Tailored synthesis and characterization of selective metabolite -detecting nanoprobes for handheld breath analysis
The abnormality in the concentration of certain trace gases in human breath, so-called biomarkers, could provide clues to diagnose corresponding diseases. For example, elevated isoprene is a result of cholesterol metabolic disorders, acetone is the biomarker of type-1 diabetes and NO is related to asthma. Non-invasive human breath analysis for disease diagnostics requires selective sensors that respond rapidly and with extreme sensitivity to specific biomarker gases.
On the other side, tungsten trioxide (WO3) is a very important semiconducting metal oxide which has shown great potential in gas sensing applications. WO3 exists in a series of stable solid phases at different temperatures from α phase to ϵ phase and an unstable hexagonal phase (h-WO3). However, except extensively studied y-WO3, the properties of other phases are still not fully known, esp. ϵ-WO3 and h-WO3 whose structures are different from other phases.
This dissertation discusses the development of several selective biomarker sensors based on room temperature (RT) stable ϵ-WO3 and h-WO3 nanostructured materials.
Ferroelectric ϵ-WO3 nanoparticles were synthesized using the flame spray pyrolysis method. Although the ϵ-WO3 polymorph vanishes during heat treatment in pure WO3 products, chromium dopants were utilized to stabilize this phase. The resistive sensor based on 10at%Cr doped ϵ-WO3 nanoparticles was found to be very sensitive and selective to low concentrations of acetone (0.2-1ppm) compared to a series of interfering gases at 400°C. The proposed explanation for the materials selectivity to acetone is the likely interaction between the surface dipole of ferroelectric ϵ-WO3 nanoparticles and the highly polar acetone gas molecules.
Open structured h-WO3 nanoparticles were produced by acid precipitation method. It was found that h-WO 3 is very sensitive to NOx compared to other gases at 150°C due to the open tunnel structure of h-WO3. Such selectivity is lost at 350°C. Instead, the material is very sensitive and selective to isoprene gas at 350°C. A p-n transition was found when the working temperature of the sensor increased from RT to 350°C which could be related to the excessive surface oxygen of the product.
Finally, a handheld exhaled breath analyzer prototype has been developed for non-invasive disease diagnosis. Real-time monitoring of the gas concentration is demonstrated, making this invention a revolutionary, non-invasive, diabetes diagnostic tool.
0794: Materials science