Fluorescent nanofibrils constructed by self-assembly of a peptide amphiphile with an anionic dye

The interaction between a peptide amphiphile C(12)-A beta(11-17) and an anionic dye TPE with aggregation-induced emission (AIE) feature at different pH has been studied. C(12)-A beta(11-17) was constructed by attaching a key fragment of amyloid beta-peptide (A beta(11-17)) to a dodecanoic acid through an amide bond. It was found that highly fluorescent nanofibrils can be constructed through the self-assembly of C(12)-A beta(11-17) with TPE. Moreover, formation, structure and fluorescence intensity of the nanofibrils can be modulated by changing pH and the concentration of C(12)-A beta(11-17). In the solution of 0.05 mM C(12)-A beta(11-17) and 0.05 mM TPE, as the pH decreases, the fluorescence intensity of the mixed solution is invariable at pH > 7.0, then fast increases to the maximum while 4.0 < pH < 7.0, and finally fast decreases at pH < 4.0. Only at pH 4.0-7.0, fluorescent nanofibrils of less than 5 mu m length with the beta-sheet secondary structure are formed upon the addition of TPE molecules. In 1.0mM C(12)-A beta(11-17) solution with 0.05 mM TPE, the fluorescence intensity of the mixed solution keeps increasing as the pH decreases in the pH range of 3.4-11.0, and the mixture forms strongly fluorescent nanotapes of more than 50 mu m length with an ordered beta-sheet structure at pH 3.0 or relatively weaker fluorescent nanoribbons with a random coil structure at pH 10.0.