1. National Research Council (CNR) Institute of Neuroscience , Pisa 56124 , Italy
2. Bio@SNS laboratory, Scuola Normale Superiore , Pisa 56124 , Italy
3. National Research Council (CNR) Institute of Neuroscience, Vedano al Lambro , Monza (MB) 20854 , Italy
4. National Enterprise for nanoScience and nanoTechnology (NEST), Istituto Nanoscienze, Consiglio Nazionale delle Ricerche (CNR) and Scuola Normale Superiore Pisa , Pisa 56127 , Italy
5. Department of Pathology and Cell Biology, The Taub Institute for Research on Alzheimer’s Disease and the Aging Brain and Department of Medicine, Columbia University , New York, NY 10032 , USA