Development of a highly sensitive and versatile analytical technique by using laser-induced breakdown spectroscopy: Applications to aerosols and biological materials

The ns-duration pulsed laser-induced breakdown (10⁴ K and 10¹⁶ electron.cm^-3) spectroscopy (LIBS) is developed for characterizing every chemical or biological sample (gas, homogeneous or heterogeneous surface, and aerosol) in situ, rapidly (∼10^-6 s), in a sensitive and reproducible manner, for classification purposes, and even identification. The optically sampled volume is reproducible for the plasmas in gases (∼1 mm³) and on surfaces (diameter of impact∼10² μm²). The calibration of the technique is then possible for the multi-elementary measurement with limits of detection of about 1 ppm, and even 1 ppb, also comprising micron-sized particles. The spectral markers of biological materials (Ca, Mg, Na, K, P, and C) are identified by means of a statistical treatment based on a principal components analysis, which lets to classify the samples according to their nature. We study how the discriminating observables are detected for various bacterial kinds: compressed pellets of bulk freeze-dried bacteria, vegetative growths on Petri dishes with a measured minimal threshold of about 10³ Bacillus-typed bacteria, and suspended aerosols. The statistical exploitation of the spectral markers leads to distinguish bacteria both from their nutritive media, and interferon. In the case of direct on flight analysis of aerosolized bacteria, the detection is more complex and random due to the weak elementary available ratios, which necessitates their preliminary concentration. The LIBS technique, that has been calibrated for gases, surfaces and aerosols, is engineered under a transportable, versatile and sensitive tool adapted to numerous applications: biomedical diagnosis, on line monitoring of industrial processes, environmental quality control. (author)