Plasmonic polymers unraveled through single particle spectroscopy

Abstract

Plasmonic polymers are quasi one-dimensional assemblies of nanoparticles whose optical responses are governed by near-field coupling of localized surface plasmons. Through single particle extinction spectroscopy correlated with electron microscopy, we reveal the effect of the composition of the repeat unit, the chain length, and extent of disorder on the energies, intensities, and line shapes of the collective resonances of individual plasmonic polymers constructed from three different sizes of gold nanoparticles. Our combined experiment and theoretical analysis focuses on the superradiant plasmon mode, which results from the most attractive interactions along the nanoparticle chain and yields the lowest energy resonance in the spectrum. This superradiant mode redshifts with increasing chain length until an infinite chain limit, where additional increases in chain length cause negligible change in the energy of the superradiant mode. We find that, among plasmonic polymers of equal width comprising nanoparticles with different sizes, the onset of the infinite chain limit and its associated energy are dictated by the number of repeat units and not the overall length, of the polymer. The intensities and linewidths of the superradiant mode relative to higher energy resonances, however, differ as the size and number of nanoparticles are varied in the plasmonic polymers studied here. These findings provide general guidelines for engineering the energies, intensities, and line shapes of the collective optical response of plasmonic polymers constructed from nanoparticles with sizes ranging from a few tens to one hundred nanometers.

Self-assembled flat-faceted nanoparticles chains as a highly-tunable platform for plasmon-enhanced spectroscopy in the infrared

“…We argue that these results might have direct consequences in more complex branched aggregates [14,61], whose optical response can be dominated by plasmonic modes supported by chain-like subunits.The description of the optical response of aggregates as ensembles of linear chains is based on the validation of this concept for spherical particles, and we expect it to be valid also in clusters formed by flat-faceted units, at least if the different gaps are always formed between well-aligned flat facets. Furthermore, although the inherent disorder found in self-assembled aggregates modifies to some extent the plasmonic modes, the overall properties of the plasmonic response have been found to be quite robust with respect to disorder in previous work [14,32,62,63]. The experimental realization of such 2 or 3-dimensional aggregates would require particles with more than two flat facets.…”

Direct Observation of Plasmon Band Formation and Delocalization in Quasi-Infinite Nanoparticle Chains

“…In contrast to rod like structures, 33 the excitation energy of the L1 mode in long chains converges at low energies, described as the infinite chain limit. 16 In literature, this limit is typically defined somewhere between 8 and 12 particles (see also a spectral visualization in Figure S1). 15,16 In contrast, nanoparticle dipole moments, perpendicular to the chain axis, couple only weakly, resulting in (almost) degenerate transversal modes (marked as T at 2.2 eV/560 nm).…”

Dopamine-Mediated Assembly of Citrate-Capped Plasmonic Nanoparticles into Stable Core–Shell Nanoworms for Intracellular Applications

“…One-dimensional (1D) plasmonic nanochains − are now utilized in numerous plasmon-driven applicatons, − including optical sensing, , catalysis, and energy harvesting. , The plasmonic properties of nanochains resemble those of other anisotropic plasmonic objects such as nanorods (NRs) , and nanowires, exhibiting localized surface plasmon resonance (LSPR) in transverse and longitudinal modes. , Tuning of the LSPR responses of plasmonic nanochains is flexible and supported by their large number of architectural parameters available for adjustment, including shape and composition of nanoparticle (NP) building blocks, number of NPs per chain, and gap distance between adjacent NPs in the chain. ,− To date, few studies have explored the use of plasmonic nanochains for intracellular applications, owing to the limitations of various existing methods of 1D assembly. Dewetting necessitates dispersion of plasmonic NPs in organic solvents and subsequent drying for assembly on solid substrates, − yet it is unclear whether the nanochains retain their morphology upon their transferal to aqueous cell culture medium.…”