Flexible pH sensors based on printed nanocomposites of single-wall carbon nanotubes and Nafion

High-performance flexible pH sensors based on nanocomposites of single-wall carbon nanotubes (SWCNTs) and Nafion, fabricated by screen printing on flexible substrates in ambient air are demonstrated. The electrical characteristics and thus the sensing performance of the pH sensors monitoring the change in resistance of printed nanocomposite films in a wide range of pH from 1 to 12 were controlled by the number of printed layers in multi-patterns. The operational stability of the flexible pH sensors was nearly unchanged after 200 cycles of bending tests having a curvature radius of 5 mm, which is essential for intergration of flexible pH sensors into wearable nanoelectronics. The sensing mechanism of the chemiresistive pH sensors based on nanocomposites is investigated in terms of chemical reaction. The hydrogen or hydroxide ions in the pH solution interact with the carbonyl and C H bonds bonds of the nanocomposite film, which induces or withdraws positively charged carriers, respectively. In addition, a real-time pH sensor system integrated into a drone application with wireless communication and data transmitting modules is demonstrated for the simultaneous visualization of processed data and remote detection of targets on the user's smartphone based on a designed Android algorithm.