Interaction of nanoparticles with biological systems.

I feel very much honored that I was invited to contribute to a special issue for you, Heiri, in the prestigious Journal Colloids and Surfaces B: Biointerfaces. Moreover, it is with great pleasure that I add a few pages on the topic I was involved with during my active research time, i.e. on the interaction of nanoparticles with biological systems, for this special issue. The research topic continued somehow into the time of my retirement, but with a broader view of nanoparticles, with my engagement in the National Research Program 64 on "Opportunities and Risks of Nanomaterials" of the Swiss National Science Foundation. It was wonderful having you as a world expert on physical-chemical aspects of nanomaterials (powders) in the Steering Committee. Your competence in this field of research work as well as your engagement have always been highly appreciated.