Morphologies of eumelanins from the ink of six cephalopods species measured by atomic force microscopy

The morphologies of eumelanin, isolated from the six cephalopods species Sepia esculenta, Sepia lycidas, Sepia pharaonis, Sepiella japonica, Euprymna berryi, and Uroteuthis (Photololigo) edulis, were investigated using atomic force microscopy (AFM). The results showed that the hierarchical aggregate structures of irregular spherical particles with different diameters are the common characteristics of these eumelanins. Furthermore, the diameters of these spherical particles present an uneven distribution in a wide range and mainly concentrate in the range of about 20-150 nm. In addition, the eumelanin from different cephalopods species show obvious differences in the morphologies, which is illustrated by different assembly forms of diverse aggregate units and the quantitative features of eumelanin particles derived from the images.