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

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.

Parallel-plate compression test for soft materials: confocal microscopy-assisted ferrule-top nanoindentation.

The parallel-plate compression test is one of the simplest ways to measure the mechanical properties of a material. In this test, the Young's modulus ( E ) and the Poisson's ratio ( ν ) of the material are determined directly without applying any additional modelling and parameter fitting in the post-processing. This is, however, limited when dealing soft biological materials due to their inherent properties such as being inhomogeneous, microscopic, and overly compliant. By combining an interferometry-assisted parallel-plate compression system and a confocal microscope, we were able to overcome these limitations and measure the E (315 ± 52 Pa) and ν (0.210 ± 0.043) of fixated and permeabilized bovine oocytes.