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Biological tissues contain various metals and metalloids ions with central role in the regulation of several pathophysiological functions. In parallel, the development and the evaluation of novel nanocompounds for biomedicine require the monitoring of their biodistribution in tissues of interest. Therefore, researchers need to use reliable and accessible techniques to detect and quantify major and trace elements in space-resolved manner. In this communication, we report how Laser-Induced Breakdown Spectroscopy (LIBS) can be used to image the distribution of chemical elements in brain tissues.

In this work, the main peculiarities of Laser Induced Plasma (LIP) in liquid have been investigated by comparing the evolution of the LIP in water and in air. To this end, fast shadowgraphy and temporally resolved emission spectroscopy were used. The experimental results reveal a scenario where plasma under water remains in a high-density state, characterized by the condensation of electronic levels as a consequence of the confinement effect of the surrounding water. In this case, the plasma emission spectrum consists of continuum radiation. In contrast, LIP in air expands, reaching an ideal plasma state in a few hundred nanoseconds. In this condition, excited electronic levels are enabled and the spectrum is characterized by discrete emission lines, according to the Boltzmann statistics. These differences allow LIP in liquid and gas to be used in a wide variety of applications, ranging from analytical chemistry to nanomaterial production.

Recently the use of nanoparticles (NPs) for enhancing Laser ablation based analytical techniques, is getting a growing interest in analytical atomic spectroscopy. This technique is based on the deposition of NPs on the sample surface before the laser irradiation. The effect of the coupling of NPs plasmon with the laser pulse allows a notable improvement of the analytical signal. In this study, different sizes of spherical gold nanoparticles (AuNPs), 10 nm, 40 nm, 60 nm and 100 nm, have been employed to clarify the role of the NPs size on the signal enhancement during Laser Induced Breakdown Spectroscopy (LIBS). Therefore, a systematic investigation of the Nanoparticle Enhanced LIBS (NELIBS) have been done by varying the key experimental parameters as NPs surface concentration, laser fluence and laser spot size. The experimental results show that improvement of the emission signal during NELIBS occurs at specific NPs surface concentration and that this critical concentration depends on the NP size. When the concentration has been optimized for each NP size, the plasmon-enhanced ablation is moderately affected by the NPs size.

In this paper the plasmon enhanced ablation for elemental analysis is investigated with several experiments in order to point out the crucial questions concerning the laser matter interaction under the effect of plasmonic coupling between the nanoparticle (NP) system and the laser ablation pulse. The correlation between the electromagnetic field enhancement and the signal enhancement during NP enhanced laser induced breakdown spectroscopy (NELIBS), as well as the laser matter interaction at the nanoscale, is discussed in the case of noble metal NPs deposited on metal samples. The results suggest that, while laser pulse energy is concentrated in the space between the NPs, the NP system is shielded by the field enhancement distribution after the laser pulse interacts with the plasmons of the NP system. Finally the comparison of the laser energy transfer to the sample between NELIBS and conventional LIBS is discussed.