Abstract
Cupric oxide (CuO) thin films are promising materials in gas sensor applications. The CuO-based gas sensors behaved as p-type semiconductors and can be used as part of an e-nose or smart sensor array for breath analysis. The authors present the investigation results on M-doped CuO-based (M = Ag, Au, Cr, Pd, Pt, Sb, Si) sensors working at various temperatures upon exposure to a low concentration of C3H8, which can be found in exhaled human breath, and it can be considered as a one of the biomarkers of several diseases. The films have been deposited in magnetron sputtering technology on low temperature cofired ceramics substrates. The results of the gas sensors’ response are also presented and discussed. The Cr:CuO-based structure, annealed at 400 °C for 4 h in air, showed the highest sensor response, of the order of 2.7 at an operation temperature of 250 °C. The response and recovery time(s) were 10 s and 24 s, respectively. The results show that the addition of M-dopants in the cupric oxide films effectively act as catalysts in propane sensors and improve the gas sensing properties. The films’ phase composition, microstructure and surface topography have been assessed by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) methods.
Highlights
Exhaled human breath is a complex mixture of inorganic gases (e.g., NO, CO2 and CO), volatile organic compounds (VOCs) and other typically non-organic volatile substances (e.g., N2) [1]
One of the VOCs that can be found in exhaled human breath is a propane C3H8
The presence of cooper and metal dopants was confirmed by energy dispersive X-ray spectroscopy (EDX)
Summary
Exhaled human breath is a complex mixture of inorganic gases (e.g., NO, CO2 and CO), volatile organic compounds (VOCs) (e.g., isoprene, acetone, propane) and other typically non-organic volatile substances (e.g., N2) [1]. Some of the VOCs are named “biomarkers”, since their presence in breath indicates disease. Breath analysis has many advantages over conventional laboratory tests. It is non-invasive and can be repeated frequently without any risk to the patient. Numerous studies, which appeared in the last few decades, correlate the presence of VOCs in breath to a certain disease, i.e., asthma [2], COPD (chronic obstructive pulmonary disease) [3], lung cancer [4], metabolic disorder [5], oxidative stress and others [6]. One of the VOCs that can be found in exhaled human breath is a propane C3H8
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