Figure 5: Diffusion limitation by ice microstructure.
(a) Principle of the in-ice diffusion assay. Ice microstructure limits the exposure of primer-coated 1 μm-diameter beads to diffusing ribozyme; hence, only a subset of the beads experience primer extension (red). (b) Fluorescence-activated cell sorting profiles of beads from different MgCl2 ices (after 8 days diffusion). Beads with many extended primers (red) gain fluorescence during processing. (c) The extent of ribozyme diffusion after 8 days (as measured by the percentage of fluorescent beads) through ices with different solute levels and magnesium counterions (filled diamonds, MgCl2; open squares, MgSO4; means ± s.e.m.; n=3). (d) The structure of the eutectic phase in diluted MgCl2 reactions, imaged by freeze-fracture SEM. The lighter, raised web of channels represents the eutectic phase.
