Quartz-enhanced photo-acoustic spectroscopy for breath analyses

Abstract

An innovative and novel quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor for highly sensitive and selective breath gas analysis is introduced. The QEPAS sensor consists of two acoustically coupled microresonators (mR) with an off-axis 20 kHz quartz tuning fork (QTF). The complete acoustically coupled mR system is optimized based on finite element simulations and experimentally verified. Due to the very low fabrication costs the QEPAS sensor presents a clear breakthrough in the field of photoacoustic spectroscopy by introducing novel disposable gas chambers in order to avoid cleaning after each test. The QEPAS sensor is pumped resonantly by a nanosecond pulsed single-mode mid-infrared optical parametric oscillator (MIR OPO). Spectroscopic measurements of methane and methanol in the 3.1 µm to 3.7 µm wavelength region is conducted. Demonstrating a resolution bandwidth of 1 cm −1 . An Allan deviation analysis shows that the detection limit at optimum integration time for the QEPAS sensor is 32 ppbv@190s for methane and that the background noise is solely due to the thermal noise of the QTF. Spectra of both individual molecules as well as mixtures of molecules were measured and analyzed. The molecules are representative of exhaled breath gasses that are bio-markers for medical diagnostics.

Infrared Non‐Invasive Exhaled Biomarker Sensing: A Review

“…[153] Minimum detection limit of 32 ppb with response time of 190 s was realized with QEPAS sensor with optical parametric oscillator (OPO) as a light source for detecting exhaled human breath at 3.1-3.7 μm range. [154] Using bandpass filter with 12 nm FWHM with centre wavelength of 1.65 μm can reduce the moisture-based interference. [155] In recent years, researchers are using QCL and interband cascade laser (ICL) as a laser source than other sources for detection of methane in the range of mid-IR regions.…”

“…[ 153 ] Minimum detection limit of 32 ppb with response time of 190 s was realized with QEPAS sensor with optical parametric oscillator (OPO) as a light source for detecting exhaled human breath at 3.1–3.7 µm range. [ 154 ]…”

Optimal-order preconditioners for the Morse–Ingard equations

“…Laser absorption spectroscopy is used for detecting trace amounts of gases, with applications to diverse fields such as air quality monitoring, disease diagnosis, and manufacturing [2,3,4]. One particular approach is photoacoustic spectroscopy, in which a laser is fired between the tines of a small quartz tuning fork.…”