Fig. 2: Cryo-STEM-EDS imaging reveals a high concentration of nitrogen in crystals and organelles.
From: pH variations enable guanine crystal formation within iridosomes
a, Cryo-STEM dark-field image of guanine crystals and organelles from the edge of an isolated iridophore of a 72 hpf larva. In total, 23 cells isolated from dozens of larvae were imaged and analyzed. Right, cryo-STEM-EDS maps of nitrogen (green), carbon (red) and oxygen (purple). b, ED patterns from the corresponding locations (1–3) in the dark-field image, including intracellular organelles (1, pink; 3, orange) and a crystal (2, blue). c, EDS spectra corresponding to the marked ROIs in a: intracellular organelles (pink and orange frames) and a crystal (blue frame). Inset, closer view of the 0.2–0.6 keV region. d, Graph illustrating the N/C ratio, comparing organelles (n = 61 from 23 cells, orange) and crystals (n = 22 from 6 cells, blue; two-sided F-test, F60,21 = 3.4517, P = 0.002618). The mean values ± s.d. are shown on the graph.
