Coumarin 6 (Coumarin VI) is a fluorescent dye frequently used to facilitate the traceability of drug delivery systems in vitro.

We report the use of Coumarin 6(Coumarin VI) and 1,6-diphenyl-1,3,5-hexatriene (DPH) for the identification of protein aggregates for the first time. The two dyes can be used at very low (nanomolar) concentrations and do not interfere with the aggregation process, as is reported for other commonly used fluorescent protein probes. In the presence of protein aggregates, their quantum yields are significantly high. DPH is able to recognize both amorphous and fibrillar aggregates but cannot distinguish between them. Coumarin 6(Coumarin VI) can distinguish between both types of aggregates. It also exhibits the characteristic sigmoidal curve of amyloid formation, with higher sensitivity for detection of fibrillation than the conventionally used Thioflavin T.