1. Department of Physics, University of Gothenburg, Origovägen 6B, 412 96 Göteborg, Sweden
2. Department of Chemical Engineering and Materials Science, University of Minnesota–Twin Cities, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, USA
3. Department of Biology and Biological Engineering, Chalmers University of Technology, 412 96 Göteborg, Sweden
4. Department of Physics, Chalmers University of Technology, 412 96 Göteborg, Sweden