Light-Directed Patchy Particle Fabrication and Assembly from Isotropic Silver Nanoparticles.

Abstract

We demonstrate the creation of anisotropic patchy silver nanospheroids (AgNSs) using linearly polarized UV light and a photo-uncaging o-nitrobenzyl-based ligand, which anchors to the AgNSs by two gold-sulfur bonds. Exposure to a 1 J/cm2 dose of UV light induces a photo-uncaging reaction in the ligand that reveals a primary amine on the surface. By using linearly polarized UV light, we meter the exposure dose such that only the poles of the nanoparticle receive a full dose, limiting the photo-uncaging reaction primarily to the particle's plasmonic hot spots. We reveal this anisotropy by preferentially adhering negatively charged gold nanospheres (AuNSs) to the AgNSs' poles by using the electrostatic attraction between them and the positively charged primary amines generated by photo-uncaging. When the assembly is performed onto silver particles that are immobilized on a substrate, it results in nanoscale structures with a strong tendency to align with the polarization of the exposing light. This manifests in polarimetric spectroscopy as a linear dichroism aligned with the polarization direction.