Screening crystallisation conditions using fluorescence correlation spectroscopy.

We investigate the potential of fluorescence correlation spectroscopy (FCS) in screening for crystallisation conditions. Solutions that nucleate protein crystals must have different interactions than solutions that do not give rise to crystals. Due to these different interactions the average mean squared displacement of the individual proteins changes. By monitoring protein self-diffusion, we can distinguish crystallizing from non-crystallizing solutions. The method introduced can be applied at extremely low concentrations in femtoliter volumes as an early diagnostic for molecular association. Based on our preliminary findings FCS has the potential to become a routine screening method for crystallography.