1. Institute of Robotics and Intelligent Systems; ETH Zurich; Zurich CH-8092 Switzerland
2. Wyss Institute for Biologically Inspired Engineering; School of Engineering and Applied Sciences; Harvard University; Cambridge MA 02318 USA
3. Micro and Nanosystems; ETH Zurich; Zurich CH-8092 Switzerland
4. Particle Technology Laboratory; ETH Zurich; Zurich CH-8092 Switzerland
5. Center for Nanotechnology & Nanotoxicology; Harvard School of Public Health; Boston MA 02115 USA