Reactive oxygen plasma treatment of 3D-printed carbon electrodes towards high-performance electrochemical sensors

Abstract Conductive 3D-printed platforms have been recognized an emerging class of materials with great potential to electrochemistry. However, such 3D-printed electrodes require a surface treatment to remove excess of polymer that hinders the electron transfer. We report a fast (2-min) and chemical-free protocol for the surface treatment of 3D-printed conductive electrodes based on reactive cold oxygen plasma. A dramatic improvement of electrochemical activity of 3D-printed carbon black-polylactic acid (CB-PLA) electrodes was verified by the decrease in the peak-to-peak separation of the voltammetric response for the [Fe(CN)6]3-/[Fe(CN)6]4- couple and in the resistance of change transfer. The O2-plasma treatment increased oxide groups and graphitic groups at the CB-PLA surface (verified by XPS) and provided higher rugosity (SEM images) thus higher exposure of conducting carbon sites and increased electroactive area in comparison with CO2-plasma, which explains the improved electrochemical performance using O2-plasma treated electrodes. This protocol is faster and provided improved electrochemical activity compared with electrochemical, chemical, or biological treatments. As proofs-of concept, the benefits of surface plasma treatment of the 3D-printed electrodes were demonstrated towards the electrochemical sensing of dopamine and nitrite, molecules of biological interest, including the analysis of human saliva. Values of sensitivity and detection limit were greatly improved when using O2-plasma treatment for both molecules (up to 100-fold increase in sensitivity for the voltammetric detection of dopamine), suggesting great promises for the development of highly-sensitive electrochemical sensors.