Super-resolution imaging of single-molecule DNA interactions with plasmonic nanoparticles

Introduction: Plasmonic nanoparticle-sensors are widely employed to detect analyte binding to receptors on the surface of the particle. The response of a plasmonic sensor strongly depends on the position where an analyte... [ view full abstract ]

Introduction:

Plasmonic nanoparticle-sensors are widely employed to detect analyte binding to receptors on the surface of the particle. The response of a plasmonic sensor strongly depends on the position where an analyte binds due to the spatially heterogeneous near-field. Also, binding kinetics are expected to vary across a nanoparticle surface due to geometry dependent fluid accessibility. It however remains unknown how the location of binding of an analyte correlates with binding kinetics and sensor response.

Method:

Here we employ super-resolution microscopy to establish the location of analyte binding at the single molecule, single-particle level. We use a fluorophore-coupled oligo, which transiently binds to an oligo functionalized gold bipyramid (Fig 1, top) via DNA hybridization. To prevent near-field coupling between the fluorophore and the plasmon resonance we employ a dye (ATTO532, λ_emission = 540 nm) that is spectrally detuned far away from the longitudinal plasmon wavelength (λ_LSPR = 815nm).

Results:

A resulting time trace showing fluorescence bursts from DNA hybridization events on the surface of a single bipyramid is shown in Figure 1 (middle). Each event is localized, with centroids plotted in Figure 1 as red dots (bottom). The geometry and orientation angle of the underlying nanoparticle is reconstructed by fitting an ellipse to the distribution of localisation coordinates, finding close agreement to dimensions obtained from TEM (~ 110 nm x ~ 40 nm as measured by TEM).

Discussion:

Our approach provides an all-optical method to reconstruct particle geometry. In addition, the localization of each binding event will enable us to establish the connection between binding location, binding kinetics, and sensor response at the single-molecule level. This will further our understanding of nanoparticle-based biosensors and give insight into geometry-dependent interaction kinetics.