Different nanoparticle shapes for nanoparticle-enhanced laser-induced breakdown spectroscopy: nanosphere and nanorod effects

Nanoparticle-enhanced laser-induced breakdown spectroscopy (NELIBS) is the optical emission spectroscopy of laser-induced plasma obtained by laser ablation after the deposition of plasmonic NPs on the surface of a sample. The effect of the coupling of NP plasmons with laser pulse leads to a notable improvement of the analytical signal. In this work, different kinds of gold nanoparticles (AuNPs) are employed: spherical gold nanoparticles (AuNSs) and gold nanorods (AuNRs). Two AuNRs with the same diameter (10 ± 2 nm) but different lengths (50 ± 2 and 70 ± 2 nm) have been investigated in order to explore the AuNR size effect on the coupling between the incoming laser beam and AuNPs. LIBS and NELIBS experiments were performed on a Ti target with the aim of comparing the effects of AuNRs and AuNSs, deposited on the target surface, on the emission spectra. The SEM (scanning electron microscopy) micrographs of the AuNPs on the Ti target before and after the NELIBS experiments were used to analyze the AuNP distribution on the sample surface. The results show that the NP concentration per surface unit ( i.e. number of NPs per surface unit or mol of NPs per surface unit) is crucial for comparing NPs of different shapes or sizes used as enhancers. In this work, once the concentration is optimized for each NP shape, the results show that plasmon-enhanced ablation is moderately affected by the variation in NP shape, giving similar enhancement values for both types of employed AuNPs. Comparison between nanosphere and nanorod plasmonic coupling with the laser electromagnetic field in terms of signal enhancement obtained during NELIBS.