* Corresponding authors

^a Laboratory of Physical Chemistry and Electrochemistry, Helsinki University of Technology, P.O. Box 6100, HUT, Finland
E-mail: kontturi@cc.fi
Fax: +358 9 451 2580
Tel: +358 9 451 2572

^b Division of Pharmaceutical Technology, Faculty of Pharmacy, University of Helsinki, P.O. Box 56, Finland
E-mail: timo.laaksonen@helsinki.fi
Fax: +358 9 191 59144
Tel: +358 9 191 59161

^c Centre for Nanoscale Science, Chemistry Department, University of Liverpool, United Kingdom
E-mail: schiffrn@liv.ac.uk
Fax: +44 151 794 3588
Tel: +44 151 794 3574