(Invited) Using Airbrushes to Pattern Reagents and Electrical Components on Flexible Substrates

Abstract

This paper is related to two subject areas. One subject area is point-of-care (POC) testing, which includes lateral flow assays that use paper as the substrate material to carry a sample toward the detection zone. The other subject area is flexible electronics, which could lead to wearable sensors and other devices. We report using airbrushes to pattern reagents and conductive inks onto a variety of flexible substrates including paper, thermoplastics, and elastomers. On paper substrates, we patterned small molecules, proteins, and DNA for sensing and biomarker detection. A range of operational parameters were used to control the line width and pattern contours. We employed an airbrush to pattern lines and dot arrays from hundreds of µm to tens of mm. Both enzymatic assays and DNA hybridization have been demonstrated in paper devices to show that the airbrushing method is amenable with various reagents and it has a potential to make paper-based devices more accessible. On both thermoplastics and elastomers, we explored the use of an airbrush to pattern electrical components and compare it with screen-printing. Among these substrates, elastomers such as polydimethylsiloxane (PDMS) are more stretchable than thermoplastics such as thermoplastic polyurethane (TPU). However, commercial conductive materials such as silver inks are not formulated to be adherent to PDMS. As a result, we developed a surface modification method to achieve better adhesion. We compared airbrushed resistors with screen-printed resistors and studied their adhesion and abrasion resistance. Changes in the resistance of resistors fabricated on both PDMS and TPU were investigated after they are stretched numerous times. Other electronic components and circuits have also been fabricated on flexible substrates.