Hybrid Fabrication of an Electrochemical Electrode via Inkjet Printing on 3D-Printed Substrates

Combinations of additive manufacturing methods such as inkjet printing and various 3D printing techniques have led to advances in customizable electronic devices by reducing the need for the complex assembly of individually fabricated components. Such combinations are particularly attractive for the fabrication of electrochemical sensing platforms, where the sizes and spatial configurations of electrodes enable (or limit) the sensitivity of the sensors. However, to realize the potential of the combined fabrication methods, the parameters of each printing technique must be mutually compatible. For instance, electrochemical sensing assemblies consisting of inkjet-printed metals on 3D-printed plastics require post-processing steps that convert nanoparticular metals in precursor ink to conformal, mechanically stable, conductive films with negligible alteration to the underlying plastic substrate. While traditional sintering techniques convert inks to conductive metal films, the use of high temperatures are not compatible with structures printed via fused deposition modeling, for instance. In this proof-of-concept study, commercial gold inks were inkjet-printed onto 3D-printed poly-(lactic acid) (PLA) substrates. Optimization of the printing parameters and IR sintering resulted in stable, electrochemically active working electrodes. Surface characterization via scanning electron microscopy confirmed the formation of a homogeneous coating, and X-ray photoelectron spectroscopy data revealed the presence of gold on the surface. Electrical characterization via a four-point probe demonstrated a low sheet resistance, indicating the suitability of these electrodes for electrochemical measurements. Electrochemical data revealed that these gold electrodes are electrochemically active, and the diffusion-limited behavior of a redox probe was observed as expected. Additionally, these electrodes were tested for detecting lead in standard solutions, showing a linear response to lead concentrations, which indicates their potential in sensing applications. However, the detection range is significantly higher than the EPA-approved limit for lead concentrations in water, suggesting that electrode sensitivity requires further improvement. These findings have implications for fabricating inkjet-printed gold electrodes as sensors while highlighting the need for additional modifications to meet regulatory detection limits for heavy metal analysis.