Handling electric connections in 3D-printed electrodes and sensors. Part I. Understanding and improving tracks and contacts

Voltammetric and amperometric sensors typically consist of three sections: an electroactive surface, an electrode substrate, and connection tracks or wires to a potentiostat or other electronic circuit. While the electrical resistance of metal-to-metal connectors can usually be disregarded in such sensors due to their low contact resistance, this is not the case when semiconductor materials, conductive polymers, or composites are involved. This study focuses on the electrical behavior of 3D-printed conductive polymer tracks and connections to metals, aiming to improve and understand their limitations. Carbon black PLA (CB-PLA) was chosen for its favorable electrical properties. Results show that the printed tracks exhibit higher resistivity (17 Ω·cm) than the raw filament (6 Ω·cm). The electrical contact resistance (ECR) found between nickel-plated metals and CB-PLA was considerably high, in the order of 10 ² to 10 ³ Ω. The metal-polymer contact promoted solely by pressuring the parts (e.g., with alligator clips) proved to be unstable and, as such, a potential source of noise. Welded metalpolymer contact (WMPC) was developed using induction heating to improve and secure metal-polymer interfaces. Furthermore, it has been demonstrated that the high resistivity of the tracks and connections created by 3D printing actually has no implication on the electrochemical behavior of the sensor, other than the Ohmic drop in these sections that must be considered to ensure the proper functioning of sensors involving current flow. The findings indicate that while 3D-printed conductive polymer sensors show promise for widespread use, careful consideration of ECR and thermal effects is crucial for reliable performance.