Polyaniline Supported Atomic Gold Electrode Toward Glucose Oxidation

Abstract

Gold is reported to have unique catalytic properties for oxidization of alcohols in alkaline media, and the catalytic ability is dependent on size of the gold, which enhancement in the catalytic activity is observed following reduction of the size [1]. As size of the gold reduced to atomic level, the property would vary depending on the number of atoms in a gold cluster [1, 2]. For instance, the alcohol oxidation catalytic activity is promoted when there is an even number of gold atoms in a cluster and demoted when the gold cluster contains odd number of atoms [1, 3]. Simulation results indicate that the HOMO-LUMO gap switches between conductor and semi-conductor when the atom number changes [2]. Deposition of atomic level gold clusters is realized by a cyclic atomic gold deposition process utilizing polyaniline (PANI) as the supporting substrate [1, 3]. In this study, PANI decorated with different numbers of gold atoms is prepared, and effect of the gold atom number in glucose oxidation is evaluated for application in glucose electrochemical sensor.Figure 1 shows the fabrication process of the PANI/Au electrode. The PANI was prepared by electropolymerization on a pretreated platinum electrode. The electrolyte was composed of 0.1 M aniline monomer in 2 M HBF4. Color of the surface of the Pt electrode changed from silver to blue after the polymerization process. Thereafter, KAuCl4 was used as source of the gold in the cyclic atomic gold deposition process. Figure 2 shows sequence of the cyclic atomic deposition process for gold. In one cycle of the deposition, one and only one gold ion was attracted to an amine group in the PANI, and the attracted gold ion was reduced to form a gold atom. After preparation of the PANI/Au N (N indicates the number of the deposition cycle conducted) electrode, glucose oxidase (GOD) was immobilized as an enzyme on the electrode surface by a comprehensive crosslinking method.Figure 3 shows cyclic voltammogram (CV) results of glucose oxidation on the PANI/Au2 electrode when the glucose concentration in a phosphate buffer solution (PBS) was varied from 0 to 20 mM. Anodic current generated from oxidation of the glucose was confirmed when the concentration was higher than 5 mM. In order to reveal effects of the gold atom number on oxidation of glucose, PANI/Au N electrodes with the N changed from 1 to 3 were prepared. In the CV scans, a scan rate of 50 mV/s and 10.0 mM glucose were used. Figure 4 shows the CV results when using the PANI/Au N electrode as the working electrode. Anodic current caused by oxidation of glucose was observed in all the three electrodes. The current response increased when the deposition cycle was increased from 1 to 2, and the PANI/Au3 produced current responses between those of the PANI/Au1 and PANI/Au2. This implies that the glucose oxidation is lowered when an odd number of gold atoms is deposited. [1] Alex P. Jonke, Mira Josowicz and Jiří Janata, J. Electrochem. Soc. 159 2012 40-43. [2] E. M. Fernandez, J. M. Soler, I. L. Garzon, L. C. Balbas, Phys. Rev. B 70 2004 165403. [3] J. Janata, T. Nakamoto, IEEJ Transaction 11 2016 261-267. Figure 1