Amphiphilic Nanoparticles Induce Membrane Capacitance and Tension Reductions in planar lipid membranes*

While amphiphilic gold nanoparticles (NPs) that have been modified with a striped arrangement of hydrophilic sulfonate and hydrophobic octanethiol (OT) ligands demonstrate potential for improved drug delivery due to their passive cellular uptake capabilities, precise methods by which they traverse biological membranes remain elusive. Herein, we utilize the planar lipid bilayer, which allows for subsequent electrophysiological characterization. Electrical measurements and image processing reveal that the utilization of NPs containing 15 mol% OT ligands leads to a reduction in the area-normalized capacitance and contact angle of the bilayer. The extent of this reduction is contingent upon the concentration of NPs employed in the experiment. When integrated with additional electrical data, this observed pattern suggests that these NPs exhibit a spontaneous tendency to insert themselves into the hydrophobic core of the bilayer, resulting in an overall increase in its average thickness and a decrease in its capacitance per unit area. In contrast, the introduction of hydrophilic NPs without hydrophobic ligands did not result in any noticeable alterations in the specific capacitance of the bilayer. This suggests that hydrophobic ligands play a crucial role in facilitating the incorporation of NPs into the bilayer. It was also observed that NPs with 30 mol% hydrophobic ligands exhibited more significant reductions in specific capacitance at a lower concentration of NPs, compared to ones with 15 mol% OT.