“…Although breath contains many kinds of gas species, including water (H 2 O), carbon monoxide (CO), carbon dioxide (CO 2 ), nitrogen (N 2 ), ammonia (NH 3 ), nitrogen monoxide (NO), hydrogen sulfide (H 2 S), and more than 1,000 kinds of volatile organic compounds (VOC) [13], the simple molecular structures of these low molecular compounds make it difficult to achieve specific molecular recognition compared with biomarkers having complex molecular structures, such as proteins. Therefore, a recent strategy is based on chemometrics, which are comprised of pattern-recognition protocols of multiple signals obtained from sensor arrays with different selectivities [14].…”