Frank Sommerhage

Transmission electron microscopy study of the cell–sensor interface

An emerging number of micro- and nanoelectronics-based biosensors have been developed for non-invasive recordings of physiological cellular activity. The interface between the biological system and the electronic devices strongly influences the signal transfer between these systems. Little is known about the nanoscopic structure of the cell–sensor interface that is essential for a detailed interpretation of the recordings. Therefore, we analysed the interface between the sensor surface and attached cells using transmission electron microscopy (TEM). The maximum possible resolution of our TEM study, however, was restricted by the quality of the interface preparation. Therefore, we complemented our studies with imaging ellipsometry. We cultured HEK293 cells on substrates, which had been precoated with different types of proteins. We found that contact geometry between attached cell membrane and substrate was dependent on the type of protein coating used. In the presence of polylysine, the average distance of the membrane–substrate interface was in the range of 35–40 nm. However, the cell membrane was highly protruded in the presence of other proteins like fibronectin, laminin or concanavalin-A. The presented method allows the nanoscopic characterization of the cell–sensor interface.

Membrane allocation profiling: a method to characterize three-dimensional cell shape and attachment based on surface reconstruction.

Three-dimensional surface reconstructions from high resolution image stacks of biological specimens, observed by confocal microscopy, have changed the perspective of morphological understanding. In the field of cell-cell or cell-substrate interfaces, combining these two techniques leads to new insights yet also creates a tremendous amount of data. In this article, we present a technique to reduce large, multidimensional data sets from confocal microscopy into one single curve: a membrane allocation profile. Reconstructed cells are represented in a three-dimensional surface from image sections of individual cells. We virtually cut segments of the reconstructed cell membrane parallel to the substrate and calculate the surface areas of each segment. The obtained membrane allocation profiles lead to morphological insights and yield an in vivo ratio of attached and free membrane areas without cell fixation. As an example, glass substrates were modified with different proteins (fibronectin, laminin, concavalin A, extracellular matrix gel, and both isomers of poly-lysine) and presented to HEK293 cells to examine differences in cell morphology and adhesion. We proved that proteins on a substrate could increase the attached portion of a cell membrane, facing the modified substrate, from an average of 32% (glass) to 45% (poly-lysine) of the total membrane surface area.

To establish a pharmacological experimental platform for the study of cardiac hypoxia using the microelectrode array

INTRODUCTION Simultaneous recording of electrical potentials from multiple cells may be useful for physiological and pharmacological research. The present study aimed to establish an in vitro cardiac hypoxia experimental platform on the microelectrode array (MEA). METHODS Embryonic rat cardiac myocytes were cultured on the MEAs. Following >or=90 min of hypoxia, changes in lactate production (mM), pH, beat frequency (beats per min, bpm), extracellular action potential (exAP) amplitude, and propagation velocity between the normoxic and hypoxic cells were compared. RESULTS Under hypoxia, the beat frequency of cells increased and peaked at around 42.5 min (08.1+/-3.2 bpm). The exAP amplitude reduced as soon as the cells were exposed to the hypoxic medium, and this reduction increased significantly after approximately 20 min of hypoxia. The propagation velocity of the hypoxic cells was significantly lower than that of the control throughout the entire 90+ min of hypoxia. The rate of depolarisation and Na(+) signal gradually reduced over time, and these changes had a direct effect on the exAP duration. DISCUSSION The extracellular electrophysiological measurements allow a partial reconstruction of the signal shape and time course of the underlying hypoxia-associated physiological changes. The present study showed that the cardiac myocyte-integrated MEA may be used as an experimental platform for the pharmacological studies of cardiovascular diseases in the future.

Bioelectronic Detection Schemes for Biomedical and Environmental Sensing

An artificial nose or tongue could be a real benefit at times: this kind of biosensor could sniff or taste out poisons, explosives or drugs, for instance. The senses of living organisms function using various mechanisms, among other things utilizing membrane proteins as receptors. Membrane proteins have several important functions in the cell, one of which is to act as receptors, passing on signals from molecules in the air or liquid, for example, to the cell interior. This article is focusing on the functional coupling of biological signal processing and recognition elements with micro- and nanoelectronic semiconductor devices and circuits for the development of future biosensors and molecular diagnostics tools.