Mixed oxides as VOCs detectors in biomedical applications

Abstract

Mixed nanostructures based on zinc oxide (ZnO), copper oxide (CuO) and iron oxide (Fe₂O₃) were synthesized through thermal oxidation in air, and their gas sensing properties were investigated. The motivation for combining these oxides lies in their complementary semiconductor behaviour: ZnO and Fe₂O₃ are n-type materials, while CuO is a p-type material. Forming p–n junctions enhances charge transfer and increases surface reactivity, thereby improving sensitivity and selectivity. Structural characterization using scanning electron microscopy (SEM) revealed interconnected nanostructures with sponge-like morphologies. Gas sensing experiments were conducted using a Keithley 2400 source meter to evaluate the sensor response towards n-butanol, 2-propanol and acetone at concentration of 100 ppm within a temperature range of 22–275 °C. The highest response was observed for 2-propanol, followed by acetone and n-butanol, with optimal performance at 250–275 °C. Response and recovery times were found to be in the range of a few to tens of seconds, indicating good reversibility and repeatability. The sensing mechanism is governed by the interaction of adsorbed oxygen species with target gases, leading to electron release and changes in conductivity. The promising performance in detecting acetone highlights the biomedical potential of these mixed nanostructures, particularly for non-invasive breath analysis related to diabetes monitoring.