Effective Surface Charge Density Determines the Electrostatic Attraction between Nanoparticles and Cells

We examine the origin of the electrostatic attraction between nanoparticle (NP) and cells by synthesizing a NP array with a continuous change in surface charge density (SCD). This attraction does not show a linear and continuous change, but a sharp increase as the positive SCD increases. The results of zeta potential measurements of the naked and protein bound NPs reveal that excessive charges on surface ligands are partially shielded, and the noncovalent protein bindings do not influence NP cell electrostatic interactions. The effective SCD on the outmost layer of NPs determined the electrostatic attraction between NPs and cells