12. MAPLE and MALDI: Theory and Experiments

Laser induced breakdown spectroscopy (LIBS) and pulsed laser deposition (PLD) are important techniques for the analysis of materials and the fabrication of thin films (metals, alloys and inorganic compounds). These techniques are not applicable to polymers, organic and biomaterials, mostly destroyed by the energetic laser pulses. To overcome this drawback, matrix assisted laser techniques were introduced: matrix assisted laser desorption ionization (MALDI) and matrix assisted pulsed laser evaporation (MAPLE), for mass spectroscopy and thin film deposition, respectively. They offer an efficient mechanism to transfer easy-to-be-decomposed materials from the condensed phase into the vapor phase. The material of interest (polymers, biological cells, proteins…) is diluted in a volatile solvent, with a typical concentration of a few wt%, to form the target to be irradiated with a pulsed laser beam. The laser energy is principally absorbed by the solvent and converted to thermal energy, allowing the solvent to vaporize. The molecules of the material of interest receive enough kinetic energy through collective collisions with the evaporating solvent to be transferred in the gas phase and finally analyzed or deposited on a suitable substrate. Here, important results of MALDI and MAPLE are reported and their working mechanisms are discussed.