1. Department of Biochemistry, Science Institute, University of Iceland, Sturlugata 7, 102 Reykjavík, Iceland
2. Department of Physics, Informatics and Mathematics, University of Modena and Reggio Emilia, Modena 41125, Italy
3. Center S3, CNR Institute Nanoscience, Via Campi 213/A, Modena 41125, Italy