Gook Hwa Kim

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.

Fabrication of multi-electrode array platforms for neuronal interfacing with bi-layer lift-off resist sputter deposition

We report a bi-layer lift-off resist (LOR) technique in combination with sputter deposition of silicon dioxide (SiO2) as a new passivation method in the fabrication of a multi-electrode array (MEA). Using the photo-insensitive LOR as a sacrificial bottom layer and the negative photoresist as a patterning top layer, and performing low-temperature sputter deposition of SiO2?followed by lift-off, we could successfully fabricate damage-free indium-tin oxide (ITO) and Au MEA. The bi-layer LOR sputter deposition processed Au MEA showed an impedance value of 6???105?? (at 1?kHz), with good consistency over 60 electrodes. The passivation performance of the bi-layer LOR sputter-deposited SiO2?was tested by electrodepositing Au nanoparticles (NPs) on the Au electrode, resulting in the well-confined and uniformly coated Au NPs. The bi-layer LOR sputter deposition processed ITO, Au, and Au NP-modified MEAs were evaluated and found to have a neuronal spike recording capability at a single unit level, confirming the validity of the bi-layer LOR sputter deposition as an effective passivation technique in fabrication of a MEA. These results suggest that the damage-free Au MEA fabricated with bi-layer LOR sputter deposition would be a viable platform for screening surface modification techniques that are available in neuronal interfacing.

Facile photopatterning of polyfluorene for patterned neuronal networks

In this paper, we demonstrated a facile photopatterning method that uses photocrosslinkable polyfluorene to fabricate micro-sized photopatterns on transparent indium tin oxide substrate for neuronal patterning. The modified poly(ethyleneimine) (m-PEI) with trimethoxysilane moiety was chemically attached to the hydroxyl group-terminated ITO surface and then the photopatternable polyfluorene derivative was spin coated as a cell-repellent layer onto the m-PEI-coated surface. The well-defined micropatterns were easily created over an entire surface by photocrosslinking of bromoalkyl-substituted polyfluorene (Br-PF) via the radical coupling reaction of a C–Br bond under UV irradiation without an initiator. UV-Vis absorbance, photoluminescence, ATR-FTIR and X-ray photoelectron spectroscopy were used to confirm the photocrosslinking process and the surface composition before and after the photocrosslinking of polyfluorene. The pairing of adhesive m-PEI and repulsive Br-PF effectively guided the neurite outgrowth and controlled neurite extension from individual neurons to the pre-patterned direction with excellent pattern fidelity. Guided neuronal cells were maintained for at least 25 days in vitro without any detachment of neuronal cells during cell culture. A photopatternable polyfluorene derivative in combination with cell-adhesive m-PEI is proved to be an effective way to modify the electrode surface to achieve single cell level neuronal networks.

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.

A high-performance transparent graphene/vertically aligned carbon nanotube (VACNT) hybrid electrode for neural interfacing

Neural interfaces that do not damage cells or tissues are key to connecting brain functions to neural prosthetics. Here, we designed a transparent graphene/vertically aligned carbon nanotube (VACNT) electrode capable of extracellularly recording spontaneous action potentials in Sprague–Dawley rat primary cortex neurons. Graphene provided the dual function of contacting the VACNTs and visually monitoring the cell viability. The hybrid electrodes exhibited remarkably high peak-to-peak signal amplitudes (1600 μV) and low noise levels, presumably due to tight junction formation between the cells and the deformed CNTs. Spike simulation and high-resolution transmission electron microscopy (HRTEM) imaging confirmed the excellent interfacial characteristics of the cells and the transparent hybrid electrodes.

Multi-electrode arrays modified with bimetallic nanoparticles; electrical performance and neural signal recording

Microelectrode for neural signal recording was modified with Au-Pt nanoparticles (NPs). Impedance of Au-Pt NP-modified electrode was decreased by one order of magnitude compared with bare gold electrode which results in decreasing baseline noise and higher signal to noise than those of the Au NP-modified MEA. The reasonable neuron cell viability and spike recording capability were observed on Au-Pt NPs- modified electrode.

Fabrication of gold multi-electrode array with bi-layer lift-off resist technique and surface modification with gold nanoparticles by electrochemical deposition

Electrochemical deposition of gold nanoparticles (Au NPs) on the gold multi-electrode array (MEA) fabricated with bi-layer lift-off resist sputter-deposition technique was performed. Electrochemical deposition was performed by potentiostatic and cyclic voltammetry method. The surface of Au NP-modified electrode showed various morphologies with applied voltage and the concentration of HAuCl4 solution. The Au NP-modified electrode was characterized by electrochemical impedance spectroscopy and cyclic voltammogram. The performance of Au NP-modified MEA was also tested by neuronal signal recording. The Au NP-modified MEA exhibited lower baseline noises and can record neuronal spike signals longer than the bare Au MEA.