SFM Observations of Living Cells
The observation of human living cells by scanning force microscopy (SFM) has obtained increased interest since SFM has become a standard tool in surface analysis. SFM has been successfully used to image biological samples in air or in liquid. In contact mode SFM, briefly described, a tip at the end of a cantilever touches the surface with a constant force and scans line by line the sample. Unfortunately, the resolution of the image is mainly limited by the softness of the sample and the interaction with the scanning tip.
Cells of the cell lines UMSCC7, UMSCC11, UMSCC22b, Chondrozytes and SFC are used. The UMSCC7 is a lung tumor cell line, SFC is of phagocytes type and the others are head-neck tumor cell lines. The cells are cultured 3 days before observation as described elsewhere . Than the samples are portioned, one probe kept as reference (non treated), one probe applied with the antitumor drug HpD. Most of the drug treated cells died (around 2-5 % survivor). The residues were separated by centrifugal process and also investigated by SFM.
SFM measurements were done in constant force contact mode at room temperature (Nanoscope III, Digital Instruments). Cells adhered on a special culture glass were observed in air and in solution. When the tip approaches on the surface normally the value of -2 V increased to 0 V, indicative to surface contact. This is always observable in air after a period of 1 hour, when most of the cells are dried up.
It is of much more complex handing, when the tip approaches to the surface of living cells. Nearby 0 V (around -0.1 V) the value skip to -2 V. An explanation may be, that the cell dodges the tip. Repeating the procedure gives reproduced values. Likewise, when the surface approaching is successful the living cell induces electronic signals disturbing the scan. It seems, that the cells are tickled by the tip (or the applied potential) and shake themselves. All these troubles are finished when the cells died. Nice topographic insights were received. In this study we also investigated the tumor cells (UMSCC-type) after treatment with HpD. HpD is known as enhancing irradiation effects in cancer cells by reducing the energy supply, leading to an irreversible inhibition of DNA repair, increased cytogenetic damage and cell death. In the present study, this could partly be visualized by observing tumor cells incubated with HpD, and investigated by light microscopy and SFM techniques. There a distortion of the cell and its membrane under drug influence is visible, with the exception of the lung tumor cells. They much more resistant to oxidation processes survive to a great extent. In the shattered tissues three dimensional chiral associations induced by the drug were observed (spirals and helices).
 Lindl, T.; Bauer, J. "Zell- und Gewebekultur", Gustav Fischer Verlag, Stuttgart-Jena-New York, 1994
G. Bischoff1, D. Riemann3 R. Bischoff2,, J. Langner3 S. Hoffmann1
1 Martin Luther University Halle-Wittenberg, Institute of Biochemistry,