Resistive-Pulse Detection of Multilamellar Liposomes

The resistive-pulse method was used to monitor the pressure-driven translocation of multilamellar liposomes with radii between 190 and 450 nm through a single conical nanopore embedded in a glass membrane. Liposomes (0% and 5% 1,2-dioleoyl-<i>sn</i>-glycero-3-phospho-l-serine (sodium salt) in 1,2-dilauroyl-<i>sn</i>-glycero-3-phosphocholine or 0%, 5%, and 9% 1,2-dipalmitoyl-<i>sn</i>-glycero-3-phospho­(1′-<i>rac</i>-glycerol) (sodium salt) in 1,2-dipalmitoyl-<i>sn</i>-glycero-3-phosphocholine) were prepared by extrusion through a polycarbonate membrane. Liposome translocation through a glass nanopore was studied as a function of nanopore size and the temperature relative to the lipid bilayer transition temperature, <i>T</i>_c. All translocation events through pores larger than the liposome, regardless of temperature, show translocation times between 30 and 300 μs and current pulse heights between 0.2% and 15% from the open pore baseline. However, liposomes at temperatures below the <i>T</i>_c were captured at the pore orifice when translocation was attempted through pores of smaller dimensions, but squeezed through the same pores when the temperature was raised above <i>T</i>_c. The results provide insights into the deformation and translocation of individual liposomes through a porous material