Analysis of tissue condition based on interaction between inorganic and organic matter in cuttlefish bone

The absorption properties of an inner layer of cuttlefish bone were measured using a transmission terahertz time-domain spectrometer in a band from approximately 0.1 to 4 THz. For oriented samples, an absorption peak related to the behavior of calcium carbonate appeared at approximately 2 THz. The peak magnitude and frequency depended on the direction of the incident terahertz electric field, indicating that calcium carbonate crystals constituting the inner layer were oriented in a certain direction. The absorbance of a sample heated to 350 °C for 0 to 2 h to remove organic matter tended to decrease with heating time in the oriented direction, while the peak frequency shifted to higher frequencies. Furthermore, we showed that the peak frequency depended on the interaction area within the unheated sample and we thus obtained a two-dimensional image reflecting crystal regularity inside the cuttlefish bone from the spectral data at each position.