1. Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6703 HB Wageningen, The Netherlands
2. Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands
3. MicroSpectroscopy Centre, P.O. Box 8128, 6700 ET Wageningen, The Netherlands