1. Department of Biochemistry and Molecular Biology, University of Parma, Viale Usberti 23 A, 43100 Parma, Italy, Department of Physics, University of Parma, Viale Usberti 7 A, 43100 Parma, Italy, LAMBS-MicroSCoBiO Research Center, Department of Physics, University of Genoa, Via Dodecaneso 33, 16146, Italy, and CRS SOFT CNR-INFM, Rome 00185, Italy