Investigation of biological model systems by Atom Probe Tomography

• Applicant: Professor Dr. Guido Schmitz, since 10/2024
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry ; Biomaterials ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 509488204

Atom probe tomography (APT) allows the investigation of structures on the nanoscale and is based on the controlled field evaporation of single atoms and enables computer-aided reconstructions of the evaporated volume with atomic resolution. In order to achieve the very high field strengths required for field evaporation, the samples must be in a special, needle-shaped geometry, with a radius of curvature of about 50 nm. In recent years, this analytical measurement method has opened up a wide range of applications, due to continuous further development of microscopes and sample preparation techniques. Due to its particularly high chemical sensitivity, APT, in combination with electron microscopy, can help to study and understand processes at internal interfaces. One class of materials that has hardly been explored to date is the class of biological materials or "soft matter". Since biological processes can often only occur in aqueous environments, appropriate sample preparation is required to bring these samples into the geometry necessary for APT. For liquid samples in particular, a closed cryopreparation chain is required. The procedures must be adapted to avoid crystallization of the liquid during cooling. The original structure would otherwise be destroyed by the volume expansion of the ice crystals. It can be assumed that the mechanical stability of frozen samples is significantly lower than that of solids, especially metals. Thus, a drop in the success rate of successfully measured samples can be expected. This is further complicated by the fact that the evaporation of organic compounds is not atomic, but molecular. The recorded mass spectra are much more complex and leave room for interpretation. There may also be variations in chemical composition, as light gases such as oxygen and nitrogen exhibit loss mechanisms. The dependence of the measured signals is much more influenced by the experimental conditions such as laser power, field strength, wavelength, temperature. The expected artifacts due to the possibly inhomogeneous evaporation of the samples have not yet been considered in any reconstruction algorithm. It is unclear whether a suitable reconstruction of the volume is possible. This is where this project would like to start and try to determine, among other things, the local geometric and chemical resolving power using suitable calibration samples. The aim of this project is to explore the possibilities and current limitations of APT in the analysis of biological systems, using known biological model systems as examples, and to find ways and solutions to overcome the obstacles identified.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Dr. Patrick Stender, until 9/2024