Nanoparticle transport through macromolecular fluids plays important roles in several interdisciplinary fields of studies ranging from polymer science to drug delivery. But the diffusion of asymmetric nano-objects, such as rods, through polymer solutions is poorly understood in spite of their growing applications. Here by using a novel multiphoton fluctuation correlation spectroscopy (MP-FCS) technique, we investigated the translation and rotational diffusion of gold nanorods (AuNRs) in polyethylene glycol (PEG) solutions of varying volume fraction and molecular weights. We determined the nanoviscosity experienced by the NRs and compared it with the theoretical studies of nanosphere diffusion in semidilute and entangled polymer solutions. Our results showed the importance of nonhydrodynamic friction and the effects of polymer dynamics in determining the transport of the nanoparticles.

Study of interaction ofZnO nanoparticles with human serum albumin using fluorescence spectroscopy AIP Conf. Proc. 1512, 130 (2013); 10.1063/1.4790945 Studies on CdS nanoparticles prepared in DNA and bovine serum albumin based biotemplates

We used polarized fluctuation correlation spectroscopy (p-FCS) to study the interaction of bovine serum albumin (BSA) with cetyl­tri­methyl­ammonium bromide (CTAB) stabilized gold nanorods (AuNRs). The translational (D T) and rotational diffusion (D R) of the BSA-NR conjugate were determined in varying concentrations of BSA. The measured diffusion coefficients were analyzed to determine the change of the hydrodynamic size of the particle due to protein adsorption. We found that the saturation coverage is less than one monolayer of protein at a BSA concentration of ≈1 mM. The adsorption isotherm was compared with the Langmuir and anticooperative binding models to quantify BSA-NR association. Our data can be interpreted in terms of hydrophobic interaction between the imperfect CTAB coating and the buried hydrophobic residues of the protein, which results in the loss of protein native conformation. We compared our study with previous experiments involving carboxylic-acid-stabilized nanosphere interaction with BSA molecules, and significant differences were found.

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.