MOF-Derived SnO ₂ /MXene Heterostructure for ppb-Level Rapid and Selective Hydrogen Sensing toward Lactose Intolerance Diagnosis

Hydrogen (H 2 ) in exhaled breath serves as a key indicator for diagnosing lactose intolerance and small intestinal bacterial overgrowth, as its concentration increases significantly in affected individuals after carbohydrate ingestion. Thus, noninvasive detection of trace H 2 offers an effective method for early diagnosis and monitoring of gastrointestinal disorders. In this work, a SnO 2 /Ti 3 C 2 T x MXene heterojunction sensor was constructed by using metal–organic framework (MOF)-derived SnO 2 nanoparticles, achieving ultrafast hydrogen sensing at low temperatures. The sensor showed a 16.14% response to 300 ppb of H 2 within 1 s at 70 °C, with a detection limit as low as 5.19 ppb. It exhibited excellent stability, humidity tolerance, and high selectivity. DFT calculations and in situ Raman spectroscopy reveal that gas response arises from direct reconstruction of the unique interfacial electronic structure. The sensor distinguishes between simulated breath of lactose-intolerant and healthy individuals, showing strong potential for clinical diagnostics and gastrointestinal monitoring.