A comparative study of conductive 3D printing filaments for electrochemical sensing applications pretreated by alumina polishing, electrochemical activa-tion, and electrodeposition of Au nanoparticles

3D printed electrochemical devices have gained tremendous attention recently because they are highly customizable platforms for analysis and energy storage that can be produced using simple, inexpensive components in a wide variety of settings. 3D printed electrochemical sensors, fabricat-ed from carbon-loaded conductive thermoplastics, enable decentralized production of electrochemi-cal devices that, if optimized, could be widely distributed. Achieving this goal requires a compre-hensive understanding of the electrochemical behavior of these filaments. Here, we investigated how the electrochemical behavior of three commercial filaments was affected by alumina polishing, electrochemical activa-tion in 0.5 M NaOH, and electrodepositing Au nanoparticles (NPs). Our goal was to understand if/how a selection of commercial filaments responds to these commonly used pretreatments rather than perform an exhaustive study of all possible combinations of filaments and pretreatments. We characterized the physical properties of each filament/pretreatment using thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and Raman microscopy measurements. We then benchmarked the background electrochemical processes (capacitance and solvent window) and the peak potential separation (∆Ep) of two common outer-sphere redox species (ruthenium hexamine and ferrocene methanol) for each filament under each pretreatment (i.e., nine total conditions). We subsequently investigated how the filaments responded to inner-sphere redox couples that were sur-face sensitive (ferrocyanide oxidation), dependent on surface adsorption (dopamine oxidation), and sensitive to surface oxides (Fe2+ oxidation). We found that the electrode form factor (i.e., size, ge-ometry, and contact method) matters tremendously when evaluating a 3D printable material’s elec-trochemical properties because uncompensated resistance can lead to misinterpretations of the HET kinetics using voltammetric methods. We also observed that the selected filaments do not respond to pre-treatments identically, and that detailed characterization (especially electrochemical character-ization, including non-faradaic background processes) must be employed when evaluating fila-ments. and electrodepositing metal nanoparticles is a very effective method of producing high-quality sensing interfaces regardless of filament and is probably underutilized in the field. Im-portantly, the latter insights were only possible by using a well-controlled form factor that behaved according to theory towards outer-sphere electron transfer couples.