PNNL

Abstract

Understanding biomineralization relies on imaging chemically heterogeneous organic-inorganic interfaces across a hierarchy of spatial scales. Further, organic minority phases are often responsible for emergent inorganic structures, from the atomic arrangement of different polymorphs, to nano- and micrometer crystal dimensions, up to meter size mollusk shells. The desired simultaneous chemical and elemental imaging to identify sparse organic moieties, across a large fields-of-view, and with nanometer spatial resolution, has not yet been achieved. Here, we combine nanoscale secondary ion mass spectroscopy (NanoSIMS) with spectroscopic nano-IR imaging for simultaneous chemical, molecular, and elemental nanoimaging. At the example of Pinctada margaritifera mollusk shells we identify and resolve ~50 nm interlamellar protein sheets periodically arranged in regular ~600 nm intervals. The striations typically appear ~15 µm from the nacre-prism boundary at the transition between disordered neonacre to mature nacre. Using the polymorph distinctive IR-vibrational carbonate resonance, the nacre and prismatic regions are consistently identified as aragonite (? ¯_a=860 cm-1) and calcite (? ¯_c=880 cm-1), respectively. While the morphology of the nacre tablets varies across the nacre, the polymorph identities are spatially uniform to within 10’s of nanometers between their interfaces. These results show with the identification of the intertablet protein layer how correlative nano-IR chemical and NanoSIMS elemental imaging can help distinguish different models proposed for shell growth in particular, and how organic function may relate to inorganic structure in other biomineralized systems in general.