Laser-based trace gas detection for applications within biology and medicine

Abstract

Laser photoacoustic spectroscopy offers an elegant and relatively simple way to perform highly sensitive trace gas detection, owing in particular to the background free nature of this technique. As the photoacoustic signal is directly proportional to the laser power and to the absorption strength, it is advantageous to use powerful laser sources in the mid-infrared wavelength region (3−5 μm) where most molecules possess strong absorptions due to their fundamental vibrations. These instruments typically reach detection limits around 1 part per billion for small molecules and possess a time resolution of only a few minutes. This has made lasers applicable for a wide variety of applications in biological and medical research.
The gas concentrations of volatile metabolites may give valuable information on a large variety of processes inside biological tissue. Ripening and fermenting stages of fruits can be assessed, which is important for its storage and transport conditions. Oxidative stress and pathogenic attack in plants and fruit was also studied during chilling stress (cucumber leaves), submergence (rice seedlings) and bacterial infection (tobacco leaves and tomatoes).
That the potential of the laser-based gas detection systems could be extended to medical sciences was shown with the detection of exhaled trace gases from the human breath as during UV radiation induced damage to the human skin.