Microelectrode Array With Transparent ALD TiN Electrodes.

Tomi Ryynänen,Oili M E Ylivaara,Jukka Lekkala,Jouni Ahopelto,Susanna Narkilahti,Anssi Pelkonen,Tanja Hyvärinen,Kestutis Grigoras,Mika Prunnila

doi:10.3389/fnins.2019.00226

Tomi Ryynänen, Oili M E Ylivaara + Show 7 more

Open Access

https://doi.org/10.3389/fnins.2019.00226

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Abstract

Low noise platinum black or sputtered titanium nitride (TiN) microelectrodes are typically used for recording electrical activity of neuronal or cardiac cell cultures. Opaque electrodes and tracks, however, hinder the visibility of the cells when imaged with inverted microscope, which is the standard method of imaging cells plated on microelectrode array (MEA). Even though transparent indium tin oxide (ITO) electrodes exist, they cannot compete in impedance and noise performance with above-mentioned opaque counterparts. In this work, we propose atomic layer deposition (ALD) as the method to deposit TiN electrodes and tracks which are thin enough (25–65 nm) to be transparent (transmission ∼18–45%), but still benefit from the columnar structure of TiN, which is the key element to decrease noise and impedance of the electrodes. For ALD TiN electrodes (diameter 30 μm) impedances from 510 to 590 kΩ were measured at 1 kHz, which is less than the impedance of bare ITO electrodes. Human induced pluripotent stem cell (hiPSC)-derived cortical neurons were cultured on the ALD TiN MEAs for 14 days without observing any biocompatibility issues, and spontaneous electrical activity of the neurons was recorded successfully. The results show that transparent ALD TiN film is a suitable electrode material for producing functional MEAs.

Highlights

The simplest and very popular method to perform in vitro electrophysiological measurements for neuronal and cardiac cells is to plate the cells on a microelectrode array (MEA)
We propose using atomic layer deposition (ALD) titanium nitride (TiN) electrodes as potential solution to fabricate transparent MEAs with lower impedance compared with indium tin oxide (ITO) electrodes
Transparency of the ALD TiN films deposited on glass substrates that were later processed as MEAs were measured with Ocean Optics JAZ spectrometer over wavelength range from 350 to 1000 nm

Summary

INTRODUCTION

The simplest and very popular method to perform in vitro electrophysiological measurements for neuronal and cardiac cells is to plate the cells on a microelectrode array (MEA). With MEAs this leads to another challenge – the opaque electrodes and tracks lie between the cells and the microscope optics, i.e., the cells or cellular processes located on the electrodes, which are often the most interesting points to observe, are not visible. To overcome this challenge MEAs with transparent indium tin oxide (ITO) electrodes and tracks have been used occasionally. We propose using ALD TiN electrodes as potential solution to fabricate transparent MEAs with lower impedance compared with ITO electrodes

MATERIALS AND METHODS

RESULTS

DISCUSSION