Abstract
In this topic transition of the molecular conformation in ultrathin fibroin films induced by thermal treatment is explained. Bombyx mori silk fibroin was fixed on mica substrates by cast of aqueous fibroin solutions and the microscopic morphologies of the samples were revealed with the atomic force microscope. Optimizing the method to prepare the solution we successfully formed two dimensional thin films in which a network of fibroin molecules developed over the substrate. The film consisted of fibroin molecules in the random coil structure. After the thermal treatments, which are known to convert the secondary structure of fibroin from the random coil to the β-sheet type, the network morphology disappeared and characteristic island-like morphologies appeared. Tendency of formation of β-sheet crystals was confirmed by the fact that the fibroin solution temporally evolved the gel state. Based on these results it was concluded that the islands consist of β-sheet crystals. Of particular interest is the observation that all of the islands had a common thickness value of 1.3 nm. In an overview of related research mica-protein interactions frequently result in characteristic morphology or self-organized patterns of protein aggregates. Such specific interactions between the mica substrates and the fibroin are suggested in the present study.
https://ror.org/00965ax52 
