Shape and Size Control of Substrate-Grown Gold Nanoparticles for Surface-Enhanced Raman Spectroscopy Detection of Chemical Analytes

Anisotropic gold nanoparticles often exhibit superior optical properties compared to spherical ones, in part due to intense electric field localization near sharp geometric features and a broadly tunable localized surface plasmon resonance. As a result, anisotropic nanoparticles are attractive building blocks for surface-enhanced Raman spectroscopy (SERS) substrates. To unlock the full potential of such substrates, one should be able to (1) generate a sufficient number of SERS hotspots with structures of controlled shape and size and (2) remove ligands so that analytes can easily access nanoparticle surface sites. Here, we develop a synthetic strategy for the shape- and size-controlled anisotropic growth of gold nanoparticles (concave rhombic dodecahedra and concave cubes, 70-135 nm characteristic length) from spherical seeds anchored on a structurally complex surface (common filter paper) and subsequently combine electrodynamics and electronic structure calculations with experiment to systematically characterize these substrates using SERS. Furthermore, we explore the generalizable functionality of these substrate-stabilized nanoparticles by using a continuous extraction method to partially remove surface ligands that were necessary for anisotropic growth, enabling the specific SERS detection of serotonin, a molecular neurotransmitter with a weak affinity for gold.