Effects of thin-film structural parameters on laser desorption/ionization from porous alumina

Nanoporous aluminum oxide layers, grown by anodization of aluminum thin films on glass and then sputter-coated with gold, were used to study the effects of the thin-film structural parameters on laser desorption/ionization (LDI) mass spectrometry (MS) of peptides. Variation of MS signal intensity was examined as a function of alumina pore depth, pore width, and gold layer thickness. Peptide molecular ion intensity was optimal with porous alumina formed from aluminum films of ~600-nm thickness; thinner or thicker films gave significantly lower signals. Signals decreased when pore sizes were increased beyond the as-formed width of ~100 nm. The MS signal also varied with the thickness of the sputtered gold layer with an optimum thickness being ~90 nm. The results of these studies provide values for empirical optimization of LDI MS performance as well as potential clues to the LDI mechanism.