Printed flexible electrochemical pH sensors based on CuO nanorods

Nanostructured metal oxides have attracted significant interest in a range of areas in electrochemical applications such as sensors, supercapacitors, and battery electrodes etc. Printing of these materials on flexible substrates will open new applications for the fabrication of sensors for monitoring the biological food -medicine-agricultural systems. This paper presents the printed CuO based flexible electrochemical pH sensors. The sensors with interdigitated electrodes, screen printed on flexible substrates, are based on CuO nanostructures having nanorods (NR) morphology. The morphology influences the charge transfer phenomena and hence the sensor performance, as confirmed by the electrochemical studies. The NR based sensors have better stability with respect to conventional nanoflowers (NF). The structural analysis shows NRs exhibit high crystallinity and low surface roughness (130 nm) with respect to NF (192 nm). The sensor capacitance in the test frequency range (20 Hz-10 MHz) decreases exponentially with increase in pH. The CuO NR based sensor exhibits a sensitivity of 0.64 mu F/pH in the range pH 5-8.5. The sensor performance towards interfrence to other ions and analytes such as Na+, K+, glucose, and urea was found to have negligible influence (+/- 1.5 nF) on the sensing electrode. The capacitance of sensors is also found to vary with different bending conditions. (C) 2018 Elsevier B.V. All rights reserved.