Breath aerosol capture by electric field concentration

Project Summary This proposed project is aimed at developing a method for capturing and concentrating exhaled breath aerosols by electrostatically charging them and collecting them on sub-mm diameter areas for optimal trace aerosol detection sensitivity by infrared tunable laser spectroscopy (TLS). An immediate application for this technology is detection of trace amounts of the marijuana intoxicating aerosol ingredient tetrahydrocannabinol (THC), but other applications include detection of dangerous drugs and viruses. Prior work on spectroscopic sensing of THC at Vox Biomedical indicated that exhaled breath aerosol area concentration is needed because the sub-ng amounts of THC in exhaled breath aerosols are so small that the captured aerosols do not entirely cover the 1 cm2 sample areas typically used in infrared spectroscopy, thereby reducing system sensitivity. Modeling showed that aerosol concentration onto sub-mm diameter areas of diameter equal to the diffraction-limited focused TLS quantum cascade laser spot size enables optimal detection sensitivity, resulting in several orders of magnitude improved spectroscopic detection sensitivity because a much larger fraction of the focused probe laser light will be absorbed by the concentrated analyte. The required sub-mm diameter area THC aerosol analyte concentration will be achieved by electrostatically charging the exhaled breath THC aerosols and then accelerating the charged aerosols onto an electrically conducting silicon coupon covered with a non-conducting oxide layer into which a 0.1 mm diameter opening is photolithographically defined. This photolithographic wafer fabrication process will be carried out in a local semiconductor foundry. The design of the patterned silicon wafer will be such that the wafer can be sectioned into identical small coupons, each with a single 0.1 mm diameter oxide opening, that will then be used in the planned analyte deposition experiments. To demonstrate the efficacy of this proposed new aerosol concentration method during Phase I Vox Biomedical will first use a well-characterized Alphazurine-A dye obtained from a nebulizer and precision injected into a polycarbonate cylinder and charged by an electric field of several kV/cm as created by a cylindrically symmetric arrangement of three tungsten tip corona needles. Since the Alphazurine-A dye is well characterized by its known spectral absorption characteristics, it will be possible to determine the minimum detectible amounts of deposited dye aerosols. Following the Phase I Alphazurine-A dye concentration study, a more refined feasibility demonstration will be carried out using THC aerosols that will be generated by nebulizing methanol with quantitatively known THC concentrations obtained from commercial THC-in-methanol solutions. Phase II will then include human marijuana user exhaled breath measurements. Successful development of the proposed new electrostatic aerosol concentration method will provide both law enforcement and employee screening personnel with a non-invasive means for identifying marijuana and drug users in real time. If successful, this aerosol capture technique could also be applied to identifying exhaled breath virus content.