Luisa Pilan

Functionalized single-walled carbon nanotubes/polypyrrole composites for amperometric glucose biosensors.

This article reports an amperometric glucose biosensor based on a new type of nanocomposite of polypyrrole (PPY) with p-phenyl sulfonate-functionalized single-walled carbon nanotubes (SWCNTs-PhSO3−). An environmentally friendly functionalization procedure of the SWCNTs in the presence of substituted aniline and an oxidative species was adopted. The nanocomposite-modified electrode exhibited excellent electrocatalytic activities towards the reduction or oxidation of H2O2. This feature allowed us to use it as bioplatform on which glucose oxidase (GOx) was immobilized by entrapment in an electropolymerized PPY/SWCNTs-PhSO3− film for the construction of the glucose biosensor. The amperometric detection of glucose was assayed by applying a constant electrode potential value necessary to oxidize or reduce the enzymatically produced H2O2 with minimal interference from the possible coexisting electroactive compounds. With the introduction of a thin film of Prussian blue (PB) at the substrate electrode surface, the PPY/GOx/SWCNTs-PhSO3−/PB system shows synergy between the PB and functionalized SWCNTs which amplifies greatly the electrode sensitivity when operated at low potentials. The biosensor showed good analytical performances in terms of low detection (0.01 mM), high sensitivity (approximately 6 μA mM−1 cm−2), and wide linear range (0.02 to 6 mM). In addition, the effects of applied potential, the electroactive interference, and the stability of the biosensor were discussed. The facile procedure of immobilizing GOx used in the present work can promote the development of other oxidase-based biosensors which could have a practical application in clinical, food, and environmental analysis.

Supercapacitance of Single-Walled Carbon Nanotubes-Polypyrrole Composites

The composites based on carbon nanotubes (CNTs) and conducting polymers (CPs) are promising materials for supercapacitor devices due to their unique nanostructure that combines the large pseudocapacitance of the CPs with the fast charging/discharging double-layer capacitance and excellent mechanical properties of the CNTs. Here, we report a new electrochemical method to obtain polypyrrole (PPY)/single-walled carbon nanotube (SWCNT) composites. In the first step, the SWCNTs are covalently functionalized with monomeric units of pyrrole by esterification of acyl chloride functionalized SWCNTs and N-(6-hydroxyhexyl)pyrrole. In the second step, the PPY/SWCNTs composites are obtained by copolymerizing the pyrrole monomer with the pyrrole units grafted on SWCNTs surface using controlled potential electrolysis. The composites were further characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The results showed good electrochemical charge storage properties for the synthesized composites based on PPY and SWCNTs covalently functionalized with pyrrole units making them promising electrode materials for high power supercapacitors.

Electrochemical Activity and Corrosion Protection Properties of Doped Polypyrrole Electrodeposited at Pure Aluminium Electrode

ABSTRACT Polypyrrole films were electrodeposited at pure aluminium from aqueous solution of sodium sulphate containing pyrrole and organic compounds as dopants. Substrate-adherent polypyrrole films were obtained by electrochemical oxidation of pyrrole using the potentiodynamic method and cycling the electrode potential from 50 up to 100 cycles on the potential range of 0 ÷ 800 mV. Since the conducting polymers, such as polypyrrole, are electrosynthesized easily at inert electrodes such as gold and platinum, but much more difficult at aluminium electrodes, the surface protective oxide, Al2O3, was removed, as it acts as a barrier inhibiting electron transfer and the polymerization process. The electrochemical properties of polypyrrole films electrosynthesized from aqueous solutions containing sodium dodecylsulphate (SDS) and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) as doping electrolytes were studied by cyclic voltammetry and electrochemical impedance spectroscopy. The results indicate that the mechanism of the redox process is complex and may be governed by the diffusion of the electrolyte. The cyclic voltammograms of polypyrrole film synthesized in solutions having different concentrations of SDS and AOT indicate that the dopant concentration plays a very relevant role in the electrochemical response of the doped polypyrrole films like as: PPY/SDS/aluminium oxide and PPY/AOT/aluminium oxide. The results indicate that the SDS and AOT anions favor redox processes which are faster and more reversible than those associated to usual polypyrrole electrodes. However, the aluminium substrate had a considerable effect on the electrochemical activity of the polypyrrole films and that, because in the presence of pyrrole, anodization of these electrolytes resulted in formation of Al2O3 and PPY layers simultaneously. This is consistent with a galvanic interaction between the polymer and the aluminium substrate, giving rise to oxidation of the aluminium and reduction of the polymer. The corrosion performance of polypyrrole coated aluminium was evaluated by DC polarization and Electrochemical Impedance Spectroscopy. Our results show that the presence of polypyrrole coatings significantly increases the corrosion potential and drastically reduces the corrosion current and corrosion rate of pure aluminium. The corrosion resistance of polypyrrole coated aluminium was higher than of uncoated aluminium.

Carbon Substrate Functionalization with Diazonium Salts Toward Sensor Applications

Grafting of electroactive p-phenyldiazonium derivatives was performed on carbon electrodes. Reduction potentials were determined for commercial and new synthesized diazonium salts, in relation to the electronic behaviour of the para substituents of the diazophenyl groups. Their covalent attachment on the electrode surface was characterized through electrochemical experiments. The effect of varying several parameters (concentration, substituent, duration …) was investigated for potentiodynamic and potentiostatic grafting reactions. Spontaneous binding was identified by simply deeping the electrodes in diazonium salt solutions, affording low coverage (lower than 3%) and grafting densities of less than Γ = 3.9·10−11 mol·cm−2.

Electropolymerization Compounds Used for the Obtainment of Modified Electrodes and Electrochemical Biosensors

Modified electrodes were obtained from pyrrole and aniline on different substrates like: platinum, titanium, zinc or aluminium substrates by electropolymerization or by co-electropolymerization from synthesis solutions containing different ratio of monomers. Cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the electrochemical properties of the resulting modified electrodes. Further, an amperometric biosensor for glucose was prepared by immobilization of glucose-oxidase into a poly(o-phenylenediamine) film by simple one-step electropolymerization on platinum substrate. The rejection of interference species may be additionally increased by placing additional layers of Prussian Blue that ensured electrode operation at low potential values or of polypyrrole, respectively.

Modified Electrodes Type Doped Polypyrrole/Pure Titanium and their Electrochemical Characterization

Polypyrrole (PPY) films were electrodeposited at pure titanium from different aqueous solutions. The electropolymerization process was carried out by galvanostatic method. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical properties of electrodes. The results indicate that the surfactant anion favors redox processes which are faster and more reversible than those associated to usual polypyrrole electrodes. In fact, while in PPY films doped by conventional, small anions (e.g., Cl−), the charge compensation is assured by uptake of the anions during oxidation and the release of the same anions during reduction, in the PPY films prepared in the presence of large-anions salts (e.g., sodium dodecylsulphate-SDS), the charge compensation appears to involve incorporation of cations since the large anions are not easily released from the polymer matrix. An equivalent circuit was proposed to successfully fit EIS data and the significant contribution of pseudocapacitance from polypyrrole was thus identified. EIS measurements on Ti/PPY film electrodes were carried out in the supporting electrolyte depending on the following parameters: PPY-film thickness, supporting electrolyte concentration c, temperature T, and polarisation potential E.

Electropolymerization Mechanism and Electrochemical Behaviour of Poly(o-phenylenediamine) film Synthesized in the Presence and Absence of some Surfactants

O-Phenylenediamine was electropolymerized on copper electrodes by means potentiodynamic method. The electrochemical properties of poly(o-phenylene-diamine)films electrosynthesized from aqueous solutions containing different anions were studied by cyclic voltammetry and spectroscopy. The results indicate that the mechanism of the redox process is complex and may be governed by the diffusion of the cations and anions of the electrolyte. The kinetics of the processes can be monitored by changing the nature of the electrolyte and this may allow modulation of the electrical and optical properties of poly(o-phenylenediamine)(POPD)films.The polymer film consisted of more than two components. Among those, only one component was active in oxygen reduction, which was formed mainly in the earlier stage of the electropolymerization. It was suggested that the active polymeric component has a structural unit similar to the cyclic dimer(2,3-diaminophenazine). Finally, the electropolymerization mechanism for the formation of the active and inactive components has been proposed.

Versatile graphene biosensors for enhancing human cell therapy

Technological advances in engineering and cell biology stimulate novel approaches for medical treatment, in particular cell-based therapy. The first cell-based gene therapy against cancer was recently approved by the US Food and Drug Administration. Progress in cancer diagnosis includes a blood test detecting five cancer types. Numerous stem cell phase I/II clinical trials showing safety and efficacy will soon pursue qualifying criteria for advanced therapy medicinal products (ATMP), aspiring to join the first stem-cell therapy approved by the European Medicines Agency. Cell based therapy requires extensive preclinical characterisation of biomarkers indicating mechanisms of action crucial to the desired therapeutic effect. Quantitative analyses monitoring critical functions for the manufacture of optimal cell and tissue-based clinical products include successful potency assays for implementation. The challenge to achieve high quality measurement is increasingly met by progress in biosensor design. We adopt a cell therapy perspective to highlight recent examples of graphene-enhanced biointerfaces for measurement of biomarkers relevant to cancer treatment, diagnosis and tissue regeneration. Graphene based biosensor design problems can thwart their use for health care transformative point of care testing and real-time applications. We discuss concerns to be addressed and emerging solutions for establishing clinical grade biosensors to accelerate human cell therapy.

Electropolymerization Mechanism and Electrochemical Properties of Polypyrrole Film Doped with a Large Anion

Using the galvanostatic method the polypyrrole films doped with common low molecular weight inorganic anions and with the large surfactant anions were obtained. The electrochemical behaviour of polypyrrole films electrosynthesised in the presence of 1,2 dihydroxybenzenedisulfonic(3,5)acid disodium salt(1,2 DHBSAS)was investigated by cyclic voltammetry. The study has been focused on the evaluation of the effects of electrosynthesis conditions on the electroresponse of the PPY films as well as on the role of the nature of the electrolyte on the doping process and on the interface properties of the polymer electrode.The results indicate that the kinetics of the redox process are mainly governed by diffusion of the cations and anions of the supporting electrolyte(cycling electrolyte), while the large anions remain immobilized in the polymer structure. Therefore, the kinetics of the process can be monitored by changing the nature of the electrolyte and this may allow modulation of the electrical and optical properties of PPY/1,2 DHBSAS film.

Fabrication of Polyaniline/Carbon Nanotubes Composites Using Carbon Nanotubes Films Obtained by Electrophoretic Deposition

In this study, we report a facile electrochemical method to obtain polyaniline/single-wall carbon nanotubes (PANI/SWCNTs) composite electrodes by combining the electroreduction of diazonium salts and electropolymerization of conductive polymers. In a first step, the SWCNTs are covalently functionalized with diphenyl amine through the electrochemical reduction of the 4-aminodiphenylamine diazonium salt in order to provide anchors for the subsequent polymer electrodepostion. The aniline oxidation remains possible on this grafted layer and PANI can easily be deposited on the diphenyl amine-modified electrodes. The electrochemically deposited PANI/SWCNTs composites exhibit excellent electrochemical charge storage properties making them promising electrode materials for high power supercapacitors.