Hierarchically ordered 2D/1D Bi₂O₂S/Bi₂S₃ heterostructure enabled by topotactic transformation for ppb-level NO sensing under humid conditions

Exhaled nitric oxide (NO) is a clinically relevant noninvasive breath biomarker associated with asthma diagnosis and management, yet its reliable detection remains hindered by the high humidity of human breath. Here, we develop a humidity-enhanced sensing strategy through template-guided topotactic transformation. The resulting hierarchically ordered 2D/1D Bi₂O₂S/Bi₂S₃ (BOS/BS) heterostructure features an open nanoarchitecture, facilitating rapid gas transport and exposing active sites. The optimized BOS/BS sensor delivers a response of 37 to 1 ppm NO at room temperature under 90% RH, with response/recovery times of 9/33 s and a detection limit of 25 ppb. The response is nearly 12 times that of the single-phase BS sensor and 4 times that of the less ordered BOS/BS sensor Rather than excluding moisture, the BOS/BS heterostructure integrates interfacial charge redistribution with humidity-induced surface hydroxylation to promote NO adsorption and conversion. This work establishes a topotactic route to hierarchically ordered heterostructures for room-temperature NO sensing under high humidity and offers a materials-design strategy for breath-relevant NO sensing under moisture-rich conditions.