We present a study of the dynamics of protein aggregation using a common path heterodyne Bloch surface wave sensing scheme. We demonstrate the ability to detect, during thermal incubation, the early events linked to the aggregation of proteins related to conformational diseases. Alzheimer's amyloid-β 1-42 is used to demonstrate the efficiency of the method. A model based on elementary interactions is shown to describe accurately the aggregation process. The described sensing scheme is sensitive to the early events of the aggregation process. is hence proposed as a method for the detection of early stages of the evolution of conformational diseases