1. Department of Physical Chemistry; University of P.J. Šafárik in Košice; Moyzesova 11 040 01 Košice Slovakia
2. Catalan Institute of Nanoscience and Nanotechnology (ICN2) Campus UAB; E-08193 Bellaterra Barcelona Spain
3. Institute of Physics; University of P.J. Šafárik in Košice; Park Angelinum 9 040 01 Košice Slovakia
4. Faculty of medicine; University of P.J. Šafárik in Košice; Trieda SNP 1 040 01 Košice Slovakia