Lotus-Leaf-Inspired Surface-Fluorinated Indium Oxide Nanomastoid for Humidity-Resistant Hydrogen Sulfide Detection in Exhaled Breath

Abstract Non-invasive breath testing has emerged as a promising technique for real-time disease monitoring and early intervention. In the oral cavity, hydrogen sulfide (H2S) is predominantly generated through the metabolic degradation of sulfur-containing amino acids by Gram-negative anaerobic and Gram-positive bacterial communities. Precise quantification of exhaled H2S concentrations enables effective diagnosis of oral diseases, providing critical insights for clinical treatment strategies. However, the complex gas composition and high humidity of exhaled breath pose significant challenges for trace H2S detection due to interference effects. Herein, we report the fabrication of a surface-fluorinated indium oxide (In2O3) nanomastoid sensitive material via SF6 reactive ion etching. This engineered material mimics the multiscale hierarchical architecture of lotus leaves, integrating micron-sized mastoid protrusions with nanoscale fluorinated domains. The synergistic effect of the unique nanostructure and surface fluorination endows the sensor with excellent humidity-resistant H2S response kinetics. The sensor exhibits a stable response over the humidity range from 0 to 75% relative humidity (RH), with response values to 5 ppm H2S of 4.01 at 0% RH and 3.98 at 75% RH. Furthermore, under 100% RH in the presence of 4% CO2 as a typical interferent, the sensor maintains reliable detection of H2S at the ppb level, with a sensitivity of 1.35 and a theoretical detection limit of 37 ppb under such conditions. Experimental validation includes trace-level H2S detection in the exhaled breath of different volunteers and self-monitoring of post-toothbrushing H2S dynamics. The developed sensor system achieves tens of ppb level resolution, capable of detecting subtle H2S concentration changes while triggering an alarm upon detection of abnormal concentrations. To elucidate the underlying sensing mechanism and moisture-resistant origin, we conducted density functional theory calculations combined with in situ Fourier transform infrared spectroscopy experiments, which aim to analyze the surface chemical states and gas–material interaction behaviors of the fluorinated In2O3 nanomastoid structures under air or H2S gas, as well as under dry or humid environments. This work provides a robust material and sensor platform for trace H2S detection in high-humidity complex gas matrices, highlighting its significant clinical potential for non-invasive oral disease screening and personalized healthcare management.