Structured and oriented immobilization of bio-molecules has become subject of great interest in recent years due to the expected diversity of applications, e.g. bio sensors in diagnosis, lab-on-chip technology, and modern cell culture focused on cell adhesion, migration, and differentiation. Therefore, a lot of effort has been spent to develop strategies for covalent and non-covalent immobilization of proteins, respectively. A very promising approach is surface patterning by micro-contact printing (µCP) to produce self-assembled-monolayers (SAMs) on gold surfaces based on mixtures of benzylguanine thiol (BGT) and matrix thiol. In this case BGT is the substrate for the SNAP-tag system, allowing for covalent attachment of any protein of interest fused to this tag, whereas the inert matrix thiol acts as spacer for BGT and moreover prevents from non-specific protein adsorption.1

The present contribution focuses on the characterization of pure benzylguanine and matrix thiols as well as mixtures of both using a combination of complementary surface analytical methods. For this purpose all SAMs were prepared on gold films deposited onto glass substrates by r. f. magnetron sputtering directly prior to the thiol exposure. The chemical composition and the covalent binding of the thiols were proved by time-of-flight secondary ion mass spectrometry (ToFSIMS) and X-ray photoelectron spectroscopy (XPS) as well. The orientation of the SAMs together with thickness information were achieved by high-sensitive low-energy ion scattering (LEIS),2and were justified by non-destructive depth profiles reconstructed from parallel angle-resolved XPS data applying a maximum entropy algorithm. Finally the µCP micro-structures were verified by ToFSIMS.