Laser-induced breakdown spectroscopy using a porous silicon substrate produced by metal-assisted etching: Microanalysis of strontium chloride aqueous solution as an example

Laser-induced breakdown spectroscopy (LIBS) of dry residues on a solid substrate is a promising method for microanalysis of liquid samples. In this work, a hydrophilized porous silicon (Si) substrate loaded with gold nanoparticles was applied to LIBS of dry residues for the signal enhancement. The porous Si substrate was prepared by a simple wet process, i.e. metal-assisted etching. A 5-µL strontium chloride aqueous solution was dried on the porous Si substrate and the dry residue was analyzed by a single-pulse scheme with a laser energy of 1.5 mJ/pulse. We successfully enhanced the strontium signal intensity over 150 times by using the porous Si substrate instead of a flat Si substrate. We also demonstrated that the signal intensity changed depending on the pore depth of the porous Si. The porous Si has great potential as a substrate for LIBS of dry residues.