Investigation of Cell-Sensor Hybrid Structures by Focused Ion Beam (FIB) Technology
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0983-LL03-03
Investigation of Cell-Sensor Hybrid Structures by Focused Ion Beam (FIB) Technology Andreas Heilmann1, Frank Altmann1, Andreas Cismak1, Werner Baumann2, and Mirko Lehmann3 1 Fraunhofer Institute for Mechanics of Materials, Halle (Saale), 06120, Germany 2 Biophysics Department, University of Rostock, Rostock, 18057, Germany 3 Micronas GmbH, Freiburg, 79108, Germany ABSTRACT For the investigation of the adhesion of mammalian cells on a semiconductor biosensor structure, nerve cells on silicon neurochips were prepared for scanning electron microscopy investigations (SEM) and cross-sectional preparation by focused ion beam technology (FIB). The cross-sectional pattern demonstrates the focal contacts of the nerve cells on the chip. Finally, SEM micrographs were taken parallel to the FIB ablation to investigate the cross section of the cells slice by slice in order to demonstrate the spatial distribution of focal contact positions for a possible three-dimensional reconstruction of the cell-silicon interface. INTRODUCTION Cell adhesion is a very important biological process with fascinating research challenges. In general, cell adhesion leads to the formation of an apical membrane at the non-contacting cell surface and a basolateral membrane along the contacting cell surface [1-3]. Examples range from the formation of specific organs to the assembly of blood vessels. Furthermore, the adhesion plays an important role in the selection of biomaterials or for a better understanding of the interaction between the cell and the substrate, which is responsible of the sensor signal. For choosing a material for implantation into the body, for in vitro technologies or for a sensor for the analysis of cells, substantial knowledge about the way how the cells adhere to the materials is necessary. There is a lot of data available as far as molecular aspects of the adhesion process are concerned. Nevertheless much remains unclear. Therefore, in addition to molecular research more biophysical aspects are being investigated [4,5]. Furthermore, there are optical methods which give data about the adhesion of a cell on a solid surface. These optical methods, like Interference Reflection Microscopy depend on optical phenomena at interfaces [6]. In general, there is no method for a directly visualising the interspace. In this paper, we present a new method to visualize the cell-substrace interspace directly. It is based on the focused ion beam (FIB) Technology, which is an established method in semiconductor R&D and quality departments for the analysis of electronic devices. For this purpose, samples from ion-sensitive field emission transistors (ISFET) with cell cultures [7-8] have been prepared as usual for scanning electron microscope (SEM) investigations of biological samples [9]: Primary fixation in glutardialdehyde, postfixation with osmium tetroxide, dehydration and drying with critical point Technology. Finally, the samples were coated with a thin platinum layer to prevent surface charging. During this extensive sample prep
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