Oxygen sensing without organic molecules: Mixed-phase TiO2 as cost-effective ultrasensitive optical sensors

Oxygen (O₂) detection is commonly carried out via either fluorescence-based optical sensors or chemoresistive sensors. Each approach has its own limitations. Optical sensors require the molecular design and synthesis of specific organic fluorescent species, which usually are costly and often display instabilities issues. Chemoresistive sensors, despite presenting advantages in using more cost-effective inorganic materials, are often limited by low sensitivities to O₂ at ppm concentrations and by their inability to operate at room temperature. In this work, we demonstrate the detection of O₂ at concentrations as low as a few tens of ppm at room temperature by using titanium dioxide (TiO2) mixed-phase nanoparticles as optical sensors. By simultaneously measuring the photoluminescence of nanoparticles in rutile and anatase phase, O₂ detection was achieved in the concentration range of 30–500 ppm, with a response curve well-calibrated by a Langmuir function. Good response promptness and repeatability are also demonstrated. This approach to O₂ optical sensing offers two intrinsic advantages over the most commonly used methodologies: (1) use of a more cost-effective, easy-to-prepare and stable sensitive material compared to those typically employed in optical sensing, and (2) improved room-temperature detection efficiency in the low O2 concentration range, outperforming most commonly-used chemoresistive sensors.