sample="quota" bates="2063593224" isource="pm" decade="1990" class="ui" date="19981000" Comments on "Lung Cancer Screening by Breath Analysis Groups Involved 1. Quadrivium LLC. POB 1421, Pebble Beach CA (venture capital group?) 2. U. Cal San Diego Medical Center 3. Argonne National Labs 4. Texas A&M New Star Lasers : lasers for medical uses, collaboration with Beckman Laser Institute of U. Cal., mainly Nd:YAG and Ho:YAG (no mention of CO2 lasers on their web site) 6. UCLA 7. HARC (?) As best I can tell from the limited scientific content of the video, the researchers propose to use a photoacoustic gas cell and a CO laser to measure specific selected VOCs in expired breath as a biomarker for the early detection of lung cancer. There is certainly evidence in the scientific literature that this technique should be able to detect a concentration of ppbV(ca. ng) of a specific analyte in a complex gas mixture (see attached literature search). Advantages include: high spectral resolution (0.017 cm-1) from the laser, high power density from the laser, large linear range of PA signal vs concentration (4 orders of magnitude), a zero background technique (like an emission expt) where all the signal is from the sample. In the experimental set-up, the laser is continuous wave (CW) and the light is chopped (amplitude modulated, AM), so that the resulting PA signal can be demodulated by a lock-in amplifier. I think AM rides on top of a constant DC offset which lowers the dynamic range of the LIA. Other types of modulators other than a chopper wheel are available, but I don't think they are applicable here (photoelastic modulator, opto-acoustic modulators, phase modulation from a Michelson interferometer). Most studies in the literature have used a CO2 laser (9.2 - 10.8 µm or 1020-926 cm-1). I am not sure why they propose to use a CO laser here, unless the researchers already know what lines of what analytes (acetone and 2-butanone) they need to monitor. I believe the uncertainty lies in the physiology of the malignant lung cancer itself: does it produce a large enough concentration of the chosen analyte to quantify (to choose a line free from interferences with a sufficient level of detection). The initial proof of principle study, growing cell cultures in a petri dish, should establish feasibility.