A tassel-type multilayer flexible probe for invasive neural recording

Invasive neural probes are one of the most critical components in the intracortical neural signal recording system. However, they can cause brain damage and tissue response during and after implantation. Thus, neural probes with high flexibility, biocompatibility, and simple implantation methods are required in brain research. Here we present a novel approach to fabricating a multilayer flexible tassel-type neural probe using low-cost maskless laser direct-write lithography, combined with straightforward release and assembly methods to prepare a whole implantation system. The probe has 32 recording electrodes with an area of 8 × 8 µm², arranged into two rows of different depths and 16 separated shanks, aiming at the neural signal recording in an extensive range. Polyimide and gold are used as the insulating and conductive layers, respectively. With the help of a polyethylene glycol (PEG) coating, the tassel structure was mechanically enhanced for successful implantation, and our morphology characterization showed that the diameter of the coated probe was less than 50 µm. Mechanical property tests also proved that it had the necessary stiffness for brain implantation. Afterwards, electrochemical tests were carried out, which showed that the probe had a rather low impedance after a simple gold electroplating. Finally, in vivo experiments demonstrated our probe can be successfully used in neural recording.