Investigation on Cr₂O₃@In₂O₃ Nanolamina Sensor with Heterojunction for Detecting ppb-level Isoprene in Breath

Ultratrace amounts of isoprene in exhaled breath are a well-distinguished biomarker for lung cancer, and detecting isoprene by a sensor can be a fast and non-invasive screening method. However, a significant challenge lies in sensing sensitivity, selectivity, and humidity resistance to detect ppb-level of isoprene in breath, which relies on expensive noble-metal-based materials. Herein, this work develops cost-effective In 2 O 3 -based sensors with nanoflower morphology assembled by 2D nanolaminae that facilitates the diffusion of low-concentration isoprene to attain high sensitivity. Transition metal oxides (e.g., Cr and Cu) were introduced to modulate the electronic structure by constructing a heterojunction for enhanced humidity resistance. As-prepared Cr 2 O 3 @In 2 O 3 nanolamina presents a high surface area of 71.7 m 2 ‧g -1 and active surface oxygen species of 57.9%, while the Cu doping disrupts the nanolamina structure of In 2 O 3 support due to the aliovalent interactions. Consequently, Cr 2 O 3 @In 2 O 3 nanolamina exhibits a detection limit of 10 ppb isoprene with good selectivity, and it is highly resistant to water vapor in exhaled breath, and demonstrates good stability during long-term operation. These findings demonstrate Cr 2 O 3 @In 2 O 3 nanolamina as a viable candidate for the detection of isoprene in breath, and verify the effectiveness of non-noble metal doping for applications of highly sensitive and stable gas sensors.