Hyperspectral interference tomography of nacre

TL;DR

This paper introduces hyperspectral interference tomography (HIT), a rapid, non-destructive optical method for mapping the layered structure of nacre, revealing new insights into mollusk shell growth and environmental conditions.

Contribution

The paper presents a novel all-optical hyperspectral interference tomography technique for structural analysis of nacre, enabling large-area, non-destructive, and rapid characterization.

Findings

Mapped nacre layer thickness across entire shells

Discovered relationship between mollusk growth and tablet thickness

Demonstrated non-destructive imaging of layered materials

Abstract

Structural characterization of biologically formed materials is essential for understanding biological phenomena and their environment, and generating new bio-inspired engineering concepts. For example, nacre -- formed by mollusks in the ocean -- encodes local environmental conditions throughout its formation and has exceptional strength due to its nanoscale brick-and-mortar structure. This layered structure, comprising transparent aragonite tablets bonded with an ultra-thin organic polymer, also results in stunning interference colors. Existing methods of structural characterization of nacre rely on some form of cross-sectional analysis, such as scanning electron microscopy or polarization-dependent imaging contrast (PIC) mapping. However, these techniques are destructive and too time- and resource-intensive to analyze large sample areas. Here we present an all-optical, rapid, and non-destructive imaging technique -- hyperspectral interference tomography (HIT) -- to spatially map the structural parameters of nacre and other disordered layered materials. We combined hyperspectral imaging with optical-interference modeling to infer the mean tablet thickness and disordering of nacre layers across entire mollusk shells at various stages of development, observing a previously unknown relationship between the growth of the mollusk and tablet thickness. Our rapid, inexpensive, and nondestructive method can be readily applied to in-field studies.