Translational Anisotropy and Rotational Diffusion of Gold Nanorods in Colloidal Sphere Solutions

Abstract

We studied the translational and rotational diffusion of gold nanorods within a rod/sphere composite liquid using fluctuation correlation spectroscopy (FCS). The nanorods of length L ∼ 60 nm and diameter d ∼ 17 nm were used at a fixed concentration of ∼1 pM. The concentration of colloidal Ludox spheres (size ∼ 26 nm) was varied up to a volume fraction of ϕ = 0.3 or approximately 7 spheres/L(3). Our experiments showed significant translational anisotropy as the sphere concentration was increased. The translational diffusion parallel to the rod axis (D(T∥)) followed very close to the bulk viscosity of the solution. However, the diffusion normal to the rod axis (D(T⊥)) experienced a significantly higher frictional force. For volume fraction ϕ > 0.1 a slightly modified caging theory by Pecora and Deutch could explain the rotational diffusion of the rods very well. At low volume fraction the agreement is poor, which we interpreted as modification of the local ordering of the spheres, which can affect the rod rotation.

Nanoscale Rheology and Anisotropic Diffusion Using Single Gold Nanorod Probes

“…While the use of anisotropic nanoparticle tracers would greatly facilitate the application of this approach to stiffer materials and much smaller length and time scales than possible with larger tracers, microrheology places stringent requirements on the accuracy of the tracer's inferred meansquared displacement. Indeed, despite several reports of gold nanorod (GNR) rotational tracking using imaging [19][20][21][22][23][24][25][26][27][28][29][30][31] and depolarized scattering [32][33][34][35][36], no one has demonstrated the use of GNRs to accurately measure the rheology of a viscoelastic material. Moreover, no models of the complex anisotropic translational diffusion [32,33,37] that these particles would execute in a viscoelastic material, or its coupling to the rotational diffusion, have been reported or validated.…”

Polarization-dependent fluorescence correlation spectroscopy for studying structural properties of proteins in living cell

“…However, owing to several technical limitations, the rotational diffusion of proteins has not been measured using FCS. Previous reports showed that by using pol-FCS, rotational diffusion can be clearly observed in the case of peptide-coated nanorods 6 , Qrod 7 , gold nanorods 8 9 10 , quantum dots 6 , DNA-DAPI 11 , and large polymers 12 . Further, a positive relationship between translational and rotational diffusion was observed in the viscosity change of a solvent 13 .…”

Size effects on rotational particle diffusion in complex fluids as probed by Magnetic Particle Nanorheology

“…the scaling behavior of Z app vs. f is expected to be weaker for rotation than for translation, and might further be affected by a depletion layer. 38,43,45,46 Even if the latter was not the focus of the present study, we hope that our results foster the development of a more developed theoretical framework for rotational diffusion in complex fluids and might give rise to upcoming detailed theoretical description focusing on rotation. In view of the versatility and broad applicability of the method, along with the actual development of similar or related approaches, this would be very attractive.…”

“…Based on the experimental and theoretical considerations of others, 27,38,[43][44][45] e.g. the scaling behavior of Z app vs. f is expected to be weaker for rotation than for translation, and might further be affected by a depletion layer.…”