Breath analysis is getting intensive attention as the importance of early diagnosis of diseases increases. A number of diseases such as halitosis, and diabetes can be diagnosed by detection of low concentration of biomarkers such as hydrogen sulfide, methyl mercaptan, dimethyl sulfide, and acetone in exhaled breath. As an attractive type of breath analyzing devices, a chemiresistive sensor which uses semiconductor metal oxide (SMOs) have been intensively studied. The SMOs-based sensing layers can provide tremendous advantages in terms of easy miniaturization, flexibility in production, simplicity of their use, and high connectivity with mobile devices. However, the SMOs have relatively low sensitivity and selectivity, which are challenge issues in practical use in application for exhaled sensors. The advances in nanostructures can address these issues, considering that the sensing reaction of analyte gases occur on the surface of the metal oxides. Tailoring of the SMOs nanostructures for large surface area and high porosity is a general approach for higher sensing performances. The catalytic functionalization is also inevitable process for high sensitivity and selectivity.
In this thesis, to develop the diverse three-dimensional (3D) hierarchical SMO nanostructure having large surface area as well as high porosity, the electrostatic spraying approach, and spray pyrolysis approach, which are facile and versatile technique, were adopted. Their sensing performances were investigated according to their morphological change and porosity. In addition, noble metallic nanoparticles (NPs) were functionalized on the SMO sensing layers to further improve sensitive and selective properties. Therefore, a number of sensing composites were prepared to establish sensor libraries. These sensor libraries were investigated to understand the sensing performances for breath pattern recognition using principal component analysis. This thesis demonstrated high potential feasibility of SMO-based sensing layer functionalized with diverse catalysts for application in breath analysis.