Influence of Degradable Substrates on the Performance of Screen-Printed pH Sensors

Sensor systems designed to degrade into non-toxic byproducts, after their operational lifespan, have attracted interest in recent years, particularly for single-use applications such as health monitoring, smart tickets and plant sciences. A wide variety of biodegradable substrates have been explored to develop such sensors using different functional materials. While the influence of functional materials on sensor performance has been well studied, the role of substrate material has not received much attention. The substrate related studies are limited to the evaluation of rate of degradation. Herein, we aim to evaluate the impact of substrates on the overall performance of the device. To this end, graphene-carbon (G-C) modified 1T-MoS2/carbon nanotube (CNT) based flexible pH sensors were screen printed on four biodegradable substrates namely Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), polyhydroxybutyrate (PHB), PHBV/Joncryl and cellulose acetate (CA) and their impedimetric measurements were recorded in the pH range of 2-6. It was observed that, for the same functional layer material i.e., 1T-MoS2/CNT, the pH sensors printed on CA substrate showed reliable results with sensitivity of 3.939 kΩ and correlation coefficient (R2) of 0.96. The sensors fabricated on other substrates failed to demonstrate stable and reliable output. The outcome shows the importance of substrate materials in determining the performance of degradable sensors and the crucial role they could play beyond supporting the active sensor layers.