Iridium Oxide-Electrodeposited Nanoporous Gold Multielectrode Array with Enhanced Stimulus Efficacy.

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 ± 0.45 kΩ 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.

Electrochemical and in vitro neuronal recording characteristics of multi-electrode arrays surface-modified with electro-co-deposited gold-platinum nanoparticles.

In order to complement the high impedance electrical property of gold nanoparticles (Au NPs) we have performed electro-co-deposition of gold-platinum nanoparticles (Au-Pt NPs) onto the Au multi-electrode array (MEA) and modified the Au-Pt NPs surface with cell adhesive poly-D-lysine via thiol chemistry based covalent binding. The Au-Pt NPs were analyzed to have bimetallic nature not the mixture of Au NPs and Pt NPs by X-ray diffraction analysis and to have impedance value (4.0 × 10(4) Ω (at 1 kHz)) comparable to that of Pt NPs. The performance of Au-Pt NP-modified MEAs was also checked in relation to neuronal signal recording. The noise level in Au-Pt NP-modified MEAs was lower than in that of Au NP-modified MEA.

Performance assessments of vertically aligned carbon nanotubes multi-electrode arrays using Cath.a-differentiated (CAD) cells.

In this work, Cath.a-differentiated (CAD) cells were used in place of primary neuronal cells to assess the performance of vertically aligned carbon nanotubes (VACNTs) multi-electrode arrays (MEA). To fabricate high-performance MEA, VACNTs were directly grown on graphene/Pt electrodes via plasma enhanced chemical deposition technique. Here, graphene served as an intermediate layer lowering contact resistance between VACNTs and Pt electrode. In order to lower the electrode impedance and to enhance the cell adhesion, VACNTs-MEAs were treated with UV-ozone for 20 min. Impedance of VACNTs electrode at 1 kHz frequency exhibits a reasonable value (110 kΩ) for extracellular signal recording, and the signal to noise ratio the is good enough to measure low signal amplitude (15.7). Spontaneous firing events from CAD cells were successfully measured with VACNTs MEAs that were also found to be surprisingly robust toward the biological interactions.

Photopatterning of cell-adhesive-modified poly(ethyleneimine) for guided neuronal growth.

We describe photopatterning technique that employs the photodegradation of cell-adhesive-modified poly(ethyleneimine) (m-PEI) to fabricate precise micropatterns on the indium tin oxide (ITO) substrate for guided neuronal growth. The photodegradation of m-PEI coated on hydroxyl group-terminated ITO substrate created micropatterns over a large area through deep UV irradiation. The photopatterned m-PEI layer can effectively guide neurite outgrowth and control neurite extensions from individual neurons.

In vitro extracellular recording and stimulation performance of nanoporous gold-modified multi-electrode arrays.

OBJECTIVE: Nanoporous gold (Au) structures can reduce the impedance and enhance the charge injection capability of multi-electrode arrays (MEAs) used for interfacing neuronal networks. Even though there are various nanoporous Au preparation techniques, fabrication of MEA based on low-cost electro-codeposition of Ag:Au has not been performed. In this work, we have modified a Au MEA via the electro-codeposition of Ag:Au alloy, followed by the chemical etching of Ag, and report on the in vitro extracellular recording and stimulation performance of the nanoporous Au-modified MEA. APPROACH: Ag:Au alloy was electro-codeposited on a bilayer lift-off resist sputter-deposition passivated Au MEA followed by chemical etching of Ag to form a porous Au structure. MAIN RESULTS: The porous Au structure was analyzed by scanning electron microscopy and tunneling electron microscopy and found to have an interconnected nanoporous Au structure. The impedance value of the nanoporous Au-modified MEA is 15.4 ± 0.55 kΩ at 1 kHz, accompanied by the base noise V rms of 2.4 ± 0.3 µV. The charge injection limit of the nanoporous Au-modified electrode estimated from voltage transient measurement is approximately 1 mC cm(-2), which is comparable to roughened platinum and carbon nanotube electrodes. The charge injection capability of the nanoporous Au-modified MEA was confirmed by observing stimulus-induced spikes at above 0.2 V. The nanoporous Au-modified MEA showed mechanical durability upon ultrasonic treatment for up to an hour. SIGNIFICANCE: Electro-codeposition of Ag:Au alloy combined with chemical etching Ag is a low-cost process for fabricating nanoporous Au-modified MEA suitable for establishing the stimulus-response relationship of cultured neuronal networks.