Observation of Peptide-Ion Generation by Laser-Induced Surface Heating from Tungsten Silicide Surfaces

We report observation of laser desorption/ionization (LDI) of peptides from flat surfaces of tungsten silicide (WSi2). In contrast to MALDI (matrix-assisted laser desorption/ionization) and SALDI (surface-assisted laser desorption/ionization) mass spectrometry, this study did not utilize any matrices and surface nanostructures. In this work, LDI on WSi2 surfaces is dem- onstrated to cover a mass range up to 1,600 Da (somatostatin; monoisotopic mass = 1637.9 Da). In addition, it exhibited a high sensitivity, which could detect peptides, which could detect peptides of low femtomole levels (20 fmol for angiotensin II). The observed LDI process was discussed to be largely thermal, more specifically, due to laser-induced surface heating that is most likely promoted by the low thermal diffusivity (κ) of WSi2 substrate.