A Simply Fabricated Neural Probe by Laser Machining of a Thermally Laminated Gold Thin Film on Transparent Cyclic Olefin Polymer

In this study, we propose a simple fabrication process of a neural probe based on the cyclic olefin polymer (COP). COP is a biocompatible material characterized by strong adhesion to gold and high UV transparency. Because of such adhesion, a gold thin film can be thermally laminated on a COP substrate using a heating press without an adhesion layer. In addition, the gold thin film can be micromachined by a UV laser without damaging the COP substrate, because the COP substrate has UV transparency. Compared with metal deposition and photolithography techniques used to fabricate conventional polymer-based neural probes, our process of fabricating a COP-based neural probe has no need of masks, vacuum, and fabrication facilities. A COP-based depth neural probe with a shank length of 10 mm was fabricated by the proposed process; this COP-based neural probe consists of four channels, each of which has a geometrical surface area of 100 × 100 μm (an average impedance magnitude of 14.8 ± 0.857 kΩ at 1 kHz). Based on multiple COP layers, the COP-based neural probe features adjustable elastic modulus (1.098–2.001 GPa). This elastic modulus was measured using buckling tests with varying thicknesses of 50, 100, and 200 μm. Furthermore, simultaneous multichannel neural signal recording was performed in vivo to assess the functionality of the COP-based neural probe. The results demonstrated the feasibility of the COP-based neural probe as a flexible depth neural probe with controllable stiffness.