1 Fibre and Polymer Technology, KTH Royal Institute of Technology, 100 44, Stockholm, Sweden.
2 Department of Micro and Nanosystems, KTH Royal Institute of Technology, 10044, Stockholm, Sweden.
3 Swedish Medical Nanoscience Center, Department of Neuroscience, Karolinska Institute, 17177, Stockholm, Sweden.
4 Department of Physics, Chemistry and Biology, Linköping University, Linköping, SE-581 83, Sweden.
5 Department of Materials Science and Engineering, Henry Samueli School of Engineering and Applied Science, University of California Los Angeles, Los Angeles, CA, 90095, USA.