Peptide mesocrystals as templates to create an Au surface with stronger surface-enhanced Raman spectroscopic properties.

The design and fabrication of various nanostructures with predefined geometry and composition is a big challenge of nanotechnology. Here we demonstrate an Au nanoflake film replicated from a self-assembled, well-ordered, dipeptide flower-like hierarchical architecture. Such morphology can give rise to useful and remarkable surface-enhanced Raman spectroscopy (SERS) properties. We obtained these nanostructures by using a scaffold of flake-built spherical dipeptide aggregations. Gold nanoparticles were sputtered on the surface of as-assembled dipeptide by an etching system. After removing the dipeptide templates by ethanol, a metal crust was left with a morphology similar to that of the dipeptide hierarchical structure. The different steps within the process were monitored by using electron microscopy, energy-dispersive spectrum (EDS) analysis and atomic force microscopy (AFM). Cyclic voltammetry and Raman spectra were employed to prove the SERS effect of the obtained Au substrates. The enhancement factor is estimated to be about 10(4) for 4-mercaptobenzoic acid (4-MBA) molecules on the Au nanoflake surfaces.