Drug precursor vapor phase sensing by cantilever enhanced photoacoustic spectroscopy and quantum cascade laser

Chemical control is a crucial element for controlling the manufacturing and distribution of illegal narcotics and synthetic substances. This work is focusing on the vapor phase point detection methodology due to its applicability in customs, airport and harbor check point scenarios where inspection of trucks, cars, containers, as well as people and baggage is required. There are several techniques available that are able to screen and identify specific molecules even at very low concentration at laboratory or in controlled environment. However, a portable system which would be simple to use, sensitive, compact, and capable of providing screening over a large number of compounds and discriminate them with low probability of false alarms with short response time scale is still demanded. Our solution is to combine cantilever enhanced photoacoustic spectroscopy with external cavity quantum cascade laser (EC-QCL), which is capable of measuring infrared gas phase spectra of the analyte substances. High sensitivity in a wide dynamic range is achieved with a silicon MEMS cantilever sensor coupled with an optical readout system and high power laser source, which is operating at the fundamental vibrational absorption wavelengths. High selectivity is achieved by measuring the infrared spectra of the sample gas utilizing widely tunable EC-QCL technology and novel signal processing methods. Measurements with the breadboard demonstrator of the described system and detection limit estimation were performed to a selected drug precursor target molecules. The measurement results indicate low ppb-level gas phase sensitivity to selected drug precursor substances also in the presence of typical interfering molecules.