Motion of gold nanorods on the fluid lipid bilayer and cell plasma membranes: Interfacial Nanorheology*

We measure the thermal motion of single gold nanorods (GNR) at plasma membranes and on Giant Unilamellar Vesicles (GUV). The goal of this study is to develop a high throughput assay to utilize the 3-d orientation and trajectory of a GNR adhered to the cell plasma membrane to probe its mechanical state. It has been hypothesized that change in surface tension and curvature distribution of the cell membrane affects the liver cancer behavior such as proliferation and matrix production. We bind the GNR to the plasma membrane and model lipid bilayers by functionalizing its surface by magainin peptides. Laser-illuminated dark-field microscope and polarimetric analysis are developed to track the GNR’s 3-d orientation to a precision better than one degree. In plane angular and translational motion of the nanorods are measured to determine the interfacial viscoelasticity of the membrane by incorporating the hydrodynamic drag force on the GNR. Out of plane reorientation of the GNR are analyzed to study the membrane undulation dynamics and to deduce membrane modulus and the surface tension.