A SU-8-based flexible microprobe for close and distal recordings from the cortical network

A 16-electrode flexible microprobe presenting an array of holes in its sensing area has been developed using SU-8 negative photoresist as a substrate material. The design of the microprobe consisted on six groups of 2-3 electrodes (50 μm in diameter and separated by 200 μm) placed in-between the array of holes. Distances between each group were appropriated for recording from a ferret slice, allowing us to evaluate the close versus the distant network activity. The holes were designed to allow the flow of oxygenated solution through the probe when measuring the neural activity of cortical slides maintained in vitro, while the gold electrodes have been modified with platinum black to decrease its impedance value and, therefore, improve the measurements. In particular, with this SU-8 microprobe it has been possible to register spontaneous slow oscillations and also induced activity in all 16 channels. The holes were useful to position puffers that allowed us to locally delivered drugs (glutamate) and to register its response. In addition, they were also used for sticking electrodes to simultaneously record single units that allowed us the synchronous recording of population activity (local field potential) with the electrodes of the probe and single unit activity (with glass or tungsten electrodes), demonstrating the feasibility of using SU-8 for the fabrication of neural microprobes as it can be customized to the required design.