Real-Time Measurement of CH4 in Human Breath Using a Compact CH4/CO2 Sensor

Abstract

The presence of an elevated amount of methane (CH4) in exhaled breath can be used as a non-invasive tool to monitor certain health conditions. A compact, inexpensive and transportable CH4 sensor is thus very interesting for this purpose. In addition, if the sensor is also able to simultaneously measure carbon dioxide (CO2), one can extract the end-tidal concentration of exhaled CH4. Here, we report on such a sensor based on a commercial detection module using tunable diode laser absorption spectroscopy. It was found that the measured CH4/CO2 values exhibit a strong interference with water vapor. Therefore, correction functions were experimentally identified and validated for both CO2 and CH4. A custom-built breath sampler was developed and tested with the sensor for real-time measurements of CH4 and CO2 in exhaled breath. As a result, the breath sensor demonstrated the capability of accurately measuring the exhaled CH4 and CO2 profiles in real-time. We obtained minimum detection limits of ~80 ppbv for CH4 and ~700 ppmv for CO2 in 1.5 s measurement time.

Chemiresistors Based on Hybrid Nanostructures Obtained from Graphene and Conducting Polymers with Potential Use in Breath Methane Detection Associated with Irritable Bowel Syndrome

“…A structure of a resistor was generated, with an active surface of about 1 cm 2 , limited by two metalized areas forming the conductive connections. Its functionality as a gas sensor was tested using an experimental system, similar to the one described in [62]. The sensor was introduced in a closed enclosure, which only allowed the exchange of gases by two valves and access to the electrical connections.…”

“…The sensor sensitivity can be clearly put in relation to the active surface of the sensor exposed to the targeted gas, and in our case, the surface architecture of the graphene structure with F8T2 presents a larger active surface due mainly to higher and more dense peaks, as noticed in Figures 9 and 11. But, if the application for testing the breath methane detection associated with irritable bowel syndrome is targeted, lower CH 4 concentrations in air must be detected, with a value of, e.g., 100 ppm, which may indicate the syndrome occurrence [62,63]. In this case, a new experimental calibration curve was analyzed, Figure 14.…”

“…Here, one can notice that both curves have a high degree of linearity for this CH 4 concentration domain but the slope for graphene structure with F8T2 is 6 times higher compared with the graphene structure with P3HT, which makes this structure more sensitive, feasible, and reliable for medical application. The inferior limit of CH 4 concentration detection, here 50 ppm, is considered enough when taking into account the correlation of CH 4 production with the severity of irritable bowel syndrome because lower concentrations do not particularly indicate a real occurrence of irritable bowel syndrome, [62,63]. In some studies, e.g., as described in [64,65], lower concentrations of CH 4 (20-40 ppm) were also analyzed but only for the purpose of detecting specific intestinal bacterial overgrowth, which may eventually influence the occurrence of irritable bowel syndrome; however, this approach was not the purpose of this paper as it targets the already established irritable bowel syndrome.…”

“…ularly indicate a real occurrence of irritable bowel syndrome, [62,63]. In some studies, e.g., as described in [64,65], lower concentrations of CH4 (20-40 ppm) were also analyzed but only for the purpose of detecting specific intestinal bacterial overgrowth, which may eventually influence the occurrence of irritable bowel syndrome; however, this approach was not the purpose of this paper as it targets the already established irritable bowel syndrome.…”