3D Carbonate Calcium polymorphs imaging with Stimulated Raman scattering in Biominerals

Abstract

We present a highly sensitive coherent Raman microscopy approach, which allows for the tridimensional (3D) imaging of series of carbonate polymorphs in marine organisms. CaCO3 biomineralization occurs from the transformation of metastable amorphous precussors and other crystalline phases into a final crystalline phase. Undertanding biomineralization pathways requires identifying this physico-chemical temporal sequence. Our approach exploits the different vibrational signatures of amorphous calcium carbonate, aragonite, calcite, Mg-Calcite or hemi-hydrated calcium carbonate. This optical method enables the production of spatially and spectrally resolved images of the different compounds. When applied on the growing edge of post mortem sample of both Pinctada margaritifera pearl oyster shell and Stylophora pistillata coral, it allows for infering a temporal crystalisation sequence. We thus highlight the existence of intermediate crystalline phases, involving magnesian calcite or hemi-hydrated calcium carbonate, respectively.