Microelectrode Array With Transparent ALD TiN Electrodes

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.

Low impedance and highly transparent microelectrode arrays (MEA) for in vitro neuron electrical activity probing

“…As a comparison, a transparency of 84% was obtained for graphene/PEDOT:PSS-based MEAbut with higher surface impedance value of 117.3 ± 9.2 MΩ µm 2 at 1 kHz (30 μm diameter) [3] while an 80% transparency was obtained using ITO-based MEAs [26] with a surface impedance value of 1250 MΩ µm 2 (80 μm diameter) [9]. Table 1 and Fig.…”

“…Biocompatible, transparent microelectrodes have been demonstrated using a number of means. Thin titanium nitride (TiN) electrodes (30 µm in diameter) were fabricated by sputtering with an electrode surface impedance below 175 MΩ µm 2 [7] and a transmission at visible wavelengths of 50% [8]--or by atomic layer deposition (ALD) with an electrode surface impedance from 360 to 420 MΩ µm 2 and a transmission at visible wavelengths of 19-45% [9]. Due to the trade-off between metal transparency and metal conductance affecting optical transmission and electrode impedance (i.e.…”

Electrophysiological Analysis of Brain Organoids: Current Approaches and Advancements

“…Recent advances in bioprinting have been utilized to demonstrate proof-of-concept for patterning and printing MEAs on soft material substrates with mechanical properties similar to brain tissue, assisting with biocompatibility ( Adly et al, 2018 ; Borda et al, 2020 ). To improve electrode properties (i.e., biocompatibility, impedance, structural integrity, transparency), many new materials have been used for design and coating, such as indium tin oxide, gold, titanium nitride, and ruthenium oxide, among others ( Jahnke et al, 2019 ; Koklu et al, 2019 ; Ryynänen et al, 2019 , 2020 ; Atmaramani et al, 2020 ). The continued development of MEAs incorporating these and other materials, as well as improved incorporation methods, may help improve signal-to-noise ratios and fidelity for brain organoid recordings.…”

Electrophysiology Read-Out Tools for Brain-on-Chip Biotechnology

“…Nonetheless, one major drawback of these electrodes is their opacity, which makes simultaneous optical imaging difficult. Recent advances in materials have brought optically transparent electrodes, such as TiN-coated electrodes [ 206 ].…”