Volatile organic compounds (VOCs) in exhaled breath have been identified as potential biomarkers for various medical conditions. Electronic nose (e-Nose) devices integrated with metal oxide (MOx) sensors are used for VOC detection because they are highly stable, sensitive to a broad range of analytes and offer rapid detection and portability for point of care applications. Since MOx sensors respond to an array of VOCs, it is important to understand sensor behavior when exposed to synthetic VOCs profiles before translating these devices to biological samples in real world applications. The current study focused on characterizing the response of a tin oxide sensor when exposed to individual and mixtures of VOCs. Five candidate VOC biomarkers (acetone, isopropanol, limonene, nonanal, and isoprene) previously reported for diseases (cirrhosis, lung cancer, ovarian cancer and diabetes) and their associated concentrations in breath were identified and used for simulated breath analysis. The simulated breath profiles were used to evaluate the nanosensor capability to distinguish VOC biosignatures. The impact of humidity on sensor performance was assessed by conducting the experiment at 45% and 85% relative humidity (RH), which are the lower and upper humidity levels in breath. Once synthetic VOC profiles were studied, the researchers explored sensor sensitivity and selectivity toward individual VOCs to gain a better understanding of sensor response. Experimental findings showed that synthetic VOCs mixtures were distinguishable with 100% sensitivity and specificity regardless of humidity level, thus underlaying the sensors low sensitivity toward humidity. Calibration curves were constructed for the five VOCs of interest to determine sensitivity, selectivity, limit of detection and limit of quantification. These results were used to help understand the MOx sensing mechanism, which relies on oxidation–reduction reactions between the sensing layer and VOCs of interest. These findings help realize the potential of tin oxide nanosensors as a noninvasive, easy to use, and reliable diagnostic device for the detection of VOC biomarkers in exhaled breath at a point of care setting.

Quantifying the sensitivity and selectivity of portable tin oxide nanosensors to detect VOC biomarkers in simulated breath samples

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