Humidity-independent acetone gas sensors with ppbv-level sensitivity and high selectivity, using an In2O3 microporous nanoneedle array

Abstract

The detection of ppbv-level acetone is critical for the non-invasive diagnosis of diabetes and assessment of metabolic conditions. Highly sensitive humidity-independent gas sensors are required to achieve this goal. However, conventional semiconductor metal oxide (SMO) sensors often exhibit reduced performance in humid air. To overcome these limitations, we synthesized an In₂O₃ microporous nanoneedle array via chemical bath deposition and thermal treatment. These nanoneedles, composed of 3.4 ± 0.8 nm nanocrystallites, were meticulously arranged into well-ordered nanorods. The array featured pores with a diameter of 1.78 nm and exhibited both cubic and hexagonal phases of In₂O₃. The nanoneedles were formed through heterogeneous nucleation on the alumina substrate, followed by vertical and lateral growth, which produced self-standing porous structures with increasing size over the deposition time. The In₂O₃ microporous nanoneedle array sensors demonstrated exceptional sensitivity to acetone among 7 VOC gases, achieving a noteworthy response (R_a·R_g⁻¹ = 8.17 at 100 ppbv). The experimental and theoretical limits of detection (LOD) for acetone in dry air were 5 ppbv and 152 pptv, respectively. Notably, the sensor maintained an experimental LOD of 10 ppbv for acetone at 90% relative humidity (R_a·R_g⁻¹ = 2.98 at 10 ppbv). Moreover, the sensors exhibited excellent reproducibility, fast response/recovery times, and good long-term stability. Appropriate control of the nanostructure morphology contributes to achieving humidity-independent acetone sensing without the need for hybrid materials or noble metal catalysts. This approach provides a practical and reliable strategy for acetone sensing in humid atmospheres, supporting early diabetes screening and monitoring of metabolic conditions.