Hanna Elzanowska

Glucose detection based on electrochemically formed Ir oxide films

Abstract Ir oxide (IrOx) films, known to be nanoporous, electronically conducting and biocompatible, were formed anodically on polycrystalline Ir substrates in neutral solutions and were used to immobilize glucose oxidase (GOx) using two different methods. The resulting electrodes were found to generate H 2 O 2 in the presence of glucose and oxygen, yielding an excellent response to glucose (up to 70 mM) by the oxidation of H 2 O 2 in both stirred and non-stirred neutral solutions. It was found that, while the preferred method of immobilization involves the growth of IrOx films in a ca. 130–160 U ml −1 GOx solution, these electrodes displayed relatively large K ′ m values (up to 190 mM), reflecting restricted diffusion of glucose inside these films. The thicker the film on the electrode, the more stable the electrode response, especially to solution agitation, but the larger were the K ′ m values. SEM examination of these electrodes showed that GOx deposits in the form of small clusters, with the more stable response obtained when these clusters are more uniformly distributed. These amperometric IrOx/GOx glucose sensors were found to be free of interference from ascorbic acid, uric acid and paracetamol, at their physiological concentrations.

Electrochemical Characterization of Sol-Gel Formed Ir Metal Nanoparticles

“© The Electrochemical Society, Inc. 1999. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS). The archival version of this work was published in Electrochemical and Solid State Letters, 1999, Vol. 2(7).”

Complications associated with kinetic studies of hydrous Ir oxide films

The kinetics of the oxidation and reduction of electrochemically formed Ir oxide films have been examined as a function of the potential limits used, oxide film thickness, solution pH and the degree of reversible aging (diminished kinetics) of the oxide. It is shown first that the oxidation kinetics of the principal Ir(III) to Ir(IV) redox reaction are diminished in acidic solutions if the lower potential limit is set so as to include the kinetically slow process which occurs in the anodic cyclic voltammetric pre-peak, A0. Consistent with this, in alkaline solutions, little evidence for the prepeak is found, reversible aging does not occur and the kinetics do not depend significantly on the lower potential limit. Other results show that, if kinetic measurements are made employing a lower limit more positive than the A0 pre-peak and an upper potential limit below that required to generate Ir(V) and/or Ir(VI) states, the kinetics of the Ir(III)/Ir(IV) process are independent of film thickness in acidic solutions. If anodic steps are made to 1.25 V or more in acidic solutions, the Ir(V)/(VI) states generated can mediate and, hence, accelerate, the oxidation of Ir(III) to Ir(IV), as seen by the unusual shapes of the j/t transients.

Supercoiled and linear plasmid DNAs interactions with methylene blue

Slow accumulation of plasmids from their diluted, pg/mL solutions (pH 4.7) on a well defined glassy carbon (GC) electrode surface allowed for the formation of stable electrode layers consisting of two types of plasmid DNAs - pUC19 and pGEX-4T-2, in two forms - supercoiled circular (sc) and linear (lin). In the presence of methylene blue (MB), a typical redox indicator, the oxidation signals of nucleic acid bases are significantly enhanced. The interactions of the plasmids with MB are tested and used to distinguish between various types of plasmids. Instead of an MB reduction signal at ca. -0.2V vs. SCE, typically used to study MB interactions with DNAs, we have used the corresponding oxidation signal at ca. -0.2V, MB(I), as well as another oxidation signal at 1.05 V, MB(III). On a bare GC electrode, the MB(III) and MB(I) signals are proportional to each other, while in the presence of the plasmid DNAs the relations between MB(III) and MB(I) depend on the type of plasmid. The plots: MB(III)/MB(I) vs. [MB] and MB(I) potential shift vs. [MB] are used to distinguish between the supercoiled and linear forms of the pUC19 and pGEX-4T-2 plasmids.