Use of solid-state nanopores for sensing co-translocational deformation of nano-liposomes

Abstract

Membrane deformation of nano-vesicles is crucial in many cellular processes such as virus entry into the host cell, membrane fusion, and endo- and exocytosis; however, studying the deformation of sub-100 nm soft vesicles is very challenging using the conventional techniques. In this paper, we report detecting co-translocational deformation of individual 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) nano-liposomes using solid-state nanopores. Electrokinetic translocation through the nanopore caused the soft DOPC liposomes (85 nm diameter) to change their shape, which we attribute to the strong electric field strength and physical confinement inside the pore. The experiments were performed at varying transmembrane voltages and the deformation was observed to mount up with increasing applied voltage and followed an exponential trend. Numerical simulations were performed to simulate the concentrated electric field strength inside the nanopore and a field strength of 14 kV cm(-1) (at 600 mV applied voltage) was achieved at the pore center. The electric field strength inside the nanopore is much higher than the field strength known to cause deformation of 15-30 μm giant membrane vesicles. As a control, we also performed experiments with rigid polystyrene beads that did not show any deformation during translocation events, which further established our hypothesis of co-translocational deformation of liposomes. Our technique presents an innovative and high throughput means for investigating deformation behavior of soft nano-vesicles.

Counting and Sizing of Single Vesicles/Liposomes by Electrochemical Events

“…Recently, researchers [36][37][38][61][62][63][64] have paid attention to the peculiarities of soft particles (e. g., vesicles/ liposomes) during pore/channel translocation events. This phenomenon presents a great challenge in the accurate determination of single-vesicle/liposome properties, especially size and surface charge.…”

“…Kim et al [61,62] investigated the deformation of liposomes with varying rigidity inside silicon nitride nanopores and observed a significant difference in resistive pulse current between soft liposomes and rigid polystyrene nanoparticles, especially at higher applied voltages ( Figure 1). Recently, researchers have studied the influences caused by such deformation on the size measurement and other characterizations of vesicles/liposomes during translocation.…”

Stiffness measurement of nanosized liposomes using solid‐state nanopore sensor with automated recapturing platform

“…The nanoscale vesicles, due to their extremely small size, present experimental challenges in sample preparation, concentration bounds, measurement optimization, and scanning throughput. In this paper, we suggest a new technique involving a label‐free, non‐destructive, high throughput, single particle sensing solid‐state nanopore platform with recapturing capability to overcome difficulties associated with classical methods.…”

“…A nanopore is a single molecule sensor that can capture molecular level information of nanoparticles by reading very low electrical current perturbations in real time characterized by duration (Δ t ), i.e., translocation time, and the magnitude of the current drop (Δ I ), i.e., current blockade, as charged nanoparticles translocate across the nanopore. Nanopores are used to detect and analyze various biomolecules, such as DNA , proteins , polysaccharides , virus particles , and liposomes , and non‐biomolecules, such as polystyrene beads and gold nanoparticles . In most instances, particle deformation is neglected.…”

“…In most instances, particle deformation is neglected. In the case of nanoscale soft matter (e.g., endosomes, exosomes, viruses, and artificial liposomes), the shape deformation occurs within the nanopore as a result of the strong electric field within the nanopore, the hydrodynamic drag force ( F d ) opposing the electrophoretic transit, and the flexibility of the material . Since both the baseline current ( I 0 ) and Δ I increase proportionally with voltage, if there is no deformation, the relative current blockade () would remain constant—independent of the magnitude of the applied voltage .…”