Sequential Growth of Quantized Peptide Brushes on Colloidal Gold

We synthesized rigid, macromolecular brushes with well-defined and quantized brush lengths on a gold nanoparticle substrate by using a macromolecular "grafting from" approach. The macromonomers used in these brushes were thiol- and maleimide-functionalized peptide coiled coil "bundlemers" that fold into discrete 4 nm × 2 nm (length × diameter) cylindrical nanoparticles. With each added peptide macromonomer layer, brush thickness increased by approximately the length of a single bundlemer nanoparticle. Due to the quantized nature of these brushes, we were able to determine grafting density and brush thickness through a simplified local surface plasmon resonance model (LSPR). The accuracy of this model is validated by dynamic light scattering (DLS) and cryo-transmission electron microscopy (cryoTEM). The high grafting density and precise brush thickness, demonstrated by the sequential macromolecular growth of these brushes, could lead to the development of better multifunctional LSPR-based biosensors. Additionally, the LSPR model developed in this paper could be modified to describe other peptides and proteins and could prove to be a valuable tool for characterizing protein adsorption on metallic nanoparticles.