Functionalizing a Tapered Microcavity as a Gas Cell for On-Chip Mid-Infrared Absorption Spectroscopy

A fiber-tip photoacoustic sensor for in situ trace gas detection

Most trace gas detection methods developed so far largely rely on active sampling procedures, which are known to introduce different kinds of artifacts. Here, we demonstrate sampling-free in situ trace gas detection in millimeter scale volumes with fiber coupled cantilever enhanced photoacoustic spectroscopy. Our 2.4 mm diameter fiber-tip sensor is free from the wavelength modulation induced background signal (a phenomenon that is often overlooked in photoacoustic spectroscopy) and reaches a normalized noise equivalent absorption coefficient of 1.3 × 10^-9 W cm^-1 Hz^-1/2 for acetylene detection. To validate its in situ gas detection capability, we inserted the sensor into a mini fermenter for headspace monitoring of CO₂ production during yeast fermentation. Our results show that the sensor can easily follow the different stages of the CO₂ production of the fermentation process in great detail.