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Anchoring poly(ethylene glycol) (PEG) to inorganic nanoparticles (NPs) permits control over NP properties for a variety of technological applications. However, the core-shell structure tremendously complicates the interpretation of the ubiquitous ζ-potential, as furnished by electrophoretic light-scattering, capillary electrophoresis or gel electrophoresis. To advance the ζ-potential-and the more fundamental electrophoretic mobility-as a quantitative diagnostic for PEGylated NPs, we synthesized and characterized Au NPs bearing terminally anchored 5 kDa PEG ligands with univalent carboxymethyl end groups. Using the electrophoretic mobilities, acquired over a wide range of ionic strengths, we developed a theoretical model for the distributions of polymer segments, charge, electrostatic potential, and osmotic pressure that envelop the core: knowledge that will help to improve the performance of soft NPs in fundamental research and technological applications.

Improved control over protein nucleation is important to advance the design and operation of protein separation and purification processes. The influence of nonuniform electric fields induced by patterned indium tin oxide (ITO) electrodes of various shapes and surface areas on protein nucleation in microfluidic devices with parallel electrodes is investigated experimentally. In particular, the impact of various electrode designs and electric-field properties on the solid-state form, induction time, nucleation rate, and the location of lysozyme crystals is described. The results demonstrate that both enhanced and inhibited protein crystallization can be observed depending on the specifics of electrode shape and surface area and electric-field properties. The nucleation location of crystals is found to be influenced by both the ITO layer as a template and the nonuniform electric field induced by specific designs of electrodes. The optimal electric-field conditions and electrode design for enhancement of lysozyme crystallization could be extended to insulin crystallization experiments, which showed the formation of an insulin crystal near the electrode, whereas control experiments did not show any crystals.