A TDLAS system for the diagnosis of Helicobacter pylori infection in humans

The bacterium H.pylori is believed to cause peptic ulcer. H.pylori infection in the human stomach can be detected through a CO2 isotopic ratio measure in expired breath. In the present work the Tunable Diode Laser Absorption Spectroscopy optical system (TDLAS) dedicated to (CO2)-C-13/(CO2)-C-12 ratio measurement realized in the ENEA Molecular Spectroscopy Laboratory is described, The experimental apparatus consists of a IR tunable diode laser operating slightly above liquid nitrogen temperature and emitting multimode radiation around 2305 cm(-1) where strong absorption lines of CO2 are present. Mode selection has been performed with a 50 cm focal length monochromator. A sample of human breath is collected in a balloon and then transferred into a White type multipass cell (2 m of optical path) whose exit window is coupled to the entrance slit of a monochromator. The transmission spectra are detected by a sensitive HgCdTe detector and averaged on a digital oscilloscope. The spectra an transferred via a GPIB interface to a PC and elaborated by a dedicated software. Eventually the obtained absorbance spectra are fitted to Gaussian profiles and relative (CO2)-C-13/(CO2)-C-12 concentrations have been obtained with high accuracy. Comparison between theoretical and experimental spectra has been performed by using the Hitran data base. Calibrating procedure and experimental results both on reference mixture and human breath are reported and discussed.