The use of laser-induced breakdown spectroscopy (LIBS) for analysis of micro- and nanoparticles is explored, including a brief review of the recent research, both fundamentals and applications, along with new experimental work regarding aerosol particle sampling statistics, analysis of laser ablation particles via aerosol LIBS for matrix effect minimization for bulk solids analysis, and a novel aerosol particle concentration scheme that is suited for near real-time analysis of aerosol nanoparticles. The statistical analysis reveals that the LIBS particle sampling physics are well modeled using Poisson sampling statistics, as based on analysis of calcium-rich ambient air particles. The laser-ablation LIBS (LA-LIBS) methodology was explored for a range of disparate metallic and non-metallic bulk samples, revealing a linear calibration curve for all six samples over the range of relative Mn/Fe mass concentrations. Finally, the microneedle concentration technique for aerosol nanoparticle analysis was successfully demonstrated with linear mass calibration curves for copper-rich nanoparticles. Overall, a fundamental understanding of the plasma–particle physics has enabled the formulation of robust LIBS-based nanoparticle schemes.
Plasmaparticle interactions are explored through the introduction of single microdroplets into laser-induced plasmas. Both spectroscopic analysis and direct imaging of analyte atomic emission are used to provide insight into the various fundamental processes, namely desolvation, atomization, and atomic diffusion. By doping the 50 µm droplets with Lu, Mg or Ca, the analyte excitation temperature and the ion-to-neutral emission ratio are explored as a function of plasma residence time following breakdown. The data suggest a change in the local plasma conditions about the analyte atoms around 1520 µs following breakdown, which may be interpreted as an overall transition from localized (i.e. perturbed) plasma conditions to the global (i.e. bulk) plasma conditions. A direct assessment of the hydrogen atomic diffusion coefficient following analyte desolvation reveals a value of 1.7 m² s-1 in the first 250500 ns. This value is in good overall agreement with a theoretical analysis and with an analytical treatment of a surface source of hydrogen atoms. In contrast, calcium emission is only observed beyond about 1 µs, with a diffusion coefficient at least an order of magnitude below the hydrogen value. The temporal H and Ca emission data suggest that water vaporizes first, leaving an ever increasing Ca analyte concentration until finally, with nearly all water desorbed, the Ca fraction is vaporized. Overall, the data support the conclusion that finite time-scales of heat and mass transfer play an important role in localized plasma perturbations in the vicinity of the analyte, which has important implications for the LIBS analyte signal.