Amphiphilic gold nanoparticles (AmNPs) functionalized via a striped pattern of hydrophilic sulfonate and hydrophobic octanethiol ligands are promising for improved drug delivery since their amphiphilic nature enables them to enter cells passively. Yet details of these events remain elusive, in part because of insufficient experimental methods. The droplet interface bilayer (DIB) method for assembling a lipid bilayer between lipid-coated water droplets in oil offers advantages that could help reveal NP-membrane interactions, including control of droplet, and thus bilayer leaflet, compositions and membrane area and the ability to perform electrophysiology to monitor changes in bilayer structure and transport properties. The challenge to enable DIBs for studying NP-membrane interactions is to incorporate NP into the droplets after bilayer formation since AmNPs and lipids co-assembling at the droplet surface has shown to destabilize the bilayer during formation.<br/><br/>Herein, we present direct injection of AmNPs into DIB droplets <i>after</i> bilayer formation and use it to study changes in membrane properties exposed to AmNPs. Specifically, DIBs are formed by connecting a pair of ~400 nL droplets coated in diphytanoyl phosphatidylcholine lipids in hexadecane oil. The aqueous buffer containing AmNPs at a known concentration is injected into one droplet of a DIB using a pulled micropipette whose pressure is controlled by a pneumatic injector. The amount of AmNP solution injected is governed by the level and duration of applied pressure and the tip diameter of the pipette. Electrical measurements made via wire-type electrodes inserted into the droplets are used to assess bilayer formation prior to injection and quantify changes, specifically changes in resistance, capacitance, and membrane area in response to applied voltage in the DIB, during and after AmNP injection. These data along with other physical changes will be used to identify the mechanisms behind the passive interactions between AmNPs and lipid membranes.

Post bilayer formation direct injection for studying nanoparticle-membrane interactions in droplet interface bilayers

ACS Spring 2022

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