Abstract
Occlusion of organic components in synthetic calcite crystals has been recently used as a model to understand the role of intra-crystalline organics in biominerals. However, the characterization of the distribution of both types of organics inside these calcite crystals is very challenging. Here, we discuss the potential of using the technique of atom probe tomography (APT) for such characterization, focusing on the analysis of chitin incorporation in single crystals. Additionally, APT has at least the same spatial resolution as TEM tomography, yet with the advantage of obtaining quantitative chemical data. Results show that chitin, either after degradation with yatalase or in the form of nanofibers, forms discrete clusters (2 to 5 nm) in association to water and hydronium molecules, rather than forming a 3D network inside crystals. Overall findings indicate that APT can be an ideal technique to characterize intra-crystalline organic components in abiogenic and biogenic carbonates to further advance our understanding of biomineralization.
Highlights
Biomineralization is quite unique and different to inorganic mineralization, mainly because biominerals are composites of mineral and organic phases [1]
Transmission electron microscopy (TEM) tomography has proven to be a robust technique for this purpose (e.g., [7]), but the available information is limited to partial visualization of organic components without quantitative chemical data
Single calcite crystals were grown in the presence of chitin hydrogel and chitin nanofibers [6]
Summary
Biomineralization is quite unique and different to inorganic mineralization, mainly because biominerals are composites of mineral and organic phases [1]. Focusing on biominerals produced by invertebrates, in particular those with carbonate composition, two main organic components have been described: an inter-crystalline fraction present in-between structural units (i.e., prisms); and an intra-crystalline fraction, inside the mineralized structure (i.e., a prism or nacre tablet). Synthetic carbonate systems, especially single calcite crystals, have been used to study the incorporation of organic components (i.e., peptide or polysaccharides) and their effect on the formation of crystal defects, mechanical properties, and the incorporation of chemical impurities (e.g., [3,4,5,6]). Transmission electron microscopy (TEM) tomography has proven to be a robust technique for this purpose (e.g., [7]), but the available information is limited to partial visualization of organic components without quantitative chemical data. Confocal microscopy, in conjunction with fluorescent-labelled organics, has been used [5], yet with similar issues to those related to TEM tomography
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