Accurate size determination of polystyrene latex nanoparticles in aqueous media using a particle tracking analysis method

Abstract

The size determination of nanoparticles in aqueous solution is important in bio- and nanotechnology. The sizes of particles in aqueous solution are determined by particle tracking analysis (PTA) with the Stokes–Einstein assumption from diffusion coefficient measurements. However, the interactions between particles affect the particle size determined by PTA. In this work, we observed particle/electrolyte concentration-dependent change in the apparent size of polystyrene (PS)-latex particles. Based on the Derjaguin, Landau, Verwey, and Overbeek theory, the change in the observed size of PS-latex particles estimated by PTA in various aqueous electrolyte solutions is caused by the long-range electrostatic interactions between the particles. Accurate size determination of PS-latex particles in aqueous solution was performed after reduction of the electrostatic interaction between particles by varying both the concentrations of the PS-latex particles and the electrolyte in aqueous solution. Zeta potential measurement and DLVO assessment gave a good indicator to reduce the electrostatic interactions between the particles for determination of accurate size of particle by PTA method. The proposed approach makes it possible to compare the determined sizes of various nanoparticles in the liquid-phase by PTA to those obtained by differential mobility analysers in the gas-phase. Although the determined sizes of nanoparticles using different sizing methods are difficult to compare, our investigation would allow researchers to achieve some degree of concordance on the size of nanoparticles using different sizing methods.