Hydrothermal synthesis of flower-like In₂O₃ as a chemiresistive isoprene sensor for breath analysis

Isoprene is a typical biomarker for advanced fibrosis and can be used to screen and grade chronic liver disease (CLD). To detect trace isoprene, the high specific surface area (77.38 m²/g), porous flower-like In₂O₃ hierarchical microsphere material was prepared by simple hydrothermal method. In addition, the sensor based on synthetic flower-like In₂O₃ microspheres was prepared and gas sensing properties were investigated. The results showed that flower-like In₂O₃ nanomaterials had the highest response to isoprene at 190 °C. The response time was 53 s and repeatability was good. The relatively low operating temperature (190 °C) could extend the working life and also facilitate the portable application of the sensor. Meanwhile, the sensor exhibited selectivity over other typical biomarkers (ammonia, ethanol, hydrogen, and carbon monoxide). The unmodified pure flower-like In₂O₃ material could detect 5 ppb of isoprene at 190 °C and the logarithm of the response had good linear relationship with the logarithm of the concentration. Thus, this flower-like In₂O₃ material was promising to be developed into the portable breath isoprene detector that could be integrated into a micro system for noninvasive rapid screening and grading of CLD.