Correlating Surface Plasmon Resonance Microscopy of Living and Fixated Cells with Electron Microscopy Allows for Investigation of Potential Preparation Artifacts

The investigation of the cell–substrate interface is of great importance for a broad spectrum of areas such as biomedical engineering, brain‐chip interfacing, and fundamental research. Due to its unique resolution and the prevalence of instruments, electron microscopy (EM) is used as one of the standard techniques for the analysis of the cell–substrate interface. However, possible artifacts that might be introduced by the required sample preparation have been the subject of speculation for decades. Due to recent advances in surface plasmon resonance microscopy (SPRM), the technique now offers a label‐free alternative for the interface characterization with nanometer resolution in axial direction. In contrast to EM, SPRM studies do not require fixation and can therefore be performed on living cells. Here, a workflow that allows for the quantification of the impact of chemical fixation on the cell–substrate interface is presented. These measurements confirm that chemical fixation preserves the average cell–substrate distances in the majority of studied cells. Furthermore, it is possible to correlate the SPRM measurements with EM images of the cell–substrate interface of the exact same cells, thus identifying regions of good agreement between the two methods and revealing artifacts introduced during further sample preparation

Superlattice growth and rearrangement during evaporation-induced nanoparticle self-assembly

Understanding the assembly of nanoparticles into superlattices with well-defined morphology and structure is technologically important but challenging as it requires novel combinations of in-situ methods with suitable spatial and temporal resolution. In this study, we have followed evaporation-induced assembly during drop casting of superparamagnetic, oleate-capped gamma-Fe2O3 nanospheres dispersed in toluene in real time with Grazing Incidence Small Angle X-ray Scattering (GISAXS) in combination with droplet height measurements and direct observation of the dispersion. The scattering data was evaluated with a novel method that yielded time-dependent information of the relative ratio of ordered (coherent) and disordered particles (incoherent scattering intensities), superlattice tilt angles, lattice constants, and lattice constant distributions. We find that the onset of superlattice growth in the drying drop is associated with the movement of a drying front across the surface of the droplet. We couple the rapid formation of large, highly ordered superlattices to the capillary-induced fluid flow. Further evaporation of interstitital solvent results in a slow contraction of the superlattice. The distribution of lattice parameters and tilt angles was significantly larger for superlattices prepared by fast evaporation compared to slow evaporation of the solvent