Thesis-PDF - IAP/TU Wien

Figure 6.1: A burst E. gracilis cell. The pellicle is torn apart and due
to the inner pressure of the cell the cytoplasm including cell organelles is
ejected. If the cell has not been fixated, enzymatic activity starts to dissolve
tissue, making AFM investigation even more difficult. Intermittent contact
mode AFM image, Amplitude trace.
successful imaging. The proper balance is required for the residue to support the
cell enough against bursting but not to cover it.
Much better results were achieved following the steps from section 5.3.2, Fig.
5.7 (on page 75) to avoid too much and too little embedding of the cells. In Fig.
6.3 the basal part of a well embedded E. gracilis cell is shown. The material
embedding the cell alters its surface roughness around 5 µm away from the cell.
Such samples proved to be exellent for AFM imaging, especially in intermittent
contact mode under ambient conditions and could well be used for for several days.
It was assumed that scanning under liquid, because of the absence of a water
meniscus between tip and sample (see section 3.2.1, page 27, could enhance image
resolution but was found to pose another range of difficulties. Algal cells do hardly
attach to even functionalized (e.g. poly-l-lysine or gelatin coated) glass supports,
and a stable positioning of the scanned surface was not reached. The imprint in
Fig. 6.4 was left by a E. gracilis cell that detached from a poly-l-lysine coated glass
slide in liquid. The negative forms of the algal pellicular strips in the substrate
surface can be well seen. A comparison of cell length usually measuring more than
40 − 80 µm and imprint length around 6 µm indicates a relatively small area of
contact. A stable imaging surface however is a prerequisite for reproducible high
resolution AFM imaging.
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