A Novel Amperometric Transducer Electrode with Iridium‐Niobium Binary Alloys

Abstract

We have discovered that an Ir-23Nb binary alloy more effectively oxidizes hydrogen peroxide than Ir, Ir17Nb, or Nb. The oxidation capability was determined via cyclic voltammogram measurements of pH-buffer and hydrogen peroxide. We ascertained that applying a 0.7 V potential produces hydrogen peroxide currents of 9.2 mA/mm 2 Ir-23Nb, 5.3 mA/mm 2 Ir, 5.1 mA/mm 2 Ir-17Nb, 3.7 mA/mm 2 Ir-13Nb, 2.0 mA/ mm 2 Ir-30Nb, 1.5 mA/mm 2 Ir-43Nb, 0.6 mA/mm 2 Ir-62Nb, and 0.13 mA/mm 2 Nb. These results indicate that the effective oxidation of Ir-23Nb for hydrogen peroxide might be due to its fcc þ L1 2 two-phase structure and that Ir-23Nb can be used as an amperometric transducer material. The use of iridium (Ir) as a material for amperometric electrodes, especially in biosensors, has been reported in several studies [1 -5]. Research results have also been reported on the use of other materials [6], including binary alloys [7], for this purpose. However, using such materials is associated with inadequate hydrogen peroxide detection, susceptibility to interference species (e.g., ascorbic acid, uric acid, and acetaminophen), a high base current, and increased complexity in fabricating electrodes, among other problems [1 -5]. Hydrogen peroxide is produced by oxidases, and the interference species exist in body fluids. Adequate hydrogen peroxide detection and insusceptibility to interference species are needed in amperometric biosensors. Accordingly, Platinum has almost always been used in the materials of amperometric biosensor electrodes; carbon is an exception [8 -12]. Certain binary Ir alloys, i.e., Ir-Nb, IrZr, and Ir-Nb-Zr, have been noted as having high temperature materials [13,14]. However, the prices of rare metals including Ir have been fluctuating widely because of the global economic crisis and/or because they are mined in limited quantities. This has created a need to use alternative materials in place of Ir in various fields, including biosensor electrode fabrication. In our work, we found that an Ir-23 at.%Nb (Ir-23Nb) binary alloy can oxidize hydrogen peroxide better than any other Ir-Nb binary alloy. Figure 1 shows cyclic voltammograms of Ir (left graph) and Ir-23Nb (right graph). With pH-buffer cyclic voltammograms, the Ir oxidation current increased in the potential range from 0 to 0.2 V, reached a plateau between 0.2 and 0.75 V, and soared between 0.75 and 1.2 V. The Ir reduction current was roughly stable between 0 and À 0.3 V. In contrast, the Ir-23Nb oxidation current increased more than the Ir oxidation current from 0 to 0.25 V, decreased slightly between 0.25 and 0.5 V, and finally gradually increased more than the Ir oxidation current between 0.5 and 1.2 V. Like the Ir reduction current, the Ir-23Nb reduction current remained stable between 0 and À 0.3 V but increased more than the Ir reduction current after that. Due to pH-buffer reactions, increases in oxidation and reduction current occurred in a binary alloy having a 77Ir: 23Nb ratio or in one wherein a phase change from a singlephase fcc to...