Regensburg 2019 – scientific programme

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BP: Fachverband Biologische Physik

BP 12: Poster II

BP 12.17: Poster

Tuesday, April 2, 2019, 14:00–16:00, Poster B2

Surface relief scanning beyond the diffraction limit with optically trapped probes — •Matthias Allkemper, Lars Friedrich, and Alexander Rohrbach — Laboratory for Bio- and Nano-Photonics, Department of Microsystems Engineering - IMTEK, University of Freiburg, Germany

Optical traps play an increasing role in the bio-nano-sciences due to their ability to flexibly apply forces on tiny structures in fluid environments. Combined with particle tracking techniques they allow sensing miniscule forces exerted on these structures. Similar to atomic force microscopy (AFM), but much more sensitive, an optically trapped probe can be scanned across a structured surface to measure the height profile from the displacements of the probe. Here we demonstrate that by a combination of a time-shared twin-optical trap and nanometer-precise three-dimensional interferometric particle tracking reliable height-profiling and surface imaging is possible with a spatial resolution below the diffraction limit. The technique exploits the high energy thermal position fluctuations of the trapped probe, leading to a sampling of the surface 5000 times softer than in AFM. The measured height and force profiles from test structures and helicobacter cells illustrate the potential to uncover specific properties of hard and soft surfaces. We present a novel approach to minimize sticking events between surface and probe, by driving the trapped sphere in tapping mode.