An iridium oxide nanoparticle and polythionine thin film based platform for sensitive Leishmania DNA detection

An impedimetric label-free genosensor for high sensitive DNA detection is developed. This system is based on a screen-printed carbon electrode modified with the thionine layer and iridium oxide nanoparticles (IrO₂ NP/). An aminated oligonucleotide probe is immobilized on the IrO₂ NP/polythionine modified electrode and ethanolamine was used as a blocking agent. Different diluted PCR amplified DNA samples have been detected. The selectivity and reproducibility of this system are studied and the system was highly reproducible with RSD ≈ 15% and sensitive enough while using 2% of ethanolamine during the blocking step employed for genosensor preparation

Poly(aniline) microelectrodes for ascorbate measurements

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Poly(aniline) microelectrodes for ascorbate measurements

The aim of this research was the production of a needle type microelectrode to monitor rapid changes of ascorbic acid, AA, in physiological fluids.  Poly(aniline), PANi, composites have been shown to be excellent electrocatalytic surfaces for the oxidation of NADH and AA.  Electrodeposition of PANi films on small platinum disc and elliptical microelectrodes was carried out under potentiodynamic and potentiostatic control.  The effect of the electrolyte and counter ion were studied in order to produce reproducible, stable and conducting PANi films.  Special attention was given to the final morphology of the resulting polymer film. Following previous work at Southampton University the incorporation of two poly(anions) was studied on a small scale: poly(vinylsulfonate), PVS, and poly(styrenesulfonate), PSS.  In addition alkylated and crosslinked PANi microelectrodes were investigated as an alternative to PANi composites to retain PANi conductivity at neutral pH.  The kinetic model proposed by Bartlett and Wallace on the RDE was compared with the data obtained at composite PANi microelectrodes.  It was found that the counter ion plays an important role during ascorbate oxidation.  The observed current responses to AA are half of the theoretical value for PANi-PSS microelectrodes.  A different reaction mechanism is proposed for PANi-PVS and PANi-PSS where an ascorbate radical anion intermediate might be present for the later composite.  The excellent electroanalytical properties shown by the modified PANi films were applied to real systems.  PANi-PSS microelectrodes were used as amperometric sensors for AA in low volume of human plasma. PANi-PVS elliptical needle type microelectrodes were successfully applied for the detection of ascorbate in the substomatal cavities of Barley leaves.</p

A comparison of rotating disc electrode, floating electrode technique and membrane electrode assembly measurements for catalyst testing

International audienceThe development of new catalysts for low temperature fuel cells requires accurate characterization techniques to evaluate their performance. As initially only small amounts of catalyst are available, preliminary screening must rely on suitable test methods. In this work, using a carbon supported platinum benchmark catalyst, the rotating disc electrode (RDE) technique was revisited in order to develop a detailed testing protocol leading to comparable results between different laboratories. The RDE results were validated by comparison with data measured both in proton exchange membrane single cells and via the relatively new floating electrode technique. This method can be operated with small amounts of catalyst but does not suffer from low limiting currents and allows prediction of high current capability of newly developed catalysts. Different durability testing protocols were tested with all three methods. Such protocols need to be able to introduce changes in the reference catalyst, but must not be too harsh as otherwise they cannot be applied to alloy catalysts. In all protocols an upper potential limit of 0.925 V was used, as this produced degradation in the chosen benchmark catalyst, but still represents realistic conditions for alloy catalysts

The Importance of Chemical Activation and the Effect of Low Operation Voltage on the Performance of Pt-alloy Fuel Cell Electrocatalysts

Pt-alloy (Pt-M) nanoparticles (NPs) with less expensive 3d transition metals (M = Ni, Cu, Co) supported on high surface area carbon supports, are currently the state-of-the-art (SoA) solution to reach the production phase in proton exchange membrane fuel cells (PEMFCs). However, while Pt-M electrocatalysts show promise in terms of increased activity for oxygen reduction reaction (ORR) and thus, cost reductions from a significantly lower use of expensive and rare Pt, key challenges in terms of synthesis, activation and stability remain to unlock their true potential. This work systematically tackles them with a combination of electrocatalyst synthesis and characterization methodologies including thin-film rotating disc electrodes (TF-RDE), an electrochemical flow cell linked to an inductively coupled plasma mass spectrometer (EFC-ICP-MS) and testing in 50 cm2 membrane electrode assemblies (MEAs). In the first part of the present work, we highlight the crucial importance of the chemical activation (de-alloying) step on the performance of Pt-M electrocatalysts in the MEA at high current densities (HCDs). In addition, we provide the scientific community a preliminary and facile method of distinguishing between a ‘poorly’ or ‘adequately’ de-alloyed (activated) Pt-alloy electrocatalyst using a much simpler and affordable TF-RDE methodology using the well-known CO-stripping. Since the transition metal cations can also be introduced in a PEMFC due to the degradation of the Pt-M NPs, the second part of the work focuses on presenting clear evidence on the direct impact of the lower voltage limit (LVL) on the stability of Pt-M electrocatalysts. The data suggests that in addition to intrinsic improvements in stability, significant improvements in the PEMFC lifetime can also be obtained via correct MEA design and applied limits of operation, namely restricting not just upper but equally important also lower operation voltage