A silicon-based spiky probe providing improved cell accessibility during in vitro slice recordings

Abstract

AimsIn this study, we introduce an edge-type laminar silicon probe suitable for improved cell accessibility during in vitro brain slice recordings. With protruding contact sites, the spiky probe provides high signal yield and quality while approaching cells located deeper in the tissue. Methods. The spiky probe comprises an angled shank carrying 32 protruding contact sites with three possible spacing of 25 μm, 50 μm and 100 μm. The angled shank makes the probe compatible with large microscope objectives used typically in two-photon imaging, in vitro. Spiky probes were batch manufactured with high precision using the etching before grinding technology and bonded to a custom designed printed circuit board. A quantitative comparison of the performance was made against a commercially available surface probe. To investigate the long-term stability of contact sites, the spiky probe was repeatedly inserted in seven experiments (17 insertions, in total) using Wistar rat hippocampal slices, in vitro. Impedance magnitudes and phase angles were compared before and after the extensive usage. ResultsSingle unit activities were recorded with higher neuronal yield and higher amplitudes compared to the surface probe. Impedances did not increase significantly after reusing the probe in multiple experiments. Furthermore, we were able to detect extracellular action potentials from the same single unit on multiple, adjacent contact sites. Finally, we separated the recorded single units into putative cell types based on their extracellular waveforms. Conclusion and outlookThe spiky probes were proved to be optimal solutions to record extracellular spike waveforms, in vitro. The improved signal quality allowed us to distinguish between putative interneurons and principal cells. In future works, integrative experiments using these probes may provide multi-modal data for cellular electrophysiology resulting in a deeper understanding of single cell contributions to mass neural activity.