Metal oxide-based gas sensors for the detection of exhaled breath markers

Exhaled breath test is a typical disease monitoring method for replacing blood and urine samples that may create discomfort for patients. To monitor exhaled breath markers, gas biomedical sensors have undergone rapid progress for non-invasive and point-of-care diagnostic devices. Among gas sensors, metal oxide-based biomedical gas sensors have received remarkable attention owing to their unique properties, such as high sensitivity, simple fabrication, miniaturization, portability and real-time monitoring. Herein, we reviewed the recent advances in chemoresistive metal oxide-based gas sensors with ZnO, SnO₂ and In₂O₃ as sensing materials for monitoring a range of exhaled breath markers (i.e., NO, H₂, H₂S, acetone, isoprene and formaldehyde). We focused on the strategies that improve the sensitivity and selectivity of metal oxide-based gas sensors. The challenges to fabricate a functional gas sensor with high sensing performance along with suggestions are outlined.