Nanostructured indium tin oxide slides for small-molecule profiling and imaging mass spectrometry of metabolites by surface-assisted laser desorption ionization MS.

Due to their electrical conductivity and optical transparency, slides coated with a thin layer of indium tin oxide (ITO) are the standard substrate for protein imaging mass spectrometry on tissue samples by MALDI-TOF MS. We have now studied the rf magnetron sputtering deposition parameters to prepare ITO thin films on glass substrates with the required nanometric surface structure for their use in the matrix-free imaging of metabolites and small-molecule drugs, without affecting the transparency required for classical histology. The custom-made surfaces were characterized by atomic force microscopy, scanning electron microscopy, ellipsometry, UV, and laser desorption ionization MS (LDI-MS) and employed for the LDI-MS-based analysis of glycans and druglike molecules, the quantification of lactose in milk by isotopic dilution, and metabolite imaging on mouse brain tissue samples.