Surface-assisted assembly of an ionic-complementary peptide: Controllable growth of nanofibers

Numerous studies have shown that a surface can direct and regulate molecular assembly. In this study, the nanofiber growth of an ionic-complementary peptide, EAK16-II, on a mica surface was investigated under various solution conditions via in situ atomic force microscopy. In comparison to the assembly in bulk solution, nanofiber growth of EAK16-II on mica is surface-assisted and involves two steps: (1) adsorption of nanofibers and fiber clusters (from the bulk solution) on the surface, serving as the seeds; (2) fiber elongation of the seeds from their active ends. The nanofiber growth can be controlled by adjusting the solution pH since it modulates the adsorption of the seeds on mica and their growth rates. The amount of the adsorbed seeds decreases with increasing solution pH, while the growth rate under different solution conditions is found to follow the order pure water > 1 mM HCl > I mM NaOH > 10 mM HCl; 10 mM NaOH approximate to 0. The pH-dependent nanofiber growth is due to the surface charge of the peptides and pepticle assemblies in various solutions as indicated by xi-potential measurements. A simple model was proposed to describe surface-assisted nanofiber growth. This study provides insights into the assembly of peptide/protein on a surface, which is essential to understand such physiological protein aggregation systems as amyloid fibrillogenesis. In addition, the potential of this finding to construct biocompatible electrodes for biomolecular sensing is also discussed.