Photothermal Imaging and Tracking of single Metallic Nanoparticles on Live Neurons

Modern optical methods allow the study of biological systems on the level of individual molecules in vivo; yet they all are limited either by the size of the marker, 40 nm and above in the case of single particle tracking (SPT) approaches, or by the short lifetime of fluorescent dyes, which typically bleach in seconds or less. The project presented in this proposal aims at solving both limitation by adapting photothermal intereference contrast imaging for use on live cells. This new method uses a system similar to classic differential intereference contrast (DIC) to detect the slight change in refractive index caused by the locally confined heating of a small gold bead. In doing so, it provides a non-saturating, non-bleaching, and biologically inert, yet specifically and covalently attachable marker, which is small enough to allow studies in restricted volumes such as the synaptic cleft of neurons. Preliminary in vitro experiments have shown that photothermal imaging of 2.5 nm metallic beads is feasible, even in a strongly scattering environment. The combined expertise in both the optical as well as biological aspects of this project, which is guaranteed by the close collaboration of the Nanophotonic and Cellular Physiology groups at the Université Bordeaux, provides the best conditions for the development of this new and powerful technique into a real-time tracking method which can be applied to live cells.