Peptide-Directed Hierarchical Plasmonic Biomaterials via Diffusion-Limited Aggregation: The Impact of Surface Chemistry

Diffusion-limited aggregation (DLA) of nanoparticles provides a powerful model for studying hierarchical assembly. This study reveals how specific ligand chemistries catalyze or constrain the aggregation dynamics of peptide-driven DLA using silver nanoparticles (AgNPs) as a platform. We first functionalized AgNPs with nine ligands—phosphines, thiolates, and polyphenols— chosen for their unique interactions with metal surfaces and impact on stability and reactivity. Our aim is to pinpoint which ligands best promote fractal structure formation, providing fresh insights into the deliberate design of nanoparticles. By analyzing ligand charge, functional group, and binding affinity we uncover the mechanistic factors that drive fractal growth, oxidation dynamics, and structural stability. Comprehensive spectroscopic and microscopic analyses reveal that aromatic phosphine ligands—particularly bis(p-sulfonatophenyl)phenylphosphine (BSPP)— uniquely promote fractal assembly, whereas thiol- and polyphenol-based ligands primarily lead to non-fractal aggregates. This trend is likely due to an optimal balance of electrostatic stabilization and controlled ligand desorption. In contrast, thiol and polyphenol ligands either bind too strongly, preventing the necessary ligand displacement for fractal assembly, or lack the electronic and steric properties required to modulate oxidation dynamics. Our data confirm this mechanism: X- ray photoelectron spectroscopy detects oxidized silver species in BSPP-Ag fractals, zeta- potential measurements indicate charge neutralization, and small-angle X-ray scattering shows increased light scattering of BSPP-AgNPs, suggesting surface heterogeneity. Electron microscopy and elemental analyses further validate the architecture and its composition. By leveraging ligand engineering to control self-assembly, this work provides a versatile strategy for designing hierarchical nanomaterials with applications in biosensing, catalysis, and functional nanostructures.