Two-in-One Sensor Based on PV4D4-Coated TiO2 Films for Food Spoilage Detection and as a Breath Marker for Several Diseases

Abstract

Certain molecules act as biomarkers in exhaled breath or outgassing vapors of biological systems. Specifically, ammonia (NH3) can serve as a tracer for food spoilage as well as a breath marker for several diseases. H2 gas in the exhaled breath can be associated with gastric disorders. This initiates an increasing demand for small and reliable devices with high sensitivity capable of detecting such molecules. Metal-oxide gas sensors present an excellent tradeoff, e.g., compared to expensive and large gas chromatographs for this purpose. However, selective identification of NH3 at the parts-per-million (ppm) level as well as detection of multiple gases in gas mixtures with one sensor remain a challenge. In this work, a new two-in-one sensor for NH3 and H2 detection is presented, which provides stable, precise, and very selective properties for the tracking of these vapors at low concentrations. The fabricated 15 nm TiO2 gas sensors, which were annealed at 610 °C, formed two crystal phases, namely anatase and rutile, and afterwards were covered with a thin 25 nm PV4D4 polymer nanolayer via initiated chemical vapor deposition (iCVD) and showed precise NH3 response at room temperature and exclusive H2 detection at elevated operating temperatures. This enables new possibilities in application fields such as biomedical diagnosis, biosensors, and the development of non-invasive technology.

Influence of Silsesquioxane-Containing Ultra-Thin Polymer Films on Metal Oxide Gas Sensor Performance for the Tunable Detection of Biomarkers

“…The FTIR result of the deposited PV4D4 films is presented in Figure 2b. The as-deposited PV4D4 film (ring layer), represented by the orange line in Figure 2b, shows the characteristic band for the cyclotetrasiloxane rings, as also reported in previous studies [4,32]. Successful polymerization is indicated by the absence of bands above 3000 cm −1 , which represent the C-H stretching of sp 2 -hybridized carbon, i.e., vinyl groups.…”

“…The principle behind the hybrid gas sensors investigated in this study is similar to the one described in our previous work [4,32]. We coat MOX gas sensors with a polymer thin film to protect it from moisture and to tailor the selectivity of the gas sensor.…”

“…A non-invasive method is desired, allowing for a simple and cost-effective analysis of exhaled breath. As stated in various papers, at this time, noninvasive diagnostic methods such as gas chromatography/mass spectrometry (GC/MS) are considered to be the most accurate methods for obtaining a painlessly collected, extremely simple and non-invasive human breath sample [1,4].…”

“…H 2 , mainly because it is easily detected by MOX sensors, is a common target in this type of application and is being researched in the industry [10,[20][21][22][23][24][25][26][27]. Furthermore, it is associated with different types of gastric diseases mentioned in [4] and described in more detail in a previous work [28]. Recently, it has also been associated with the possible up regulation of neurotransmitters involved in appetite stimulation, leading to hunger suppression and weight loss [29].…”

“…In this work, we present a new addition to hybrid gas sensors, which were reported in previous studies [4,10,30], to increase their response to H 2 . A hybrid gas sensor consists of a MOX gas sensor coated with an ultrathin (~20-30 nm) polymer thin film on top of the sensor.…”