Travelling wave tracking of microtubules

Travelling wave tracking is a technique that attains subnanometer spatial resolution (~0.3nm RMS) and ~10 microsecond temporal resolution. This allows us to scrutinize processes not only at biological relevant length scales but also at temporal scales required to observe their real time dynamics. Beyond these impressive specs, this new technique is unique in the sense that it does not apply external forces on the systems under study, thus detecting the natural dynamics with minimum external perturbations. Currently, the experimental set-up is rendering its first results.

The principle of this novel optical technique is based on tracking the movement of a single metallic nanoparticle (~80nm), which scatters light from a rapidly shifting interference pattern under total internal reflection. The phase and intensity of the scattered light depend sensitively on the position of the bead within the pattern and their simultaneous measurement allows the determination of the bead’s sub-nanometer displacement. While phase shifts provide information on displacements in the xdirection of the measurement plane (see figure), the intensity provides information of displacements in the z direction, though with less accuracy. Due to its fast response and high precision, the experimental configuration is particularly suited for studying movements of motor proteins along biological filaments.