Calibration-free Laser-induced Breakdown Spectroscopy (CF-LIBS): Plasma criteria for porcine tissue

Laser-induced Breakdown Spectroscopy (LIBS) has established itself as a powerful analytical method in industrial applications, effectively analysing a wide range of materials such as metals and polymers, and even identifying the material composition on Mars. Despite its proven benefits in industrial settings, LIBS has not been extensively studied in medical contexts, where its potential benefits remain largely unexplored. This research builds on the successful application of a LIBS system for metal analysis and extends its methodology to biological samples. The primary objective of this study is to evaluate the necessary conditions for calibration-free LIBS (CF-LIBS) analysis of porcine skin, muscle and fat, chosen for their similarities to human tissues. The three essential conditions for CF-LIBS are stoichiometric ablation, optically thin plasma and local thermodynamic equilibrium. To assess these conditions, the temperature was analysed using the Boltzmann plot, while the electron density was determined using the McWhirter criterion and the Saha-Boltzmann equation. These plasma criteria were carried out for the elements sodium, carbon, calcium, magnesium and iron. The results showed that it is possible to satisfy all three conditions for CF-LIBS for the elements studied, suggesting promising future applications of CF-LIBS in the analysis of biological tissues.