Tension-Induced Translocation of an Ultrashort Carbon Nanotube through a Phospholipid Bilayer

Increasing awareness of bioeffects and toxicity of nanomaterials interacting with cells puts in focus the mechanisms by which nanomaterials can cross lipid membranes. Apart from well-discussed energy-dependent endocytosis for large objects and passive diffusion through membranes by solute molecules, other translocation mechanisms based on physical principles can exist. We show the importance of membrane tension on the translocation through lipid bilayers of ultrashort carbon nanotubes (USCNTs). By using a combination of a microfluidic setup and single chain mean field (SCMF) theory, we observed that, under membrane tension, USCNT inserted into a lipid bilayer may spontaneously nucleate an unstable local pore, allowing it to escape from the bilayer. We demonstrated that stretching of the membrane is essential for triggering this mechanism of translocation, and no translocation is observed at low membrane tension. For this purpose, a quantitative analysis of the kinetic pathway associated with USCNT translocation induced by tension was performed in a specially designed microfluidic device, simultaneously combining optical fluorescence microscopy and electrophysiological measurements. An important outcome of these findings is the identification of the way to control the nanomaterial translocation through the lipid bilayer by membrane tension that can be useful in many practical applications.