Susana I. Córdoba de Torresi

Synthesis, characterization and immobilization of Prussian blue nanoparticles. A potential tool for biosensing devices

Prussian blue (PB) particles with the size of ca. 5 nm were synthesized and immobilized in a multilayer structure, as a strategy for the potential development of an amperometric transducer for oxidase-enzyme-based biosensors. Multilayer films composed of PB and poly(allylamine hydrochloride) (PAH) were prepared via layer-by-layer (LbL) sequential deposition. The process was carefully monitored by UV-vis spectroscopy and cyclic voltammetry. The increase of the redox current peaks during the layer-by-layer deposition demonstrated that charge propagation within the film occurs. Linear increase of UV-vis absorbance with the number of deposited bilayers indicates that well-organized systems have been elaborated. ITO electrodes coated with PB/PAH films were used successfully for detecting H2O2, sensitivity being dependent on the number of PB/PAH layers.

Polyaniline Based Acrylic Blends for Iron Corrosion Protection

Instituto de Qui´mica, Universidade de Sa˜o Paulo, 05513-970 Sa˜o Paulo, BrazilCoating strategies for corrosion protection considering intrinsically electronic conducting polymers have become important mainlybecause of restrictions on the use of heavy metals due to their environmental problems. This work presents the electrochemicalbehavior of an acrylic blend formed by sulfonate-doped polyaniline and poly~methyl methacrylate! used for corrosion protectionof iron in chloride solutions. The results would indicate that these blends have a dual protection mechanism; forming a passivatingcomplex with the dopant anion ~camphorsulfonate! and simultaneously acting as a physical barrier to avoid chloride anionpenetration.© 2001 The Electrochemical Society. @DOI: 10.1149/1.1381288# All rights reserved.Manuscript submitted October 28, 2000; revised manuscript received April 20, 2001. Available electronically June 15, 2001.

Polypyrrole/copper hexacyanoferrate hybrid as redox mediator for glucose biosensors

A copper containing Prussian Blue analogue was incorporated into a conducting polypyrrole film. The modified electrode was synthesized through an electrochemical two-step methodology leading to very stable and homogeneous hybrid films. These electrodes were proved to show excellent catalytic properties towards H(2)O(2) detection, with a performance higher than those observed for Prussian Blue and other analogues. Electrochemical impedance spectroscopy experiments demonstrated that the excellent performance of these hybrid films is strongly related to the electronic conductivity of the polymeric matrix that is wiring the copper hexacyanoferrate sites. A glucose biosensor was built-up by the immobilization of glucose oxidase; the sensitivity obtained being higher than other biosensors reported in the literature even in Na(+) containing electrolytes.

Optimized multilayer oxalate biosensor

The optimization of a biosensor prepared by the immobilization of oxalate oxidase (OOX) with a cross-linking agent onto a multilayer inorganic/organic modified electrode, is presented. A very thin Prussian Blue (PB) film covered by a self-doped polyaniline (SPAN) layer acts as very sensitive amperometric sensor for the H(2)O(2) formed by the enzymatic reaction. The electrode allows the very reliable and sensitive oxalate detection in the 0.08 to 0.45mmoll(-1) concentration range. The observed sensitivity was 131.3muAmmol(-1)cm(-2) at the operation potential of 0.05V versus Ag/AgCl in a succinate buffer solution (pH=3.8). The bilayer Prussian blue/SPAN leads to a very stable, sensitive and selective system that not only minimizes the interference caused by ascorbic and uric acids but also forms a very adherent sensing film that allows repetitive successive determinations.

Synthesis and characterization of stable Co and Cd doped nickel hydroxide nanoparticles for electrochemical applications

The present paper describes the physical-chemical characterization and electrochemical behavior of a new nanomaterial formed by the addition of cadmium and cobalt atoms into the structure of nickel hydroxide nanoparticles, these ones synthesized by an easy sonochemical method. Particles of about 5 nm diameter were obtained and characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction and Raman spectroscopy. Different nickel hydroxide nanoparticles were immobilized onto transparent conducting substrates by using electrostatic layer-by-layer providing thin films at the nanoscale and the electrochemical behavior was investigated. The formation of a mixed hydroxide was corroborated by observation of very interesting properties as redox potential shifting to less positive potentials and high stability when submitted to long electrochemical cycling or high times of ultrasonic synthesis, suggesting practical applications.

Mechanism of Action of Corrosion Protection Coating for AA2024-T3 Based on Poly(aniline)-Poly(methylmethacrylate) Blend

A corrosion protection coating for AA2024-T3 composed of a blend of camphorsulfonate-doped poly(aniline) (PANI) and poly(methylmethacrylate) (PMMA) is described. The open-circuit potential (OCP) for the bare and coated alloy in H 2 SO 4 solutions is presented vs. time. Raman spectroscopy revealed the oxidation state of the PANI component of the blend, both on undamaged films and as a function of distance away from a scratch on purposefully damaged films. The open-circuit and Raman data show galvanic coupling between the coating and the alloy, causing reduction of the PANI component. Scanning electrochemical microscopy was used to monitor H 2 evolution over a scratch on the surface of either PANI blend or PMMA films coated on AA2024. These experiments show that the scratched surface is highly active toward H 2 evolution when coated with only a PMMA film. In contrast, the blend coating drastically suppresses the amount of H 2 evolution in a scratch. This suppression of H 2 evolution was mimicked by poising the OCP of the PMMA-coated alloy at the same value at which it is poised by the PANI-containing film. It is shown that camphorsulfonate anion has no inhibitory effect on H 2 evolution in scratches on PMMA-coated AA2024.

Glucose Amperometric Biosensor Based on the Co-immobilization of Glucose Oxidase (GOx) and Ferrocene in Poly(pyrrole) Generated from Ethanol / Water Mixtures

The co-immobilization of GOx and ferrocene in a polymeric matrix by a one-step simple method is presented. This procedure to immobilize ferrocene as mediator implies the absence of modification of the monomer or the enzyme that would lead to the loss of its activity. Ferrocene incorporation results in an increase of sensitivity compared with the sensor prepared without the redox mediator (1.5 vs 0.23 mA mmol-1 L cm-2) and the decrease of the working potential to 0.4 V. The prepared sensor shows linear response till 10 mmol L-1 and response time of 2 s, in addition to reasonable stability after one week.

A New Sensor for Ammonia Determination Based on Polypyrrole Films Doped with Dodecylbenzenesulfonate (DBSA) Ions

Polypyrrole is the most widely used conducting polymer for sensors and biosensors construction once their conductivity and electroactivity do not strongly depend on the pH of the electrolyte. The aim of the present article is the improvement of amperometric ammonia determination, using dodecylbenzenesulfonate (DBSA) doped polypyrrole film. This large amphiphilic dopant promotes changes on the polymeric film leading to a more accentuated current and extending the linear response over a wide concentration range, when compared with films doped with small inorganic anions, such as chloride. The sensor×s response was followed by EQCM and Raman spectroscopy experiments with the aim of elucidating the mechanism of ammonia detection.

Chemical and electrochemical characterization of a novel nanocomposite formed from V2O5 and poly(N-propane sulfonic acid aniline), a self-doped polyaniline

Synthesis and characterization of new nanocomposites of V 2 O 5 and a sulfonated, alkylated polyaniline derivative [poly(N-propane sulfonic acid aniline), PSPAN] are described. Two types of PSPAN-V 2 O 5 nanocomposites have been produced, one by reaction of vanadium triisopropoxide solutions with N-propane sulfonic acid aniline and one by addition of H 2 O 2 to these same solutions. Nanocomposites are characterized using thermal gravimetric analysis, differencial scanning calorimetry (DSC), cyclic voltammetry, chronopotentiometry, and impedance spectroscopy. The increase of the 001 reflection spacing, X-ray diffraction results show that the polymer is intercalated into the V 2 O 5 interlayer region, consistent with the nanocomposite nature of the material. The DSC and infrared data suggest that water coordinated to vanadium sites exposed to the interlayer region is lost during formation of the nanocomposite. SEMs show that, in contrast to the relatively flat and featureless V 2 O 5 .1.6H 2 O thin films, the nanocomposites are highly textured and have quite small feature sizes. Electrochemical results show that some of the nanocomposites have larger specific capacity (307 Ah/kg) and faster reduction kinetics than V 2 O 5 .16.H 2 O and similar cyclability. The relevance of these results to general approaches to the production of nanocomposites for Li secondary battery cathodes is discussed.

Electrochemical and Raman studies on a hybrid organic–inorganic nanocomposite of vanadium oxide and a sulfonated polyaniline

The electrochemical and gravimetric behavior of a nanocomposite ([PSPAN]0.3V2O5·nH2O) comprised of poly(N-propane sulfonic acid aniline) (PSPAN) and vanadium pentoxide xerogel are described. Electrochemical quartz crystal microbalance (EQCM) measurements show that the charge compensation process in this nanocomposite occurs predominantly by Li+ transport with a small amount of accompanying solvent, especially at low scan rates. The diffusion coefficients for Li+ in both the vanadium pentoxide xerogel and in the nanocomposite are measured using the galvanostatic intermittent titration technique (GITT), and a value of 1×10−12 cm2 s−1 was determined for both materials. Combination of these results with electrochemical impedance spectroscopy (EIS) measurements shows that the nanocomposite is more electronic conductor and exhibits shorter ionic diffusion pathways than the vanadium pentoxide parent xerogel material. In situ Raman spectroscopic results on the nanocomposite unambiguously demonstrate the oxidation and reduction of the PSPAN component during redox cycling of the nanocomposite, even though the electrochemical signature of the PSPAN is obscured by that of the vanadium pentoxide component.