A flexible WO₃-Based pH sensor array for 2-D pH monitoring using CPLoP technique

In this letter, we demonstrate an inkjet-printed WO₃-based pH sensor array using WO₃/Ag and Ag/AgCl as working and reference electrodes, respectively, on a flexible polyimide substrate. Pre-treated by Tollen's reagent, the printed Ag lines as sensor interconnects can exhibit a denser microstructure with lower electrical resistivity. As a result, the WO₃ nanoparticles can be well printed and sintered at 120 °C on the Ag lines as the working electrodes of the pH sensors. Experimental results show the sensitivity of the pH sensor to be as high as -24.4 mV/pH. The array comprising six pH sensors shows potential for real-time 2-D pH sensing applications.