Quantifying the Effect of Detergent on Interactions between Nanoparticles and a Model Cell Membrane

Abstract

Due to their small size, nanoparticles (NPs) have the ability to penetrate cell membranes, and are therefore classified as potential human carcinogens. NP insertion into targeted cells also proves beneficial for drug delivery and gene therapy applications, prompting a need to more thoroughly characterize NP/membrane interactions. Polystyrene NPs with modifications in size, surface functionalization and detergent conditions were introduced to a Langmuir lipid monolayer of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), a model of the outer leaflet of the cell membrane. At bilayer equivalent pressure, aminated and carboxylated NPs showed appreciable monolayer insertion whereas plain NPs solubilized the phospholipid layer, removing it from the air/water interface. Detergent added to a NP solution typically prevents particle aggregation, but the amphiphilic character of surfactant may also affect cell membrane interactions. Detergent-free NP solutions interact differently compared to those containing detergent, resulting in monolayer destruction. To examine the role of charged detergents, sodium dodecyl sulfate (SDS) and dodecyl trimethyl ammonium bromide (DTAB) surfactants were introduced. Solutions composed of surfactant and NP functionalized with groups of the same charge showed appreciable interactions with the monolayer. Solutions of NPs and surfactants with opposing functional group charge aggregated, preventing authentic interactions. NP solutions with a higher concentration (1 wt%) of detergent initially showed increased insertion into the monolayer, suggesting cooperative behavior between NP and surfactant. The behavior of these NPs with the monolayer has two distinct regimes - an initial insertion event followed by monolayer destruction which is suggestive of interplay between kinetic and thermodynamic control.