  The 3D structure of light scattering from dark-field illuminated live 3T3
cells marked with 40 nm gold nanomarkers is explored. For this purpose, we use
a high resolution holographic microscope combining the off-axis heterodyne
geometry and the phase-shifting acquisition of the digital holograms. Images
are obtained using a novel 3D reconstruction method providing longitudinally
undistorted 3D images. A comparative study of the 3D reconstructions of the
scattered fields allows us to locate the gold markers which yield, contrarily
to the cellular structures, well defined bright scattering patterns that are
not angularly titled and clearly located along the optical axis. This
characterization is an unambiguous signature of the presence of the gold
biological nanomarkers, and validates the capability of digital holographic
microscopy to discriminate them from background signals in live cells.
