Innovative Electron Microscopy
Characterization of materials at the nanoscale is essential for the progress of modern nanotechnology, energy science, biology, and biomedical sciences. The Program Division Innovative Electron Microscopy conducts interdisciplinary research at the interface of physics of electron microscopy, cancer research, biophysics, materials science, and image processing. Our research focuses on, among other topics, deciphering the molecular mechanisms behind drug-resistance development in HER2-overexpressing cancer. This research has the potential to identify predictive markers for personalized medicine. We develop forefront in situ electron microscopy methods for the study of functional materials and biological samples at native conditions, with a focus on liquid-phase electron microscopy (LP-EM). We are also exploring new routes for three-dimensional (3D) data acquisition using dedicated software and Machine Learning. We have extensive experience with image processing and particle detection methods, as well as with developing protocols for the specific labeling of proteins with nanoparticles. We have established various research collaborations with both academia and industry.
Today, cancer is the leading cause of death in industrialized countries with HER2 overexpressing breast cancer being among the most common and dangerous cancers affecting women. We characterize the role of human epidermal growth factor receptor (EGFR) and EGFR 2 (HER2) in cancer cells. Of key interest is the analysis of differences in protein function between individual cancer cells (cancer cell heterogeneity) and between distinct functional membrane regions within the same cell. With our approach, it is possible to study the effect of cancer drugs on small sub-populations of cells, with the goal of deciphering the molecular mechanism behind drug-resistance development. The outcomes of our research have the potential to develop predictive markers that increase the effectiveness of drugs in a personalized approach.
Fig. 1: Correlative light microscopy and LP-EM of HER2 proteins in breast cancer cells . (A) Fluorescence image showing several dozens of cells. HER2 proteins were labeled with fluorescent QDs. (B) LP-EM image of a membrane region of a cancer cell showing the locations of HER2 receptors labeled with quantum dots. The overlay reflects a molecular model. From: Sci. Adv. 1:e1500165, 2015.
TAlthough membrane proteins are the targets of ~60% of today’s drugs, our knowledge about their functioning is often limited as a consequence of the lack of analytical methods. With LP-EM, we have already achieved nanometer resolution for labeled proteins in fixed cells, this is sufficient to resolve individual proteins and infer the functional state of protein complexes. Within the Collaborative Research Centre 1027 at Saarland University entitled “Physical modeling of non-equilibrium processes in biological systems”, we study the question of how the cell spatially organizes proteins of a certain functional state in a specific plasma membrane location. Here, we focus on the interplay of the proteins ORAI1, EGFR, and HER2, and actin filaments. More information.
Fig. 2: LPEM of a whole cell. (A) Scheme of a cell in a liquid layer covered by a graphene sheet on a thin SiN membrane imaged with a STEM electron beam. (B). Overview image of whole SKBR3 cancer cells in liquid. (C) Image of the boxed region in B showing individual HER2 proteins labeled with QDs at a spatial resolution of 3 nm. From: Biophys. J. 115, 503 (2018)
Fig. 3: AuNPs arranged in a rhombitrihexagonal pattern imaged with LP-EM in toluene. From: Sci. Adv. 6, eaba1404 (2020)
Electron microscopy of liquid specimens offers unique opportunities to study the nanometer-scale dynamic processes occurring at liquid interface. Our research resulted in new fundamental insights in nanoscale dynamics and local van der Waals interactions. We discovered that nanoparticles in close proximity to a surface do not move as predicated by Brownian motion, but rather many orders of magnitude more slowly. We study self-assembly processes of nanoparticle super lattices at the solid-liquid interface via in situ electron microscopy. More information.
In our group, we have developed a breakthrough LP-EM technology to image whole eukaryotic cells in their native liquid state. For LP-EM studies, proteins are specifically labeled with electron dense nanoparticles, for example, quantum dots. The atomic number (Z) contrast of scanning transmission electron microscopy (STEM) is then used to image the nanoparticles within a layer of liquid containing the cells. Our latest research involves graphene liquid enclosures. We also develop software for label detection, intelligent data acquisition strategies for 3D electron microscopy, and time-resolved LP-EM using Machine Learning. More information.
Fig. 4: Liquid STEM principle. From: Proc. Natl. Acad. Sci. 106, 2159-2164 (2009).
At the INM, we have established a state-of-the-art electron microscopy infrastructure including an aberration-corrected scanning transmission electron microscope (STEM, ARM200, JEOL, Japan), with a combined energy filter and an electron-energy-loss analyzer (Gatan) g. This microscope has a cold field emission source (CFEG) with low energy spread. The main operation of the microscope is for LP-EM, but it is also used for various other areas of research at the institute, Saarland University, and beyond.
Figure: Picture of the JEOL ARM200F.