Manipulating Acoustic and Plasmonic Modes in Gold Nanostars

TL;DR

This paper reports experimental evidence of plasmonic and acoustic modes in gold nanostars, demonstrating their potential for enhanced molecular detection through localized surface plasmon resonances and stimulated dark modes.

Contribution

It provides the first experimental observation and detailed analysis of both plasmonic edge modes and acoustic breathing modes in gold nanostars, supported by numerical simulations.

Findings

Identification of localized surface plasmon resonances in AuNS

Observation of acoustic breathing modes via EELS

Potential for enhanced biomolecular detection using nanostars

Abstract

In this contribution experimental evidence of plasmonic edge modes and breathing acoustic modes in gold nanostars (AuNS) is reported. AuNS are synthesized in a surfactant-free, one-step wet-chemistry method. Optical extinction measurements of AuNS confirm the presence of localized surface plasmon resonances (LSPRs), while electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) shows the spatial distribution of LSPRs and reveals the presence of acoustic breathing modes. Plasmonic hot-spots generated at the pinnacle of the sharp spikes, due to the optically active edge dipolar mode, allow significant intensity enhancement of local fields, hot-electron injection, and thus useful for size detection of small protein molecules. The breathing modes observed away from the apices of the nanostars are identified as stimulated dark modes - they have an acoustic nature - and likely originate from the confinement of the surface plasmon by the geometrical boundaries of a nanostructure. The presence of both types of modes is verified by numerical simulations. Both these modes offer the possibility to design nanoplasmonic antenna based on AuNS, which can provide information both on mass and polarizability of biomolecules using a two-step molecular detection process.