Electrolyte-Mediated Assembly of Charged Nanoparticles

Sumit Kewalramani, Guillermo Iván Guerrero-García, Liane M Moreau, Jos W. Zwanikken, Chad A Mirkin, Monica D Olvera, Michael J Bedzyk

Research output: Contribution to journalArticle

28 Scopus citations


Solutions at high salt concentrations are used to crystallize or segregate charged colloids, including proteins and polyelectrolytes via a complex mechanism referred to as “salting-out”. Here, we combine small-angle X-ray scattering (SAXS), molecular dynamics (MD) simulations, and liquid-state theory to show that salting-out is a long-range interaction, which is controlled by electrolyte concentration and colloid charge density. As a model system, we analyze Au nanoparticles coated with noncomplementary DNA designed to prevent interparticle assembly via Watson–Crick hybridization. SAXS shows that these highly charged nanoparticles undergo “gas” to face-centered cubic (FCC) to “glass-like” transitions with increasing NaCl or CaCl2 concentration. MD simulations reveal that the crystallization is concomitant with interparticle interactions changing from purely repulsive to a “long-range potential well” condition. Liquid-state theory explains this attraction as a sum of cohesive and depletion forces that originate from the interelectrolyte ion and electrolyte–ion–nanoparticle positional correlations. Our work provides fundamental insights into the effect of ionic correlations in the salting-out mechanism and suggests new routes for the crystallization of colloids and proteins using concentrated salts.
Original languageEnglish (US)
Pages (from-to)219-224
Number of pages6
JournalACS Central Science
Issue number4
StatePublished - 2016


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