Criticality of human breath detection with a portable device I: nanotechniques for improving sensing materials

Human breath is largely composed of oxygen, carbon dioxide, water vapor, nitric oxide, and numerous volatile organic compounds (VOCs) [1, 2]. Changes in the concentration of the molecules in VOCs could suggest various diseases or at least changes in the metabolism. Indeed, breath gases are recognized to be excellent indicators of the presence of diseases and clinical conditions. Such gases have been identified as biomarkers using accurate but expensive benchtop instrumentations such as gas chromatography (GC) or electronic nose (e-nose) [1]. As a consequence, in recent years, it has been stimulated the necessity to develop a portable device for breath analysis, easy to use, and feasible for patients living far from medical structures or physicians. In the framework of SEMEOTICONS (SEMEiotic Oriented Technology for Idividual's CardiOmetabolic risk self-assessmeNt and Self-monitoring) European Project, we developed a low cost, portable, easy-to- use device for the analysis of breath composition: the Wize Sniffer (WS). The first prototype of such device is based on commercial, semiconductor-based gas sensors. This type of sensors is very robust and easy to be integrated. Nevertheless, they are not selective, thus impeding the discrimination of each type of molecule they are able to detect. In this report we describe a method to improve the sensitivity of semiconductor-based gas sensors. In particular, we focus our attention on the development of a hybrid, ad-hoc sensor, based on Polyaniline sol- gel nano-film, to detect Nitric Oxide. Why Nitric Oxide? NOx (Nitrogen (di)Oxide) is a VOC that plays an important role as an indicator of metabolic since it is related to endothelial function [8]. In addition, it is a vasodilator and it modulates inflammatory response (operating in combination with CO and Hydrogen Sulfide). It is also a good indicator for asthma diseases. Detection of NO presents some challenging problems, because low cost sensors are not available. As a consequence, the development of a sensor for NO to be used in a portable device for breath analysis and taking advantage by nano-scale sensing materials imposed us to work harmonizing existing commercial sensors with innovative sensing materials.