Exploring Rotational Diffusion with Plasmonic Coupling

ACS Photonics, vol. 11, pp. 634–641

Abstract

High Resolution Image Download MS PowerPoint Slide Measuring the orientation dynamics of nanoparticles and nonfluorescent molecules in real time with optical methods is still a challenge in nanoscience and biochemistry. Here, we examine optoplasmonic sensing taking the rotational diffusion of plasmonic nanorods as an experimental model. Our detection method is based on monitoring the dark-field scattering of a relatively large sensor gold nanorod (GNR) (40 nm in diameter and 112 nm in length) as smaller plasmonic nanorods cross its near field. We observe the rotational motion of single small gold nanorods (three samples with about 5 nm in diameter and 15.5, 19.1, and 24.6 nm in length) in real time with a time resolution around 50 ns. Plasmonic coupling enhances the signal of the diffusing gold nanorods, which are 1 order of magnitude smaller in volume (about 300 nm 3 ) than those used in our previous rotational diffusion experiments. We find a better angular sensitivity with plasmonic coupling in comparison to the free diffusion in the confocal volume. Yet, the angle sensitivity we find with plasmonic coupling is reduced compared to the sensitivity expected from simulations at fixed positions due to the simultaneous translational and rotational diffusion of the small nanorods. To get a reliable plasmonic sensor with the full angular sensitivity, it will be necessary to construct a plasmonic assembly with positions and orientations nearly fixed around the optimum geometry.

Authors 4

1. Nasrin Asgari Aachen Huygens-Kamerlingh Onnes Laboratory

   Leiden University

   Affiliation as printed

   Huygens-Kamerlingh Onnes Laboratory, Leiden University, Postbus 9504, 2300 RA Leiden, The Netherlands

2. Martin Dieter Baaske Aachen Huygens-Kamerlingh Onnes Laboratory

   Leiden University · Max Planck Institute of Biophysics

   Affiliation as printed

   Huygens-Kamerlingh Onnes Laboratory, Leiden University, Postbus 9504, 2300 RA Leiden, The Netherlands

   Max Planck Institute of Biophysics, Max-von-Laue-Str. 3, 60438 Frankfurt am Main, Germany

3. Jacco Ton Aachen Huygens-Kamerlingh Onnes Laboratory

   Leiden University

   Affiliation as printed

   Huygens-Kamerlingh Onnes Laboratory, Leiden University, Postbus 9504, 2300 RA Leiden, The Netherlands

4. Michel Orrit corresponding Aachen Huygens-Kamerlingh Onnes Laboratory

   Leiden University

   Affiliation as printed

   Huygens-Kamerlingh Onnes Laboratory, Leiden University, Postbus 9504, 2300 RA Leiden, The Netherlands