Size-dependent plasma–nanoparticle interactions in Laser Induced Breakdown Spectroscopy

The detection of nanoparticles (NPs) by Laser-Induced Breakdown Spectroscopy (LIBS) is gaining increasing interest in the analytical chemistry community, both for the elemental analysis of the NPs themselves and in view of their use as tags in biomedical applications. In the present work, the origin and characteristics of the atomic emission signal produced by NP vaporization during LIBS were investigated both experimentally and theoretically, focusing on the effect of NP size (ranging from 5 to 100 nm) on the sensitivity of calibration curves. To this end, we determined the dependence of the calibration curve slope on the NP size, so to assess the effect of NP dimensions on the production of emitters and consequently on the emission analytical signal. LIBS was tested on AuNPs and AgNPs deposited on different substrates: nitrocellulose paper, silicon and copper. It was observed that, although smaller NPs vaporize more efficiently according to the Gibbs-Thomson theory, the larger surface area of bigger NPs results in a higher evaporation yield in terms of the total number of atoms. Consequently, larger NPs generate more emitters and lead to lower limits of detection.