Acting in a vast variety of functions, proteins play a crucial role in living organisms. As failure to fold into the precise shape intended can result in protein-based diseases, understanding the mechanism of folding is essential to finding treatments for these diseases and to designing novel proteins for pharmacological and biotechnological applications.

Modern theories and recent experiments indicate that proteins may take multiple pathways during folding; as a result, new techniques are needed in order to tackle this heterogeneity. In this regard, single-molecule fluorescence is a...