Core–satellite–satellite hierarchical nanostructures: assembly, plasmon coupling, and gap-selective surface-enhanced Raman scattering

Abstract

The plasmonic properties of gold nanoparticles (AuNPs), such as color tunability, electric field generation, hot carrier generation, and localized heating, are significantly enhanced in the nanogaps between AuNPs. Therefore, the...

Combinatorial Approach to Find Nanoparticle Assemblies with Maximum Surface-Enhanced Raman Scattering

“…This color change originates from the plasmon coupling between the core and satellite AuNPs across the small nanogap defined by the ABT SAMs and CTA monolayers. The interaction between the dipolar plasmon modes of core and satellite AuNPs leads to a hybridized coupling mode at lower energy and shifts the resonance to longer wavelengths. ,,, This plasmon coupling is clearly observed in the UV–vis spectra (Figure b). While the LSPR peaks of the individual AuNCs occur at 520 and 549 nm, a new peak emerges at longer wavelengths when they form CS nanoassemblies.…”

“…Finally, immersion of the thiol- or amine-functionalized core AuNPs on glass substrates in a solution of satellite AuNPs completes the formation of CS nanoassemblies (Step 5). The satellite AuNPs, including smaller cit-AuNSs or acetonitrile-treated CTA-AuNPs, bind to the core AuNPs through Au–S bond formation or electrostatic interactions. , The adsorption of satellite AuNPs onto the surface of the core nanoparticles follows pseudo-first-order Langmuir adsorption kinetics. The number of satellite AuNPs per core increases with their concentration and the immersion time, until the electrostatic repulsion between the satellite AuNPs begins to take effect and keeps them separated. , …”

Mode-Selective Plasmon Coupling between Au Nanorods and Au Nanospheres

“…16,45−47 Furthermore, the nanogaps are inhomogeneous when the core and satellite nanoparticles are bound by electrostatic interactions. 21,24 The nanogap distances that can be attained using DNA linkers are larger than a few nanometers because of the number of DNA bases required for hybridization and the alkyl spacers for tethering, leading to only weak plasmon coupling. 41,44,48−50 In contrast, our new assembly method is fast, effective, and flexible when compared with previously reported methods.…”

“…Many research groups, including our group, primarily investigated plasmon coupling that occurs between spherical AuNPs (AuNSs). − We assembled AuNSs into dimers, core–satellite nanostructures, − or core–satellite–satellite hierarchical nanostructures in a controlled fashion. Systematic changes in the interparticle distances using molecular linkers and measurements of the consequent plasmon coupling allowed us to gain insight into the nature of plasmon coupling.…”

“…However, it inevitably produces either unbound AuNSs due to the addition of excessive AuNSs or aggregates formed by AuNSs bridging the AuNRs, in addition to the targeted AuNR–AuNS nanoassemblies. In principle, the desired nanoassemblies can be separated from the mixtures using differential centrifugation or electrophoresis, but this lowers the overall throughput of the assemblies. ,− Furthermore, the nanogaps are inhomogeneous when the core and satellite nanoparticles are bound by electrostatic interactions. , The nanogap distances that can be attained using DNA linkers are larger than a few nanometers because of the number of DNA bases required for hybridization and the alkyl spacers for tethering, leading to only weak plasmon coupling. ,,− In contrast, our new assembly method is fast, effective, and flexible when compared with previously reported methods. The entire assembly process takes <5 h. The effective removal of the amine coating from glass substrates through plasma treatment ensures a 100% yield of AuNR@AuNS, with no AuNS monomers left on the glass substrates.…”