1. Nanotechnology Lab.; National Council of the Research; CNR-ISTM; Via G. Fantoli 16/15 20138 Milan Italy
2. Department of Chemistry; University of Milan; Via C. Golgi 19 20133 Milan Italy
3. Present address: Department of Biomaterials; Max-Planck Institute of Colloids and Interfaces; Potsdam-Golm 14476 Germany
4. CRC Materiali Polimerici (LaMPo); University of Milan; Via C. Golgi 19 20133 Milan Italy