Analyzing Polymer-Grafted Gold Nanorods using Depolarized Dynamic Light Scattering (DDLS)

Polymer-grafted gold nanoparticles (AuNPs) are a class of materials that combine the structural and optical properties of colloidal AuNPs with the stability of a polymer canopy. This unique combination allows for an array of potential biomedical applications such as drug delivery and catalysis. Unlike spherical grafted AuNPs, which are well-studied, grafted anisotropic AuNPs are not fully understood. Our goal is to study the effects of grafting thiolated Polyethylene Glycol (PEG) polymer to gold nanorods (AuNRs) on diffusive properties of the grafted AuNRs. The Depolarized Dynamic Light Scattering (DDLS) on two different setups was used to deduce the size of both bare and grafted AuNRs from their measured translational and rotational diffusion. This approach requires a multiangle DDLS experiment with critical analysis of the measured VV and VH correlation functions to yield the measured VV and VH decay rates of each system. The basic scattering theory for shorter (qL<3) cylinders allows to deduce nanorod translational and rotational diffusion coefficients from the measured angular dependencies of the decay rates. To obtain the apparent dimensions of the particles de La Torre's straight cylinder (SC) model was used. It was found that the polymer grafted nanorods were as expected larger in diameter and largely unchanged in length. While two DDLS systems in general produced consistent results an unexpected difference in measured correlation functions was encountered. In particular, one DDLS setup produced an additional mode of the VV correlation function, the origin of which we are trying to understand.