Size Estimation of Biological Ink Particles Dispersed in Liquids Using Atomic Force Microscopy

The size distributions of size-controlled ink particles isolated from the ink sacs of squid and cuttlefish were studied by atomic force microscopy (AFM). Topological images indicated that the squid ink particles deposited on mica were not spherical but instead were hemisphere-like. From the heights and widths of the hemisphere-like structures on mica, the diameters of the squid ink particles dispersed in aqueous suspension were estimated to be approximately nm, close to that obtained from dynamic light scattering analysis. The estimated values were almost the same regardless of the spring constant of AFM cantilevers. A precise estimation was also achieved for the cuttlefish ink particles. The estimation method suggested in the present study would be a valid technique for precisely measuring the size distribution of biological particles by AFM.