Self-Assembly of Mesoscopic Peptide Surfactant Fibrils Investigated by STORM Super-Resolution Fluorescence Microscopy

Super-resolution fluorescence microscopy, specifically stochastic reconstruction microscopy (STORM), and atomic force microscopy (AFM) were used to image the self-assembly processes of the peptide surfactant I₃K. The peptide surfactants self-assembled into giant helical fibrils with diameters between 5 and 10 nm with significant helical twisting. The resolution of the STORM images was 30 nm, calculated using the Fourier ring correlation method. STORM compares favorably with AFM for the calculation of contour lengths (∼6 microm) and persistence lengths (10.1 ± 1.2 microm) due to its increased field of view (50 microm), and its ability to image bulk morphologies away from surfaces under ambient solution conditions. Two-color STORM experiments were performed to investigate the dynamic process of self-assembly after mixing of two separately labeled samples, and the results revealed the formation of long nanofibers via end-to-end connections of short ones. No evidence was found for significant monomer exchange between the samples, and the self-assembled structures were very stable and long-lived.