Polarization- and wavelength-dependent defocused scattering imaging of single gold nanostars with multiple long branches.

The scattering properties of gold nanostars (AuNSs) are not completely understood. Furthermore, there have been no studies on the dark-field (DF) scattering patterns of a AuNS in defocused DF microscopy. Herein, we demonstrate the polarization- and wavelength-dependent defocused scattering properties at the localized surface plasmon resonance (LSPR) wavelengths of single AuNSs with multiple long branches protruding from their surfaces. The defocused scattering intensities of single AuNSs at two LSPR excitation wavelengths changed periodically as a function of the rotational angle of a polarizer, whereas the doughnut-shaped scattering pattern remained unaltered. Furthermore, the characteristic doughnut-shaped defocused scattering pattern enabled the resolution of the spatial field distributions of single dipoles on the same AuNS surface at two LSPR wavelengths. Finally, we tracked the real-time rotational dynamics of a AuNS rotating on a glass slide using defocused microscopy. These results provide a deeper understanding of the defocused scattering properties of single AuNSs with multiple sharp, long branches randomly protruding from their surfaces.