Figure 7.

Experiments on initially living cells and comparison of preparation protocols. (a) Dark-field maps of three consecutive scans on an initially living D. discoideum cell in a microfluidic chamber. The scale bars denote 5 μm and the color axis is adjusted equally. The first and second scans are done with short exposure times and a reduced primary intensity of I₀ = 0.23 × I₀. All three dark-fields show slightly different intensity values, which becomes clearer in (b) background-corrected scattering signal I_cell(q_r) from the cell in panel a. The second measurement (orange curve) mainly coincides with the first scan’s data (in black), but intensity and the fitted exponent decrease significantly toward the long third scan (blue). (c) To compare the influence of preparation methods and measurements on the results, this scheme was applied to many measured cells, namely samples with initially alive cells, with formaldehyde-fixed cells, with cells that were frozen-hydrated (plunge-frozen), and with cells that were plunge-frozen and additionally freeze-dried. (Solid symbols) Scans on cells that have not encountered the dose of a fine scan (like shown in panel a, unless open symbols are used). (Small lines) Average value for one set of points; (solid lines) for solid symbols; and (dashed lines) open symbols. To see this figure in color, go online.