Sharmine Alam

Interaction and diffusion of gold nanoparticles in bovine serum albumin solutions

We studied the interactions of small sized, radius of 2.5–10 nm, gold nanoparticles (AuNPs) with bovine serum albumin (BSA). Fluctuation correlation spectroscopy (FCS) was used to monitor the changes in the Brownian diffusion of these NPs. Our results indicate a BSA monolayer formation at the NP surface with a thickness of 3.8 nm. The thickness of the adsorbed layer was independent of NP size. Best fit was obtained by the anticooperative binding model with the Hill coefficient of n = 0.63. Dissociation constant (KD) increases with particle size indicating stronger interaction of BSA with smaller sized NPs.

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

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.