Figure 4. X-ray fluorescence microscopy and tomography provides zinc quantification and mapping within the egg.

(a) Bionanoprobe XFM images of a 400 nm thick egg section. Zn, Cu, and Fe maps shown with concentration ranges. Scale bar = 10 µm, pixels = 100 × 100 nm². High [Zn] observed in punctate cortical structures.

(b) Histogram of [Zn] in punctate regions (bins = 0.05 M). Data fitted to a Lorentzian distribution (black line) centered on [Zn] = 0.2 M.

(c) XFM tomography images at 0° angle of intact MII egg following zinc fixation. Zn (i), S (ii), Cu (iv), Fe (v), and Ca (vi) maps shown with concentration ranges. Zn/S map overlay (iii) demonstrates zinc-rich regions are intracellular. Scale bar = 20 µm.

(d) Total metal content quantification in resin-embedded MII egg following zinc fixation. Bars represent average number of atoms over 60 projection images of the same sample (Fe = 8±4 × 10⁹; Cu = 5±3 × 10⁹; Zn = 6±2 × 10¹⁰). Error bars represent ± S.E.M. Dashed lines represent previously measured values in unfixed eggs.⁵ Results indicate that this zinc fixation protocol preserves total Zn content.

(e) Zn maps at several angles (° indicated) illustrate a cortical, hemispherical distribution of Zn-enriched regions.