Laser Ablation of Organic Materials for discrimination of bacteria in an organic background

We demonstrate in this paper that laser ablation allows efficient analysis of organic and biological materials. Such analysis is based on laser-induced breakdown spectroscopy (LIBS) which consists in the detection of the optical emission from the plasma induced by a high intensity laser pulse focused on the sample surface. The optimization of the ablation regime in terms of laser parameters (pulse duration, wavelength, fluence) is important to generate a plasma suitable for the analysis. We first present the results of a study of laser ablation of organic samples with different laser parameters using time-resolved shadowgraph. We correlate the early stage expansion of the plasma to its optical emission properties, which allows us to choose suitable laser parameters for an efficient analysis of organic or biological samples by LIBS. As an illustration of the analytical ability of LIBS for biological materials, we show that the emission from CN molecules can be used to distinguish between biological and inorganic samples. Native CN molecular fragment directly ablated from a biological sample are identified using time-resolved LIBS. Those due to recombination with nitrogen contained in atmospheric air can be distinguished with their specific time evolution behavior.