Charged and Neutral Au Nanoparticles Interact Differently with Langmuir Film-Based Synthetic Membranes: Implications for Nanoparticle Uptake and Membrane Protein Activity

The safe and effective use of nanoparticles for biological applications requires a many-pronged classification of nanoparticle properties (material, coating, size, and shape) as well as biological environments. A Langmuir-film-based synthetic membrane system containing an active transmembrane protein, glucose-6-phosphatase (G6Pase), was employed to investigate the effects nanoparticle exposure as a function of membrane surface pressure. The activity of G6Pase after exposure to 5 nm gold nanoparticles functionalized with anionic, cationic, and neutral ligand coatings was found to increase by as much as 300% for both anionic and neutral particles at surface pressures less than 30 mN/m, indicating significant nanoparticle–protein interactions. Atomic force microscopy imaging was used to track the distribution of nanoparticles and G6Pase within the membranes and correlate changes in activity to the distribution of G6Pase in the membrane. Conditions which enabled the redistribution of protein in the form of solubilization or aggregation within the membrane were identified for each class of nanoparticles. This investigation demonstrates the importance of the phospholipid environment surrounding membrane proteins during exposure to nanoparticles which can impact the nanoparticle fate in terms of uptake as well as potential effects on membrane protein activity.