Understanding Time-Dependent Surface-Enhanced Raman Scattering from Gold Nanosphere Aggregates Using Collision Theory

Abstract

Aggregates or clusters of primary metal nanoparticles in solution are one of the most widely used platforms for surface-enhanced Raman scattering (SERS) measurements because these nanostructures induce strong electric fields or hot spots between nanoparticles and as a result, SERS signals. While SERS signals are observed to vary with time, the impact of cluster formation mechanisms on SERS activity has been less studied. Herein, variations in time-dependent SERS signals from gold nanosphere clusters and aggregates are considered both experimentally and theoretically. An excess of the Raman reporter molecule, 2-naphthalenethiol, is added to induce rapid monolayer formation on the nanoparticles. In this diffusion-limited regime, clusters form as loosely packed fractals and the ligands help control nanoparticle separation distances once clusters form. By systematically varying gold nanosphere concentration and diameter, the reaction kinetics and dynamics associated with cluster formation can be studied. Dynamic light scattering (DLS), localized surface plasmon resonance (LSPR) spectroscopy, and SERS reveal that aggregates form reproducibly in the diffusion-limited regime and follow a self-limiting cluster size model. The rate of cluster formation during this same reaction window is explained using interaction pair potential calculations and collision theory. Diffusion-limited reaction conditions are limited by sedimentation only if sedimentation velocities exceed diffusion velocities of the clusters or via plasmon damping through radiation or scattering losses. These radiative loses are only significant when the extinction magnitude near the excitation wavelength exceeds 1.5. By evaluating these responses as a function of both nanosphere radius and concentration, time-dependent SERS signals are revealed to follow collision theory and be predictable when both nanosphere concentration and size are considered.

Gold Nanostar Spatial Distribution Impacts the Surface-Enhanced Raman Scattering Detection of Uranyl on Amidoximated Polymers

“…The LSPR spectra for gold nanostars deposited on the polymer films do not correlate to the hybridized optical properties associated with Au nanostar core and branches. 34 Instead, the broad feature observed is consistent with scattering, which arises from both gold nanostar multilayers 13 and the electrospun polymer fibers. 35,36 While the LSPR feature is broad, variations in this band can be quantified spatially by determining the full width at halfmaximum (Γ) via raster scanning the substrate.…”

“…2,5−7 The electric fields that extend from the nanostar surfaces arise from the LSPR, which leads to electromagnetically enhanced Raman signals for molecules in these fields. 8,9 LSPR spectral features vary with nanoparticle composition, 10−12 shape, 2,10 and size; 13,14 so SERS enhancements also depend on these same parameters. In addition to solution-phase measurements, gold nanostars have been deposited onto polymers, 15,16 glass, 17 and paper 18,19 for sensor development, but the surface roughness and chemistry of these substrates often influence the optical properties 16,19 and spatial distribution 17,18 of gold nanostars, thereby limiting quantitative molecular detection.…”

Giant Second Harmonic Generation Enhancement by Ag Nanoparticles Compactly Distributed on Hexagonal Arrangements

“…Such a large enhancement is achieved by taking advantage of the strong near field generated at the metal-dielectric interface associated The much larger enhancement in the small hexagons could be related to the existence of extended collective plasmonic modes propagating through the entire hexagon. In fact, the possibility of using the inner NP structure as plasmonic interconnection between the different sides of the hexagon could also favor the propagation of the plasmon mode inside the hexagon [47][48][49][50][51]. Additionally, due to the hexagon dimensions, the presence of modes in the wavelength-scale hexagonal nanocavity could also contribute to the light confinement and enhanced light-matter interaction process [52].…”

One-Pot Synthesis of a Three-Dimensional Au-Decorated Cellulose Nanocomposite as a Surface-Enhanced Raman Scattering Sensor for Selective Detection and in Situ Monitoring

“…There are several general reasons for the unique properties exhibited by Au NPs. For instance, the activity of gold displays a direct relationship to the particle size . Thus, numerous works focused on the synthesizing strategy of Au NPs.…”

“…For instance, the activity of gold displays a direct relationship to the particle size. 10 Thus, numerous works focused on the synthesizing strategy of Au NPs. Under such a context, Tween 80 was used as the dispersant to construct Au NPs in a controlled manner.…”