Three dimensional tracking of gold nanoparticles using digital holographic microscopy

The tracking of nano-scale biological markers in motion is a challenging project, that could lead to a better understanding of dynamics in biological systems. Since digital holography gives access to the whole light field in a volume from a single hologram [1, 2], this technique is suitable to reconstruct the field scattered by gold particles in three dimensions, and then determine their positions. This localization can be done without any mecanical scanning of the setup. The 3D tracking in digital holography was demonstated for micron-size particles in several publications with in-line holography [3–6]. The observation of nano-scale gold particles was also demonstrated in off-axis holography by Atlan et al. [7], and on the membrane of a living cell by Joud et al. [8]. Nano particles could be observed with the combination of off-axis geometry and phase-shifting technique [9], that achieves almost the theoretical noise level [10]. In this paper, we present first our digital holographic microscope, then we explain the reconstruction method. Some results of 3D tracking of 100 nm nano-beads are presented.