Real time detection of exhaled human breath using quantum cascade laser based sensor technology

The development and performance of a cw, TE-cooled DFB quantum cascade laser based sensor for quantitative measurements of ammonia (NH3) and nitric oxide (NO) concentrations present in exhaled breath will be reported. Human breath contains similar to 500 different chemical species, usually at ultra low concentration levels, which can serve as biomarkers for the identification and monitoring of human diseases or wellness states. By monitoring NH3 concentration levels in exhaled breath a fast, non-invasive diagnostic method for treatment of patients with liver and kidney disorders, is feasible. The NH3 concentration measurements were performed with a 2f wavelength modulation quartz enhanced photoacoustic spectroscopy (QEPAS) technique, which is suitable for real time breath measurements, due to the fast gas exchange inside a compact QEPAS gas cell. A Hamamatsu air-cooled high heat load (HHL) packaged CW DFB-QCL is operated at 17.5 degrees C, targeting the optimum interference free NH3 absorption line at 967.35 cm(-1) (lambda similar to 10.34 mu m), with similar to 20 mW of optical power. The sensor architecture includes a reference cell, filled with a 2000 ppmv NH3 :N-2 mixture at 130 Torr, which is used for absorption line-locking. A minimum detection limit (1 sigma) for the line locked NH3 sensor is similar to 6 ppbv (with a 1 sigma; 1 sec time resolution of the control electronics). This NH3 sensor was installed in late 2010 and is being clinically tested at St. Luke's Hospital in Bethlehem, PA.