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

The bacterium H.pylori is believed to cause peptic ulcer. H.pylori infectio n 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 rati o measurement realized in the ENEA Molecular Spectroscopy Laboratory is des cribed, The experimental apparatus consists of a IR tunable diode laser ope rating slightly above liquid nitrogen temperature and emitting multimode ra diation 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 i nto 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 a re detected by a sensitive HgCdTe detector and averaged on a digital oscill oscope. The spectra an transferred via a GPIB interface to a PC and elabora ted by a dedicated software. Eventually the obtained absorbance spectra are fitted to Gaussian profiles and relative (CO2)-C-13/(CO2)-C-12 concentrati ons have been obtained with high accuracy. Comparison between theoretical a nd experimental spectra has been performed by using the Hitran data base. C alibrating procedure and experimental results both on reference mixture and human breath are reported and discussed.