Daniel J Müller1, Hermann E Gaub2. 1. Department of Biosystems Science and Engineering, ETH Zürich, 4058 Basel, Switzerland. daniel.mueller@bsse.ethz.ch gaub@lmu.de. 2. Department of Physics, Ludwig-Maximilians-Universität, 80799 München, Germany. daniel.mueller@bsse.ethz.ch gaub@lmu.de.