Nucleation: theory and applications to protein solutions and colloidal suspensions

The status of our understanding of nucleation is reviewed. Both general aspects of nucleation and those specific to protein solutions and colloidal suspensions are considered. We conclude that although we have what we believe is a quite good understanding of homogeneous nucleation in one simple system, hard-sphere colloids, in other systems there are still basic questions that are unanswered. For example, for even the most studied protein, lysozyme, there is an ongoing debate about whether the observed nucleation is homogeneous or heterogeneous. We review theoretical and simulation work on both homogeneous and heterogeneous nucleation. As heterogeneous nucleation appears to be much more common than homogeneous nucleation, and as earlier reviews have tended to focus more on homogeneous nucleation, we place particular emphasis on heterogeneous nucleation. (topical review)