Gold nanoparticles (GNPs) are widely used in biological and clinical applications due to their favorable chemical and optical properties. GNPs can be used for drug delivery to targeted cells. In addition, GNPs serve as ideal probes for biological and cell imaging applications. Recent studies indicate that the size diversity of GNPs plays an important role in targeting cellular components for biomedical applications. In this study, we conducted a series of studies using different sizes of gold nanoparticles, including 3, 10, 25, and 50 nm, to determine the effect of size variations on their intracellular localizations. Our cytotoxicity studies of GNPs into the HEp-2 cells using MTT assay indicated that 3 nm GNPs possess the highest toxicity. We exposed HEp-2 cells with various sizes of gold nanoparticles for different time intervals (1, 2, 4, 12, and 24 h) followed by imaging using scanning electron microscope (SEM) and atomic force microscope (AFM). Our SEM and AFM results showed that, after 1 hr incubation, 3 and 10 nm gold nanoparticles entered the nucleus, whereas 25 and 50 nm particles accumulated around the nucleus. As the time of exposure increased, GNPs entered the cells and accumulated in the cytosol and nucleus based solely on their sizes.

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A modified PAMPA (parallel artificial membrane permeability assay) is proposed for evaluating the passive cuticular membrane permeability of potassium in several foliar nutrient formulations. The modified PAMPA can measure the passive permeability of ionic nutrients under fully hydrated conditions through an artificial membrane designed to more closely resemble a plant cuticle, rather than the traditional phospholipid animal model. Foliar nutrient formulations, which in some cases contain a complex organic matter component, may be evaluated with the modified PAMPA in order to develop better structure activity relationships that can help guide rational formulation development. In addition, mechanistic insights may also be uncovered with the simplified system.

In nanoparticle haloing, charged nanoparticles have been found to enhance the stability of colloidal suspensions by forming a non-adsorbing layer surrounding neutral colloids which induces an electrostatic repulsion between them. However, there has been some debate that nanoparticles may directly deposit onto the colloidal surfaces and that the stabilization mechanism relies on nanoparticle adsorption. In this study, we have found that these two mechanisms control the stability of colloidal suspensions across a continuum over increasing nanoparticle concentrations.AFM force measurements showed that highly charged zirconia nanoparticles built up an electrostatic repulsion between negligibly charged silica surfaces, preventing them from aggregating. The follow-up adsorption measurements and force modeling indicated that minor adsorption of nanoparticles is expected at volume fractions of 10 -5 to 10 -3 , but the amount of nanoparticle adsorption dramatically increases with increasing the nanoparticle volume fraction beyond 10 -3 . Based on these results, we propose that the fundamental mechanism of nanoparticleregulated stabilization is nanoparticle haloing at low nanoparticle concentrations which transitions to adsorption at higher concentrations. Accordingly, at a nanoparticle volume fraction of around 10 -3 where the transition happens, the stabilization can be influenced by both nanoparticle haloing and adsorption.