Solvent-Assisted Self-Assembly of Gold Nanorods into Hierarchically Organized Plasmonic Mesostructures

Plasmonic supercrystals and periodically structured arrays comprise a class of materials with unique optical properties that result from the interplay of plasmon resonances, as well as near-and far-field coupling. Controlled synthesis of such hierarchical structures remains a fundamental challenge, as it demands strict control over the assembly morphology, array size, lateral spacing, and macroscale homogeneity. Current fabrication approaches involve complicated multistep procedures lacking scalability and reproducibility, which has hindered the practical application of plasmonic supercrystal arrays. Herein, these challenges are addressed by adding an organic solvent to achieve kinetic control over the template-assisted colloidal assembly of nanoparticles from aqueous dispersion. This method yields highly regular periodic arrays, with feature sizes ranging from less than 200 nm up to tens of microns. A combined experimental/computational approach reveals that the underlying mechanism is a combination of the removal of interfacial surfactant micelles from the particle interface and altered capillary flows. Assessing the efficacy of such square arrays for surface-enhanced Raman scattering spectroscopy, we find that a decrease of the lattice periodicity from 750 nm down to 400 nm boosts the signal by more than an order of magnitude, thereby enabling sensitive detection of analytes, such as the bacterial quorum sensing molecule pyocyanin, even in complex biological media.