Assembling mechanism of platinum nanoparticles into a {1 0 1} sectors of a tetragonal lysozyme crystal was examined for two different types of the platinum nanoparticles which have either positive or negative zeta potential at pH 3-7. The distribution coefficient of the positive ones inside the crystal is much higher than that of the negative ones in the whole pH range investigated. Dispersivity of the platinum nanoparticles before interaction with the lysozyme crystal surface, which is controlled by electrostatic interactions between nanoparticles, lysozyme and NaCl, causes a profound difference on the assembly of the nanoparticles into the crystal. (C) 2014 Elsevier B.V. All rights reserved.