Inkjet printing and surface treatment of an optimized polyurethane-based ink formulation as a suitable insulator over silver for contact with aqueous-based fluids in low-voltage applications

An optimized, formulated polyurethane (PU)-based insulating ink, which was inkjet printed and cured as a tri-layer on top of an inkjet-printed and sintered commercial silver ink base metal fused to polyethylene terephthalate substrate, demonstrated a resistivity of >1.2 × 10⁸ Ω cm at a film thickness of 100 μm when exposed to an aqueous saline solution and a voltage differential of <2 V. This insulating property is highly desirable for biofluids-contacting biosensors. Three PU-based insulator ink formulations were made with different levels of ethylene glycol and carboxymethylcellulose additives to improve ink volatility, viscosity, and dispersion properties. Based on the resultant ink properties important to printing, one of these formulations was selected for further evaluation. The effects of the type and extent of surface conditioning involving UV–O₃ and/or thermal treatments on print quality and completed insulator functionality are discussed. Print quality is assessed by visual and profilometry measurement.