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

Abstract

The interaction between a peptide amphiphile C₁₂–Aβ(11–17) and an anionic dye TPE with aggregation-induced emission (AIE) feature at different pH has been studied. C₁₂–Aβ(11–17) was constructed by attaching a key fragment of amyloid β-peptide (Aβ(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 C₁₂–Aβ(11–17) with TPE. Moreover, formation, structure and fluorescence intensity of the nanofibrils can be modulated by changing pH and the concentration of C₁₂–Aβ(11–17). In the solution of 0.05 mM C₁₂–Aβ(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 μm length with the β-sheet secondary structure are formed upon the addition of TPE molecules. In 1.0 mM C₁₂–Aβ(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 μm length with an ordered β-sheet structure at pH 3.0 or relatively weaker fluorescent nanoribbons with a random coil structure at pH 10.0.