WARP: The Wave Riding Particles instrument - Characterization of liquid-solid-interfaces by simultaneous AI-based near real-time tracking and analysis of magnetic microparticle swarms as probes

• Applicants: Professor Dr. Arno Ehresmann; Dr. Rico Huhnstock; Professor Dr. Bernhard Sick
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 566304473

Probing the surface properties of a sample in a liquid environment is of interest in a vast range of disciplines, stretching from material science to the design of new nanostructures. For biological in vitro investigations, in particular, living organisms need to be studied in their natural, aqueous habitat. The same holds for proteins, bacteria, and viruses whose functions are closely connected to their shapes, which depend on the medium they are immersed in. Due to this high demand, several techniques have been established to analyze surface characteristics in liquids, among which atomic force microscopy (AFM) is arguably the most prominent. While providing high resolution, performing measurements where both sample surface and probing tip are surrounded by a liquid comes with its own peculiarities. For instance, contact with a liquid leads to undesired damping of the oscillating tip in dynamic measurement modes. Additionally, measurement times are limited by the scanning speed of the tip. In this project, we want to go beyond common probing techniques for surface properties in liquids and develop an experimental apparatus including an evaluation method based on artificial intelligence techniques that unravels liquid-mediated surface potentials. We intend to use magnetic microparticles as probes for the surface potentials, similar to an AFM tip, however, without attaching them to a cantilever. This approach bears the potential of massive parallelization as many particles can be tracked at the same time. The method relies on a combination of a dedicated hardware microscope setup with an automated three-dimensional particle tracking strategy. Movement of the particles close to and across the surface of interest will be realized by capturing them in a periodic magnetic stray field landscape generated by a magnetically patterned substrate sitting below the analyzed sample and superposing these static stray fields with external magnetic field pulses. We aim to develop a cantilever-free probing technique for liquid-mediated surface-surface interactions that surpasses the common AFM approach in 1.) measuring speed (many particles/probes allow for massive parallelization), 2.) measured area (AFM typically scans over a small range of a few microns), 3.) reliability (no artifacts from liquid-induced damping of vibrating elements) 4.) flexibility (variety of particle shapes and chemical surface groups possible), and 5.) simplicity (no deconvolution of sample and tip contributions necessary).

• DFG Programme: New Instrumentation for Research
• Major Instrumentation: Hochauflösende High-Speed Kamera