High-Concentration Multibranched Gold Nanoparticle Synthesis via Controllable Seeding

Engineering gold nanostructures with a high number of sharp branches allows harvesting near-infrared light-induced localized surface plasmon resonance (LSPR) effects in which free electrons are brought into oscillation with exceptional electromagnetic field enhancement at the branch tips of these particles. These tip effects make such particles promising candidates for biological, catalytic, and spectroscopic applications. In this work, a scale-up process for highly multibranched gold nanoparticles at high concentrations (2.95 mM postsynthesis gold nanoparticle concentration, 95% yield) based on seeded-fragment self-assembly is introduced. First, a novel sodium borohydride-free synthesis method of gold nanoseeds was developed and demonstrated at a synthesis scale-up at 1 order of magnitude higher concentration than previously reported. Subsequently, oleate as a stabilizing agent was leveraged for the high-concentration seeded synthesis of multibranched gold nanoparticles with high LSPR reproducibility and LSPR peak position tuning over a wide range (780-1140 nm), and synthesis scaleup was demonstrated at up to 0.1 g Au per batch. A systematic evaluation of seed type and seed amount indicates an intermediary growth step entailing the development of anisotropic fragments prior to an aggregative growth step of fragments into spherical, multibranched gold nanoparticles. Particles obtained from the proposed method are compatible with common postsynthesis modification of multibranched gold nanoparticles, demonstrated through capping agent exchange and surface-enhanced Raman spectroscopy (SERS) sensor capability.