Scanning electron microscopy imaging of insulin amyloid fibrils directly grown on silicon substrate: a suggestion for complementary imaging strategy

Abstract

A new visualization method of insulin amyloid fibril has been presented via conventional scanning electron microscopy (SEM), which can be applied to confirm the fibril formation and any effect of additives. We have demonstrated that native insulin amyloid fibrils can be imaged without any metal coating on the silicon substrate and were attributed to the attenuation effect upon the collected secondary electrons. The conventional SEM observations consistently showed distinct morphologies of the fibrils under the effects of three different molecules (citrulline, ectoin, and trehalose) and well coincident with atomic force microscopic (AFM) data. In spite of negative result for trehalose-treated samples with conventional thioflavin T (Th-T) assay, thin and long fibrils were thoroughly observed and it revealed a complementary capability of the present strategy. In addition, direct sampling of amyloid fibrils on silicon chips for SEM observations substantially expedites the sampling and searching efforts, thereby shedding a new light on inhibitor screening approach for diverse amyloid fibrillation.