Viscosity imaging using heterodyne holographic spectral analysis of Brownian nanorods rotation

Under polarized illumination, non-spherical objects display anisotropic scattering, and their rotation induces a blinking. We present a method based on heterodyne holography to measure images of the Brownian rotation frequencies of gold nanorods over a broad frequency range (0-10 MHz). Since Brownian rotation often occurs on shorter space and time scales than translation, it can provide local viscosity measurements, and high resolution imaging is possible. Here, we demonstrate that viscosity contrast imaging is revealed by heterodyne imaging at one or several investigation frequencies. After calibration, a frequency scan can give access to quantitative viscosity imaging.