“…However, most of the developed instrumental techniques are typically complex, expensive and not suitable for diagnostic application. In addition, a number of the methods contribute to pre-analytical errors due to issues such as sample transportation and handling.While a number of sensor-based approaches have been developed including quartz crystal microbalance (Becker and Cooper, 2011;Ishida et al, 2008;Ogimoto et al, 2015), chemical and optical sensors, many of these have had challenges in terms of detection limits, or operation in real humidified breath samples, which has made them unsuitable for physiological application. However, some have now demonstrated effective application in human clinical studies (Hibbard et al, 2013).…”