Optimization of Spectral and Spatial Conditions to Improve Super-Resolution Imaging of Plasmonic Nanoparticles.

Interactions between fluorophores and plasmonic nanoparticles modify the fluorescence intensity, shape, and position of the observed emission pattern, thus inhibiting efforts to optically super-resolve plasmonic nanoparticles. Herein, we investigate the accuracy of localizing dye fluorescence as a function of the spectral and spatial separations between fluorophores (Alexa 647) and gold nanorods (NRs). The distance at which Alexa 647 interacts with NRs is varied by layer-by-layer polyelectrolyte deposition while the spectral separation is tuned by using NRs with varying localized surface plasmon resonance (LSPR) maxima.

Single-Molecule Kinetics of Protein Adsorption on Thin Nylon-6,6 Films.

Understanding and controlling protein adsorption on surfaces is critical to a range of biological and materials applications. Kinetic details that provide the equilibrium and nonequilibrium mechanisms are difficult to acquire. In this work, single-molecule fluorescence microscopy was used to study the adsorption of Alexa 555 labeled α-lactalbumin (α-LA) on two chemically identical but morphologically different polymer surfaces: flat and porous nylon-6,6 thin films.

Absorption Spectroscopy of an Individual Fano Cluster.

Plasmonic clusters can exhibit Fano resonances with unique and tunable asymmetric line shapes, which arise due to the coupling of bright and dark plasmon modes within each multiparticle structure. These structures are capable of generating remarkably large local electromagnetic field enhancements and should give rise to high hot carrier yields relative to other plasmonic nanostructures. While the scattering properties of individual plasmonic Fano resonances have been characterized extensively both experimentally and theoretically, their absorption properties, critical for hot carrier generation, have not yet been measured.

Adsorption and Unfolding of a Single Protein Triggers Nanoparticle Aggregation.

The response of living systems to nanoparticles is thought to depend on the protein corona, which forms shortly after exposure to physiological fluids and which is linked to a wide array of pathophysiologies. A mechanistic understanding of the dynamic interaction between proteins and nanoparticles and thus the biological fate of nanoparticles and associated proteins is, however, often missing mainly due to the inadequacies in current ensemble experimental approaches. Through the application of a variety of single molecule and single particle spectroscopic techniques in combination with ensemble level characterization tools, we identified different interaction pathways between gold nanorods and bovine serum albumin depending on the protein concentration.

From tunable core-shell nanoparticles to plasmonic drawbridges: Active control of nanoparticle optical properties.

The optical properties of metallic nanoparticles are highly sensitive to interparticle distance, giving rise to dramatic but frequently irreversible color changes. By electrochemical modification of individual nanoparticles and nanoparticle pairs, we induced equally dramatic, yet reversible, changes in their optical properties. We achieved plasmon tuning by oxidation-reduction chemistry of Ag-AgCl shells on the surfaces of both individual and strongly coupled Au nanoparticle pairs, resulting in extreme but reversible changes in scattering line shape.

Photoluminescence of a Plasmonic Molecule.

Photoluminescent Au nanoparticles are appealing for biosensing and bioimaging applications because of their non-photobleaching and non-photoblinking emission. The mechanism of one-photon photoluminescence from plasmonic nanostructures is still heavily debated though. Here, we report on the one-photon photoluminescence of strongly coupled 50 nm Au nanosphere dimers, the simplest plasmonic molecule.

Single-particle absorption spectroscopy by photothermal contrast.

Removing effects of sample heterogeneity through single-molecule and single-particle techniques has advanced many fields. While background free luminescence and scattering spectroscopy is widely used, recording the absorption spectrum only is rather difficult. Here we present an approach capable of recording pure absorption spectra of individual nanostructures.

Optical characterization of single plasmonic nanoparticles.

This tutorial review surveys the optical properties of plasmonic nanoparticles studied by various single particle spectroscopy techniques. The surface plasmon resonance of metallic nanoparticles depends sensitively on the nanoparticle geometry and its environment, with even relatively minor deviations causing significant changes in the optical spectrum. Because for chemically prepared nanoparticles a distribution of their size and shape is inherent, ensemble spectra of such samples are inhomogeneously broadened, hiding the properties of the individual nanoparticles.

Using the plasmon linewidth to calculate the time and efficiency of electron transfer between gold nanorods and graphene.

We present a quantitative analysis of the electron transfer between single gold nanorods and monolayer graphene under no electrical bias. Using single-particle dark-field scattering and photoluminescence spectroscopy to access the homogeneous linewidth, we observe broadening of the surface plasmon resonance for gold nanorods on graphene compared to nanorods on a quartz substrate. Because of the absence of spectral plasmon shifts, dielectric interactions between the gold nanorods and graphene are not important and we instead assign the plasmon damping to charge transfer between plasmon-generated hot electrons and the graphene that acts as an efficient acceptor.