| AVS 66th International Symposium & Exhibition | |
| Thin Films Division | Wednesday Sessions |
| Session TF2-WeM |
| Session: | Thin Film Late News Session |
| Presenter: | Tomi Ryynänen, Tampere University, Finland |
| Authors: | T. Ryynänen, Tampere University, Finland R. Mzezewa, Tampere University E. Meriläinen, Tampere University T. Hyvärinen, Tampere University J. Lekkala, Tampere University S. Narkilahti, Tampere University P. Kallio, Tampere University |
| Correspondent: | Click to Email |
Microelectrode arrays (MEAs) are a common measurement platform in various biological in vitro studies where neuronal cells or cardiomyocytes are applied e.g. for drug screening, toxicity testing, cell model development or simply for increasing understanding of cell behavior. The field potential or impedimetric measurements, or stimulation performed with MEA are usually complemented with fluorescence imaging or microscopic inspection while or after the MEA recordings. The use of an inverted microscope is preferred, as imaging from the top side is often impossible because of the cell culturing medium and its reservoir placed on top of the MEA. With the inverted microscope there exists, however, another challenge. Typically, the tracks and the electrodes of the MEA are opaque and thus they prevent the full visibility of the cells from the bottom side. Partial solution is to make the tracks from transparent indium tin oxide (ITO) material. However, ITO electrodes are rare, simply because of their relatively high impedance and noise level. Instead, opaque low impedance Pt black or titanium nitride (TiN) electrodes are usually used with ITO tracks. Transparent low impedance graphene or conducting polymer electrodes have been demonstrated, but usually with challenges related to the ease of fabrication and stability. A recent approach is to use a very thin TiN layer made by atomic layer deposition (ALD) [1] or reactive sputtering [2] in the electrodes. The idea is to take benefit from TiN’s columnar structure and thus capability of decreasing impedance, but still maintain the transparency, at least to some extent.
In this study, we show that ion beam assisted electron beam deposition (IBAD) is a valid alternative for sputtering and ALD in depositing both transparent ITO tracks and very thin transparent TiN layers for the MEA electrodes. We evaluate the performance of different combinations of ITO tracks and ITO or TiN electrodes, both from imaging and impedance point of view. In the first version, both tracks and electrodes were made of ITO to guarantee full transparency and thus optimal imaging capability. In the 2nd version, ITO electrodes were coated with thin TiN layer to decrease impedance but still maintain (partial) transparency. In the third version the measurement capability was optimized by thick opaque TiN electrodes. The optical transmission and electrical impedance of these three versions were characterized and the biocompatibility of the MEAs was verified by cell experiments with human embryonic stem cell-derived (hESC) neuronal cells.
[1] Ryynänen et al. doi: 10.3389/fnins.2019.00226
[2] Mierzejewski et al. doi: 10.3389/conf.fncel.2018.38.00027