Studies have shown that when an individual with diabetes has low insulin levels, the body is unable to burn glucose and converts those molecules into ketones, predominantly acetone. That acetone then transfers into the blood stream before being exhaled by an individual’s breath. Rather than using current methods to monitor diabetes, such as a blood test conducted by a finger prick, some researchers have suggested measuring the acetone in exhaled breath as a noninvasive method to monitor diabetes [1].

This noninvasive diabetes monitoring method is made possible by using resistive sensors that utilize a thin-film deposited on interdigitated electrodes. While healthy individuals will exhale 300-900ppb acetone, individuals suffering from diabetes may exhale up to 1800ppb acetone [2]. Recent studies have shown an ability of these sensors to reach the sensitivity required to sense acetone in these diabetic cases. When the sensor is heated, the conductivity of the film increases and allows for the flow of electrons between digits of the sensor. When acetone is present, the acetone adsorbs onto the acetone-sensitive material causing a noticeable change in resistance. As the concentration of acetone increases, the amount of acetone adsorbed on the film increases, causing a change in resistance which allows researchers to correlate acetone concentration with a sensor resistance.

One acetone-sensitive material that researchers are studying is epsilon-phase tungsten trioxide. While other forms of tungsten trioxide, such as the gamma-phase, can also sense acetone, the specific structure and surface dipole of the epsilon-phase allows for a particular sensitivity to high dipole moment compounds such as acetone [2]. Unfortunately, this material is prohibitive to use, as the epsilon-phase tungsten trioxide is not the thermodynamically preferred structure at the operating temperature [1]. Some researchers have used dopants, such as silicon or chromium to stabilize the epsilon-phase. However, past research has shown that by using Reactive Spray Deposition Technology (RSDT), it is possible to directly deposit tungsten trioxide onto sensors and anneal the material to achieve the epsilon-phase [3]. Using these undoped epsilon-phase tungsten trioxide sensors, as seen in the scanning electron micrograph in Figure 1, we are able to achieve a sensitive and durable film which can be used to detect the concentrations of interest for diabetes monitoring. This work will examine the acetone sensitivity of the undoped epsilon-phase tungsten trioxide films developed using RSDT and compare them to other research.

References:

[1] L. Wang, A. Teleki, S.E. Pratsinis, P.I. Gouma. Chem. Mater. 20 (2008) 4794-4796.

[2] M. Righettoni, A. Tricoli, S.E. Pratsinis. Chem. Mater. 22 (2010) 3152-3157.

[3] R. Jain, Y. Wang, R. Maric. J. Nanotech. Smart Mater. 1 (2014) 1-7.