Manufactured nanoparticles detection using LIBS
Résumé
Today, nanotechnology is a growing field of research and nanoparticle-based material production is expected to soar in years to come. Though research is still currently under way to secure nanoparticle production processes, the risk of accidental release is not to be neglected. Consequently, there is an urgent need for the manufacturer to have at their command a tool enabling leak detection in-situ and in real time so as to protect workers from potential exposure. Currently, most of the available tools do not allow differentiating manufactured nanoparticles from those of background air, thereby rendering targeted nanoparticle detection arduous. Such problem may be addressed by chemically identifying nanoparticles. To achieve this goal, the LIBS (Laser-Induced breakdown Spectroscopy) technique was deemed as a potential candidate. LIBS measurements consist in focusing a powerful laser pulse on a material which elemental composition is to be determined. At the focus spot, the matter whatever its state be (solid, liquid, gas, aerosol) is strongly heated resulting thereby in the generation of a hot and luminous ionised gas called plasma. Elemental composition of the irradiated target is then determined through plasma analysis by optical emission spectroscopy. This method is not intrusive and does not require sampling. It allows in-situ and real time analysis. These qualifies are advantages over other techniques as the LIBS analyser is intended to be operated on the production sites : no sample preparation required, in-situ and real time detection and survey for a wide range of on-site application. Research studies up to technical optimizations were realized on laser / plasma / particle interaction sin order to further achieve LIBS measurements with optimum efficiency. Polydisperse and monodisperse flows of salt and metallic particles with sizes ranging from 40 nm up to 1 um produced by two different particle generators were introduced inside a cell for where they were vaporized by the laser induced plasma for LIBS analysis purposes. Time-resolved emission spectroscopy measurements were carried out and the influence on the LIBS signal of parameters such as chemical nature of particles, their concentration, laser wavelength, laser energy, kind of background gas was investigated. Then, calibration curves and limit of detection have been investigated for a wide range of metallic particles (Ti, Al, Cu...). These results allowed to make a first assessment of LIBS potentialities for manufactured nanoparticle detection in workplace. Based on these laboratory results, INERIS is currently associated with an industrial partner to build a tool dedicated for in situ measurement purpose.