidation of LEV on electrode while molecularly imprinted polypyrrole of LEV served as the recognition element. The electropolymerization conditions, method of template removal, and effects of supporting electrolyte and incubation time were investigated. Under optimized conditions, the oxidation peak current increased linearly with the concentration of LEV in the range from 1.0 to 100μmolL−1 with a detection limit (S/N=3) of 0.53μmolL−1. The MIP/G-AuNPs-based sensor was useful for the determination of LEV with high sensitivity, excellent selectivity and good reproducibility.

Urea Amperometric Biosensors Based on Nanostructured Polypyrrole and Poly Ortho-Phenylenediamine

Urea Amperometric biosensor was obtained on the base of nanostructured polypyrrole (PPy) and poly ortho- phenylenediamine (POPDA). The optimal conditions for monomer electropolymerization were determined. The effect of supporting electrolyte and number of deposition cycles on the OPDA and Py electropolymerization were studied. It was proved that POPDA and PPy were affected by pH changes and responded to the ammonium, product of urease catalyzed reaction. SEM images of the modified Pt/PPy electrode were presented. The cycle voltammograms and chrono amperometric curves of Pt/POPDA/urease and Pt/PPy/urease electrodes were studied. A good linear relationship was observed for Pt/POPDA/urease electrode in a concentration range from 6.7 to 54 mMurea. For Pt/PPy/urease electrode the linear relation in the range from 0.02 to0.16 mMurea was determined. The entrapped carbon nanotubes (CNT) in PPy film and the bipolymer layers were prepared for construction of Pt/PPy/CNT/urease, Pt/POPDA/PPy/urease and Pt/PPy/POPDA/urease biosensors. Obviously, the addition of POPDA to the composition of the two biosensors (Pt/PPy/POPDA/urease and Pt/POPDA/PPy/urease) reduced their sensitivity to urea. Pt/РPy/CNT/urease and Pt/РPy/ urease biosensors were 173 and 138 times more sensitive to urea than biosensor without PPy (Pt/POPDA/urease biosensor). It was found, that the performance of Pt/PPy/CNT/urease electrode was the best from the five obtained biosensors: linear range of urea concentrations—from 0.02 to0.16 mM; sensitivity—15.22 μA/mM and detection limit— 0.005 mM urea.

Preparation of a miniaturised iodide ion selective sensor using polypyrrole and pencil lead: effect of double-coating, electropolymerisation time, and current density

AbstractPolypyrrole (PPy) is a conducting polymer which can be used for producing different ion-selective electrodes. An iodide-doped (PPy-iodide) was prepared electrochemically by anodic polymerisation of pyrrole in the presence of an iodide ion in an aqueous solution on the surface of a pencil lead. Polymerisation was investigated under galvanostatic conditions. The effects of electropolymerisation conditions on the characteristics of the potential response of the sensor were examined. Concentrations of pyrrole, iodide ions, and conditioning solution plus current density and the time of electropolymerisation were optimised in relation to the slope and linearity of calibration graphs. This electrode showed a Nernstian behaviour of 61.1 mV per decade for I− ion over a wide concentration range from 1.0 × 10−5 M to 1.0 × 10−1 M, with the limit of detection of 9.3 × 10−6 M. The response time of the electrode was from 3–5 s. The selectivity coefficients of the prepared sensors over a wide spectrum of interference anions were also evaluated, revealing that selectivity improves as a result of double-coating with PPy. A similar improvement was observed under lower current density and longer electropolymerisation time. This sensor was applied in the determination of iodide ions using titration potentiometry. This electrode can be used for the determination of iodide in drug preparations.

Electropolymerized Polytyramine Film for the Selective Determination of Uric Acid

Electropolymerized polytyramine film was proposed for determination of uric acid in the presence of ascorbic acid. The influence of electropolymerization conditions on performance of the polytyramine film was examined to obtain the optimal experimental parameters. The voltammetric results demonstrated that polytyramine film obtained at the optimized conditions allowed penetration of large amounts of uric acid while blocking the permeation of electroactive (ascorbic acid, cysteine and oxalic acid) and non-electroactive interferents (lactose, sucrose and urea) through film in PBS. Therefore, it has been claimed that the polymeric film could be used as uric acid-selective membrane over a broad range of interference.

Effect of electropolymerisation conditions on the permeability of polyphenol films deposited on a vitreous carbon electrode

Polymeric films were prepared from alkaline (NaOH) phenol aqueous solutions on a vitreous carbon (VC) electrode by potentiostatic or galvanostatic electro-oxidation. Permeation through such films was studied by rotating-disk electrode using the ferricyanide redox couple, and by cyclic voltammetry using phenate ions. The influence of the electropolymerisation controllable parameters such as NaOH and phenol concentrations, potential or current applied, electrosynthesis time, temperature and hydrodynamic conditions (electrode rotation+solution magnetic stirring) on the permeability of these polymeric films was examined. Conditions for the removal of phenol by electropolymerisation are discussed on the basis of the permeability of polyphenol films obtained by electrosynthesis. Permeable films were formed for a concentration of free hydroxyl anion larger of 0.1M. An increase of the temperature to 85°C favours the formation of highly permeable films, thus avoiding electrode fouling.

Surface-modified reusable gold electrode for detection of dissolved oxygen

The behavior of gold electrodes for the detection of dissolved oxygen was studied by the method of cyclic voltammetry in a phosphate-buffered solution with physiological pH. Surface modification with electropolymerized poly (o-phenylenediamine) film was performed to improve electrode antifouling properties. The voltammetric signature of oxygen was considered in terms of film electropolymerization conditions and post-deposition conditioning of the electrodes. The changes in the chemical structure of the poly (o-phenylenediamine) films as a result of these factors were confirmed by X-ray photoelectron spectroscopy analysis. Following long post-deposition conditioning in a phosphate-buffered solution, the modified electrodes exhibited stable voltammetric signatures in repeated tests and during storage as well as in the presence of a dense population of Escherichia coli (characterized by negligible metabolic activity) in the buffer. The results are indicative of the improved electrode antifouling properties.

Indigo carmine (IC) doped polypyrrole (PPy) as a free-standing polymer electrode for lithium secondary battery application

Flexible free-standing polypyrrole-indigo carmine (PPy-IC) films were designed as additive-free anode material for lithium secondary batteries and were produced via the electropolymerization method. The films are soft, lightweight, mechanically robust, and electrically conductive. The films display a cauliflower-like structure consisting of micron-scale spherical grains, which are related to dopant intercalation in the polymeric chains. The morphologies and electrochemical behaviour of the free-standing PPy-IC films were affected by the electropolymerization conditions. Electrochemical tests demonstrated that the discharge capacity and initial coulombic efficiency increased as the thickness of the films decreased. The PPy-IC films prepared at lower deposition time (30min) and lower deposition current density (0.4mAcm−2) exhibited higher discharge capacity (83mAhg−1 beyond 100cycles) in the voltage range of 0.01–3.0V. These free-standing films can be used as possible anode materials to satisfy the new market demand for flexible/bendable lithium polymer or polymer batteries that are suitable for roll-up displays, wearable devices, and implanted medical devices used in biological and biomedical systems.

Reactivity of Monolayer Chemical Vapor Deposited Graphene Imperfections Studied Using Scanning Electrochemical Microscopy

Imperfections that disrupt the sp(2) conjugation of graphene can alter its electrical, chemical, and mechanical properties. Here we report on the examination of monolayer chemical vapor deposited graphene imperfections using scanning electrochemical microscopy in the feedback mode. It was found that the sites with a large concentration of defects are approximately 1 order of magnitude more reactive, compared to more pristine graphene surfaces, toward electrochemical reactions. Furthermore, we successfully passivated the activity of graphene defects by carefully controlling the electropolymerization conditions of o-phenylenediamine. With further electropolymerization, a thin film of the polymer was formed, and it was found to be insulating in nature toward heterogeneous electron transfer processes. The use of spatially resolved scanning electrochemical microscopy for detecting the presence and the "healing" of defects on graphene provides a strategy for in situ characterization and control of this attractive surface, enabling optimization of its properties for application in electronics, sensing, and electrocatalysis.

Polymer-based tubular microbots: role of composition and preparation

The influence of the composition and electropolymerization conditions upon the propulsion of new template-prepared polymer-based bilayer microtubular microbots is described. The effects of different electropolymerized outer layers, including polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT), polyaniline (PANI), and of various inner catalytic metal surfaces (Ag, Pt, Au, Ni-Pt alloy), upon the movement of such bilayer microtubes are evaluated and compared. Electropolymerization conditions, such as the monomer concentration and medium (e.g. surfactant, electrolyte), have a profound effect upon the morphology and locomotion of the resulting microtubes. The most efficient propulsion is observed using PEDOT/Pt microbots that offer a record-breaking speed of over 1400 body lengths s(-1) at physiological temperature, which is the fastest relative speed reported to date for all artificial micro/nanomotors. An inner Pt-Ni alloy surface is shown useful for combining magnetic control and catalytic fuel decomposition within one layer, thus greatly simplifying the preparation of magnetically-guided microbots. Polymer-based microbots with an inner gold layer offer efficient biocatalytic propulsion in low peroxide level in connection to an immobilized catalase enzyme. Metallic Au/Pt bilayer microbots can also be prepared electrochemically to offer high speed propulsion towards potential biomedical applications through functionalization of the outer gold surface. Such rational template preparation and systematic optimization of highly efficient microbots hold considerable promise for diverse practical applications.

Investigation of the anion uptake properties of cathodically electropolymerized poly(4-vinylpyridine) membranes

The cathodic electropolymerization conditions for poly(4-vinylpyridine) and the uptake characteristics of anions were evaluated with respect to their application to electrochemical sensing. The membranes were deposited from acidified acetonitrile solutions to minimize hydrogen gas evolution, which is prevalent in aqueous media at the applied potential range. Mid-infrared spectroscopic studies resulted in quantitative data relating the amount of monomer protonated with respect to the added acid, while 1H nuclear magnetic resonance spectroscopy provided insight into the resonance form preferentially adopted by the protonated monomer. The presence of defects in poly(4-VP) films was indirectly measured by monitoring the obstructed diffusion of cationic redox species through the film, and by correlating these electrochemical studies with mid-infrared spectroscopic analysis it became possible to determine the protonated-to-unprotonated monomer ratio yielding uniformly coated electrodes. Finally, the diffusion of Fe(CN)64− through poly(4-VP)-coated electrodes was evaluated as a function of pH, resulting in the conclusion that, unlike similarly deposited poly(2-VP) membranes, poly(4-VP) does not possess the loading capacity required for pre-concentration of anions.

Electropolymerization of chiral chromium–salen complexes: new materials for heterogeneous asymmetric catalysis

Electrochemical oxidation is described as a very efficient polymerization procedure for the heterogenization of metallic chiral catalysts. From chromium chiral complexes based on salen–thiophene ligands, this methodology provided an efficient access to various polymers. Recovered as insoluble powders, these materials were tested in different enantioselective heterogeneous catalytic reactions. Structural modifications were introduced on the salen core in order to evaluate their influence on redox polymer properties and on the enantioselectivity of the catalysis. Electrochemical experiments showed the particular stability of these deposited materials at the electrode surface and SEM analyses suggested the influence of the electropolymerization conditions on their morphology.

The effect of electrochemically polymerized pyrrole on the physicochemical properties and biological activity of carbon materials

Many of the vital processes in the human body are electrochemical in nature. Therefore, medical applications of electrochemistry show great promise. Particularly, detoxification by electrochemically controlled hemosorption combines biocompatibility of activated carbon with high adsorption activity toward toxic compounds. The present work involved the development of a controlled detoxification process using carbon adsorbents modified with polypyrrole. The electropolymerization of pyrrole on AG-3 activated carbon, which was initially quite aggressive towards erythrocytes, made it biocompatible. Glassy carbon and activated carbon were used to study the effect of polypyrrole on the physicochemical and biological activity of carbon materials. The magnitude and direction of open circuit potential shifts for these carbon materials depended on the conditions of electropolymerization. Adsorption activity of AG-3 activated carbon modified with polypyrrole was increased, as compared with untreated carbon.

Developing Polypyrrole-Based Oligonucleotide Biosensors

Many medical, forensic science, environmental and general scientific difficulties may be aided by the existence of suitable biosensors such as gene sensors, body fluid detection DNA sensors, disease detection DNA sensors etc. The sensor technology described here uses the conducting polymer polypyrrole (PPy) as both sensing element and transducer of sensing events. Stability and reproducibility are necessary characteristics of practical biosensors. The stability of polymers can be investigated using electrical impedance spectroscopy (EIS). This work discusses research focused towards creating a stable, reproducible sensor surface for oligonucleotide detection. The effect of electropolymerisation conditions (electropolymerisation method, solvent and electrolyte used), post-growth treatment (cycling and EIS experiments), and the sensing-environment conditions on sensor stability and applicability will be discussed.

Optimization of electrochemical polymerization parameters of polypyrrole on Mg–Al alloy (AZ91D) electrodes and corrosion performance

We report on the optimum electropolymerization conditions of polypyrrole (PPy) coatings on Mg alloy AZ91D electrodes from aqueous electrolytes of sodium salicylate via cyclic voltammetry (CV). Results show that initial and end potential values during the electrochemical coating procedure play an important role on the adhesion and corrosion performance of PPy films. Corrosion tests of AZ91D electrodes coated with PPy under optimized conditions show a good corrosion performance during 10 days in Na 2SO 4, without peeling off of these thin films.

Electropolymerization of phenol, o-nitrophenol and o-methoxyphenol on gold and carbon steel materials and their corrosion protection effects

This paper reports the results of a comparative study of the electropolymerization of phenol, o-methoxyphenol and o-nitrophenol by cyclic voltammetry on gold and carbon steel electrodes. The aim of this work is to synthesize homogeneous and adherent polyphenols film to protect carbon steel material against corrosion. Gold electrodes were used to optimize the experimental parameters such as the initial concentration of the monomer, the pH, the potential scan rate and the anodic potential limit value. Results showed that poly-o-metoxyphenol synthesized on carbon steel using optimized parameters obtained from gold electrode leads to more effective protection. This is probably due to the electron-donating mesomeric effet (+M) of the methoxy group which stabilized the phenoxy radicals obtained during the monoelectronic discharge of o-methoxyphenol. The best electropolymerization conditions involved an aqueous solution of 0.04M o-methoxyphenol at pH 10.7, 5mVs−1 potential scan rate and an anodic potential limit (1.64V/SCE) avoiding the degradation of the polymer film. The application of these conditions on steel electrodes leads to the formation of a stable, adherent and inhomogeneous film of polymer. A polymerization mechanism was proposed with consideration of results from literature.

Investigation of Near Ohmic Behavior for Poly(3,4-ethylenedioxythiophene): A Model Consistent with Systematic Variations in Polymerization Conditions

The impedance behavior of semiconducting polymer film electrodes based on poly(3,4-ethylenedioxythiophene) (PEDOT) in combination with a series of anionic dopants has been investigated using electrochemical impedance spectroscopy (EIS) over the frequency range from 0.1 Hz to 100 kHz. Films were electrodeposited on gold-coated Pt wire electrodes from a nonaqueous solution containing 3,4-ethylenedioxythiophene (EDOT). EIS results reveal that, under the optimal synthesis conditions, PEDOT electrodes consistently exhibit low, frequency-independent impedance over a wide frequency range (from ∼10 Hz to 100 kHz). These results suggest that the behavior originates from the two-layer homogeneous morphology of the film. A model for conduction in the films that is supported by experimental evidence is proposed, and EIS data for electrodes produced under a variety of electropolymerization conditions are presented.