During the last few years, interest in wearable devices including a portable and wearable gas sensor system has increased. Since integration of fabric and gas sensors for a wearable breath monitoring system would allow continuous monitoring patients’ breathing gases such as acetone gas for diabetes (1), ammonia for renal disease (2), and ethanol for hepatic steatosis (3), realization of a miniaturized wearable gas sensor operating at daily environment is in demand.

Zinc oxide has definite advantages over other semiconducting nano-scale metal oxides because of its electric properties such as wide bandgap and high electron mobility (4). ZnO nanostructures have been investigated such as nanorods, nanotubes, and nanowires. Recently, hollow micro/nanosphere ZnO has been attracting attention. It may be able to apply for dye-sensitized solar cells, photocatalts, high performance electrodes, and gas sensors due to its large surface-to-volume ratio and reduced transport lengths for both mass and charge transport (5).

The researches about the catalytic decoration of ZnO gas sensors by metallic nanoparticles or layers have been also investigated to improve selectivity (6, 7). Especially, ZnO with silver is considered to exhibit relatively high sensitivity to ethanol (7). 

In this study, the hollow microsphere ZnO particles were prepared by a simple but new precipitation method and then Ag sputter coated. Electrophoretic deposition (EPD) of the hollow particles with Ag was then used to construct ZnO-Ag layers on flexible polyimide films. The structural properties of the deposited ZnO layers were analyzed by using SEM, TEM, and XRD.  Then, gas sensing behaviors to detect ethanol, acetone, and ammonia by thickness of Ag are discussed in detail.

This research was partially supported by the Korea Institute of Energy Technology Evaluation and Planning (20158520000210) grant funded by the Korea Government Ministry of Trade, Industry and Energy, a grant from a Strategic Research Project (2013-0132) funded by the Korea Institute of Construction Technology, and Auburn University IGP.

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(3) de Lacy Costello, B., Ewen, R., Ratcliffe, N. M., and Richards, M. (2008) J. Breath Res. 2, 037017

(4) Ahn, H., Park, J.-H., Kim, S.-B., Jee, S. H., Yoon, Y. S., and Kim, D.-J. (2010) Electrochemical and Solid-State Letters 13, J125-J128

(5) Xie, Q., Li, J., Tian, Q., and Shi, R. (2012) Journal of Materials Chemistry 22, 13541-13547

(6) Lupan, O., Chow, L., Ono, L. K. Ono, Cuenya, B. R., Chai, G., Khallaf, H., Park, S., and Schulte, A. (2010) The Journal of Physical Chemistry C 114, 12401-12408

(7) Lyashkov, A. Yu, Tonkoshkur, A. S., Aguilar-Martinez, J. A. and Glot, A. B. (2013) Ceramics International 39, 2323-2330