New Light on Like-Charge Attraction
  We report on pair interaction measurements in charged colloidal systems in confined and unconfined geometries by means of optical microscopy. At very small particle distances we observe minute distortions in the optical images which can lead to artifacts in the pair potentials as derived by digital video microscopy. In particular, these distortions can pretend long-range attractions observed in charged colloidal suspensions. 
Joerg Baumgartl, Jose Luis Arauz-Lara, and Clemens Bechinger