Self-cleaning ZnO/ITO/PET Bending Sensors

The design of multifunctional materials is of pivotal importance for developing wearable biosensors. In particular, the advancement in self-cleaning materials suitable for bending sensors, i.e. devices able to track human body movements for healthcare monitoring [1], has raised much interest in recent pandemic times. Such technology can be facilitated by leveraging piezo-photocatalytic cleaning effects under visible light [2]. Herein, we show a new class of ZnO-based nanosheets (NSs) synthesized in aqueous solution (85 °C, 24 hours) onto seeded or seedless ITO/PET surfaces that couple sensing to photocatalysis. UV-vis and FT-IR spectroscopies show the typical absorption peaks of ZnO. A nano-squared pattern is observed on ITO, likely resulting from mixed SnO2:ZnO nanocubic photocatalytic composites [3]. In the absence of the MnOOH seed layer film (seedless ZnO), NSs show flower-like morphology showing a significantly lower density (about twenty times) with respect to the seeded version. The electrical response of the sensors is extracted at a 1 V bias as a function of bending in the interval between 0° and 90°. The sensing response is dependent on the density of the ZnO NSs. Upon bending from 0° to 90°, the seedless ZnO sensors show 50-70 μA decrease, whereas the seeded ZnO sensors show a 180-200 μA decrease, which is about two times higher than the currently reported ZnO based bending sensors [4]. As a control, the bare ITO supports only show few μA decrease upon bending. The photocatalytic activity of the sensors is analysed in aqueous solution (methylene blue, 25 μM) at 1 Sun illumination. The seeded ZnO sensors show the best photocatalytic performances with respect to seedless ZnO and bare ITO. Upon bending the sensor inside the cuvette, the photocatalytic activities of bare ITO and seeded ZnO are improved (about 30%), whereas seedless ZnO is unaffected. After washing with deionized water, the sensors retain most of their photocatalytic activity. References [1] C. Chiappara, V. Campisciano, G. Arrabito, V. Errico, G. Saggio, G. Buscarino, M. Scopelliti, M. Gruttadauria, F. Giacalone, B. Pignataro, Bending Sensors Based on Thin Films of Semitransparent Bithiophene- Fulleropyrrolidine Bisadducts, ChemPlusChem 2020, 85, 2455. [2] S. C.Tu, Y.X. Guo, Y. H. Zhang, C. Hu, T. R. Zhang, T. Y. Ma, H. W. Huang, Piezocatalysis and Piezo- Photocatalysis: Catalysts Classification and Modification Strategy, Reaction Mechanism, and Practical Application. Adv. Funct. Mater. 2020, 30, 2005158. [3] R. Kumar, Ahmad Umar, Rajesh Kumar, M.S. Chauhan, Yas Al-Hadeethi, ZnO–SnO2 nanocubes for fluorescence sensing and dye degradation applications, Ceramics International, 2021, 47, 6201–6210. [4] M. Panth, B. Cook, M. Alamri, D. Ewing, A. Wilson, and J. Z. Wu, Flexible Zinc Oxide Nanowire Array/Graphene Nanohybrid for High-Sensitivity Strain Detection, ACS Omega 2020 5 (42), 27359-27367.