Effect of Buffer Types and Their Concentrations on zeta Potentials of Positively Charged Nanoparticles

Huang, YX (Huang, Yun-xiao)^[ 1 ] ; Yan, HS (Yan, Hu-sheng)^[ 1,2 ]

ACTA POLYMERICA SINICA, 2018, 7: 893-899

DOI: 10.11777/j.issn1000-3304.2018.18007

 WOS:000446262600011

Abstract

The application of charged nanoparticles in drug delivery and imaging has been extensively investigated. The surface charge density of charged nanoparticles, which is usually characterized by zeta potentials, has a drastic effect on the interaction between the nanoparticles and the biological systems, and this interaction is critical for the in vivo biofate of the nanoparticles. However, the effect of different types of buffer systems and their concentrations on the zeta potentials is often ignored in literature. Various buffer systems, such as phosphate, Tris, Hepes and Mops, and different buffer concentrations from 1 mmol/L to 200 mmol/L, were used for measuring zeta potentials of nanoparticles. Herein the effect of buffer types and their concentrations on the zeta potentials for three different types of amine group-containing nanoparticles, i.e. poly(amido amine) (PAMAM) dendrimer, polystyrene-block-poly((N,N-diethylamino)ethyl methacrylate) (PS-b-PDMAEMA) micelles and chitosan nanoparticles, was studied. The zeta potentials of all the three types of nanoparticles decreased in the order of Tris, Hepes, Mops, and phosphates for buffer systems at the same concentration and pH. The potentials were much lower in phosphate buffer than that in the others. The zeta potentials of amino group-containing chitosan nanoparticles showed even negative values in phosphate buffer with the concentration below similar to 10 mmol/L at pH = 7.4. The zeta potentials of all the three types of nanoparticles drastically decreased with the increase in buffer concentration (from 2 mmol/L to 100 mmol/L) for all the buffer systems investigated. The zeta potentials of chitosan nanoparticles in phosphate buffer (pH = 7.4) were reversed from positive to negative with the increase in phosphate concentration, with the crossover concentration of around 10 mmol/L. This charge reversal was contributed to the low protonation degree of chitosan amino groups (pK(a) = 6.3) at pH = 7.4, and the presence of trivalent phosphate anions, which should be strongly adsorbed onto the positively charged particle surfaces and subsequently shielded the positive charges. When NaCl was added in the buffers, the zeta potentials of all the three types of nanoparticles decreased with increasing concentrations of the salt.