Observation of time-dependent single-particle light scattering from gold nanorods and nanospheres by using unpolarized dark-field microscopy

We report on the time-dependent light scattering from single gold nanospheres (diameter about 90 nm) and nanorods (15x25 nm). Unlike the recent report by S&diaero;nnichsen and Alivisatos (Nano Lett. 5, 301-304, 2005), we observed the dynamic modulation of scattering intensity by using unpolarized dark field microscopy equipped with a digital camera. The changes in light scattering intensity from gold nanorods were caused by 3-dimensional rotational diffusion by contrast to 2-dimensional polarized-scattering modulation observed previously. In the case of 90-nm gold nanospheres, the light scattering modulation was related to the translational diffusion only. By using T-matrix method and Rayleigh approximation, we describe the time-dependent variations in light scattering intensity caused by rotation of nanorods at several scattering and orientation geometry. Finally, we present preliminary data on real-time visualization of active interaction between the living rat peritoneal macrophages and gold nanorods.

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