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3D structures & Nanocavities

While microelectrode arrays (MEAs) offer a range of advantages such as their non-invasive nature, the ability to interact with cellular networks over extended times and at multiple sites and excellent temporal resolution, they also exhibit the drawback of recording strongly attenuated signals. A possible approach for the improvement of the recording capabilities of MEA-based devices is to increase the cell-electrode contact via the introduction of additional dimensionality, either through protruding structures that enable phagocytosis-like events (3D structures) or via cavities allowing for cellular protrusion into the sensor (Nanocavities).

3D structures & Nanocavities_1



3D Structures

3D structures improve the cell-electrode coupling by inducing engulfment-like cellular behavior and thus increasing the cell-electrode contact. In our group, we investigate various different three-dimensional designs, e.g. cylindrical pillars, mushroom-like pillars with a cap, hollow pillars and hollow mushroom. We employ electron-beam lithography to define patterns that allow for the fabrication of metallic 3D structures via electrodeposition and have developed a process that enables the galvanic deposition of individual 3D nanoelectrodes. In this manner, we are able to produce 3D electrodes of multiple different designs and sizes on a single chip, allowing for parallel screening of various parameters and geometries for a direct comparison of the electrophysiological capabilities of the resulting nanostructures.

Since the formation of a tight cell-electrode contact is a prerequisite for a high sealing resistance and high signal amplitude, we aim to understand the geometrical conditions that facilitate a tight and stable interface. Employing HL 1 cells as model system, we utilize focused ion beam sectioning for the investigation of the interface between cell and electrode. By gathering information about the cellular response to the nanostructures, we can develop a better understanding of the design parameters necessary for better cell-chip coupling.


Nanocavities

Introducing cavities on microelectrode arrays poses one way to address shortcomings in standard planar MEA systems. Specfically, they exhibit decreased noise due to comparatively large sensor areas while maintaining the high spatial resolution of µm-scale electrodes. Furthermore, a high sealing resistance is formed by cells covering the electrodes, decreasing signal loss.
The nanocavites themselves are nanometer scale gaps between the microelectrode-array's (MEA) sensor material and its passivation layer.
A thin sacrificial chromium layer is evaporated on top of the gold or platiunum electrodes. This layer is only accessible through the electrode apertures. It is subsequently etched to produce the cavities.
Cultured cells adhering on the chip surface are suspended over the electrode openings, forming a tight seal.
With promising results obtained in electrochemical measurements, our work focuses on quantification, optimization and modification of the cell-cavity/electrode interface to achieve ideal signal coupling.


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