https://hdl.handle.net/11375/32647

Mahtab Taheri (2026) Low-cost flexible metal oxide-based sensors for temperature and pH monitoring, MacSphere - Theses & Dissertations, https://hdl.handle.net/11375/32647

The demand for flexible, manufacturable, and affordable sensors is growing, but many state-ofthe-art devices still rely on rigid substrates and costly vacuum processing. This thesis investigates two separate sensing modalitiespH and temperatureimplemented with metal oxidecarbon composites processed at low temperature on flexible substrates, emphasizing solution/printing routes, mechanical compliance, and long-term stability. For pH sensing, ruthenium oxide (RuO?) was integrated with graphene oxide (GO) to form a composite film on screen-printed carbon electrodes. The electrode stack and deposition sequence were optimized to improve adhesion, accessible surface area, and interfacial charge transfer. The resulting sensors exhibited near-Nernstian response with high linearity, rapid response across repeated pH cycles, and low drift over multi-hour testing, while maintaining robust performance in the presence of common interfering ions across concentrations. Temperature-dependence experiments quantified the slope variation and informed practical compensation strategies. Structural and morphological characterization (SEM, EDS, XRD, Raman Spectroscopy) corroborated the composite architecture and linked film features to electrochemical behavior. For temperature sensing, a negative-temperature-coefficient thermistor was realized using a NiO/graphene/polystyrene (NiO/Gr/PS) composite patterned on flexible polymer substrates via low-temperature, solution-based processing. By varying NiO and polymer content, the resistance temperature relation could be tuned from near-linear to exponential, enabling extraction of the thermistor material constant (B-value) and optimization for sensitivity. The devices operated over ?10 to 50 C, showed small-signal temperature resolution, low hysteresis on heatingcooling cycles, drift stability over weeks, and environmental robustnessincluding humidity tolerance attributable to the polymer phase, mechanical resilience under bending (fixed-radius cyclic tests), and chemical stability after prolonged water exposure. Demonstrations included real-time tracking on curved, warm surfaces to illustrate practical responsiveness. Materials analysis (XRD, SEM/EDS cross-sections) confirmed phase content, dispersion, and film integrity. Collectively, these two independent studies establish low-temperature, solution/printing fabrication of metal oxidecarbon composites as a viable route to flexible, low-cost pH and temperature sensors with strong sensitivity, repeatability, and durability. The materials and process insights provide a foundation for future multi-sensor platforms and scalable manufacturing of conformable monitoring technologies.

Monitoring temperature and acidity (pH) is crucial in many areas of daily life, from ensuring the freshness of products to protecting human health and the environment. However, most available sensors are expensive, rigid, and not designed for portable or disposable use. This creates a need for affordable, lightweight, and flexible sensors that can provide accurate measurements outside of traditional laboratory settings. This thesis presents two separate studies that address this challenge. In the first, flexible devices were developed to measure pH. These sensors showed quick and reliable responses to changes in acidity and were stable over repeated use and extended periods of time. In the second study, flexible temperature sensors were created that responded rapidly to changes in temperature, operated consistently over a wide range, and remained functional even when bent, exposed to moisture, or tested over long durations. The research demonstrates that sensors can be produced at low cost using straightforward fabrication methods, while still achieving the sensitivity, stability, and robustness needed for practical applications. Together, the studies highlight how flexible and affordable monitoring devices can be realized, providing a foundation for future technologies that are simple to use, reliable, and accessible to a broad range of users.

https://hdl.handle.net/11375/32647