We have developed and applied a molecular theory that enables the investigation of the interactions between polyelectrolyte coated nanoparticles (NPs) in aqueous solutions. Potential applications of polyelectrolyte-coated NPs involve nanosensors for oil well characterization. To account for the high salinity environment encountered in an oil well or brine solution, we also considered in the theoretical description counterion condensation as well as ion-ion paring. We identified the design criteria to achieve dispersion stability of NPs coated with either polyacrylic acid (pAA), poly acrylamido-2-methylpropane sulfonate (pAMPS), or an alternating copoly-mer of acrylic acid and acrylamido-2-methylpropane sulfonate (pAA-a-AMPS) under brine-like conditions and quantified the effects of NP core size, molecular weight, density of the polyelectrolyte coating, and polymer chemistry. The results were summarized in stability diagrams, which predict the polymer surface coverage and molecular weight that is required for the NP solution to remain dispersed. (C) 2014 Wiley Periodicals, Inc.