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Iridium Oxide–Electrodeposited Nanoporous Gold Multielectrode Array with Enhanced Stimulus Efficacy
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- Authors
- Yong Hee Kim, Gook Hwa Kim, Min Sun Kim, Sang-Don Jung
- Issue Date
- 2016-10
- Citation
- Nano Letters, v.16, no.11, pp.7163-7168
- ISSN
- 1530-6984
- Publisher
- American Chemical Society(ACS)
- Language
- English
- Type
- Journal Article
- Abstract
- A multielectrode array (MEA) was fabricated with electrodes consisting of iridium oxide (IrOx) electrochemically deposited on nanoporous gold (NPG) to improve the moderate charge injection limit (ca. 1 mC cm-2) of NPG MEA. IrOx was electrodeposited by performing cyclic voltammetry with an IrOx deposition solution. The IrOx was electrodeposited on Au (EIROF/Au) and on NPG (EIROF/NPG) MEA, and the samples were analyzed in terms of the charge injection limit, charge storage capacity (CSC), and electrochemical impedance. The charge injection limit of the EIROF(100-cycled)/NPG MEA was estimated to be 2.3 mC cm-2 by measuring the voltage transient, and this value is sufficiently greater than the neural damage threshold (ca. 1 mC cm-2) and is also comparable to that of sputtered IrOx films. Considering the low charge injection limit (<0.1 mC cm-2) for the EIROF(100-cycled)/Au MEA, the high charge injection limit for the EIROF/NPG MEA was explained to be a result of synergetic combination of the inherently large surface area of the NPG and electrically active EIROF. The EIROF(100-cycled)/NPG exhibited an impedance of 9.7 짹 0.45 k?? at 1 kHz and a CSC of 8 mC/cm-2, respectively, obtained via electrochemical impedance spectroscopy and integration of the cathodic current in a cyclic voltammogram. Scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy are used to conduct an elemental mapping analysis of the cross-sectional structure of the EIROF/NPG and revealed that the EIROF had been uniformly deposited on the surface of the interconnected Au. The efficacy of the improvement in the charge injection limit of the EIROF/NPG MEA was evaluated with rat hippocampal slices. The EIROF/NPG electrodes exhibited a steeper increase in the negative peak amplitude of the field excitatory postsynaptic potentials (fEPSPs), even with an electrical stimulation of a lower amplitude (1-4 V), prolonged negative fEPSPs wave after peak response, and decreased serial reduction of fEPSPs compared to NPG MEA, all of which strongly indicate an improved charge injection for the EIROF/NPG MEA over NPG MEA.
- KSP Keywords
- Cathodic current, Charge storage capacity, Cross-sectional structure, Cyclic voltammetry, Cyclic voltammogram, Damage threshold, Electrical stimulation, Electrically active, Electrochemical Impedance Spectroscopy, Electron microscopy(SEM), Elemental mapping