Regensburg 2019 – scientific programme

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BP: Fachverband Biologische Physik

BP 8: Cytoskeletal filaments

BP 8.6: Talk

Tuesday, April 2, 2019, 10:45–11:00, H10

Germanium nanospheres as high precision optical tweezers probes — •Swathi Sudhakar and Erik Schaeffer — Cellular Nanoscience, Center for Plant Molecular Biology, Eberhard Karls University of Tuebingen, Tuebingen, Germany.

Force spectroscopy on single biological molecular machines is often performed using optical tweezers. Commonly microspheres composed of silica or polystyrene are trapped in a highly focused laser beam and are used as handles to measure the mechanics of motor proteins such as kinesin. The ultimate precision of such experiments is limited by thermal fluctuations and, among others, the size of the microsphere. Thus, ideally, microspheres should be as small as possible. However, since trapping forces scale with the particle volume, maximum trapping forces quickly approach motor-generated forces creating a lower practical size limit of about 200 nm for polystyrene microspheres when studying kinesin motors. Here, we have developed germanium nanospheres with diameters ranging from 30-200 nm. With a high refractive index of 4.4, their trapping efficiency and maximum force per power is more than 10-fold improved compared to equal-sized silica spheres. Using 70-nm-diameter germanium nanospheres, we measured the stepping behavior of kinesin-1. With an improved precision, we could measure intermediate steps of kinesin. In the long-term, the development and application of novel high-precision probes will provide new insight into the working mechanism of molecular machines.