Disruption of Model Cell Membranes by Carbon Nanotubes

Abstract

Carbon nanotubes (CNTs) have one of the highest production volumes among carbonaceous engineered nanoparticles (ENPs) worldwide and are have potential uses in applications including biomedicine, nanocomposites, and energy conversion. However, CNTs possible widespread usage and associated likelihood for biological exposures have driven concerns regarding their nanotoxicity and ecological impact. In this work, we probe the responses of planar suspended lipid bilayer membranes, used as model cell membranes, to functionalized multi-walled carbon nanotubes (MWCNT), CdSe/ZnS quantum dots, and a control organic compound, melittin, using an electrophysiological measurement platform. The electrophysiological measurements show that MWCNTs in a concentration range of 1.6 to 12 ppm disrupt lipid membranes by inducing significant transmembrane current fluxes, which suggest that MWCNTs insert and traverse the lipid bilayer membrane, forming transmembrane carbon nanotubes channels that allow the transport of ions. This paper demonstrates a direct measurement of ion migration across lipid bilayers induced by CNTs. Electrophysiological measurements can provide unique insights into the lipid bilayer-ENPs interactions and have the potential to serve as a preliminary screening tool for nanotoxicity.

Figure 1

Schematic of the experimental setup for electrophysiological measurements on pBLM. The ion migration across the bilayer is monitored using a low-noise amplifier and Ag/AgCl electrodes. A lipid bilayer is suspended across a 150-μm polystyrene aperture that separates the cis and trans well. ENPs (shown here as MWCNT) are added to the cis-well and disrupt the bilayer and results in an increase in the measured electrical current.

Figure 2

Current-time traces of the and normalized current histograms with DOPC lipid bilayers at pH = 7.4 (20 mM HEPES and 20 mM KCl). (A) absence of nanoparticles; (B) melittin, a well-known pore forming peptide on lipid bilayers, at 6 ppm; (C) carboxyl quantum dots at 6 ppm; (D) functionalized multi-walled carbon nanotubes at 6 ppm.

Figure 3

Fractional event interaction of QD, MWCNT, and melittin with DOPC lipid bilayers at pH = 7.4 (20mM HEPES and 20mM KCl) at several nanoparticle concentrations. The fraction event interaction is a quantitative measure of the fraction of time that the nanomaterials disrupt the bilayer. The FEI increases with concentration and varies with particle composition and shape.

Figure 4

Average conductance induced by QD, MWCNT, and melittin on DOPC lipid bilayers at pH = 7.4 (20mM HEPES and 20mM KCl) at several particle mass concentrations. The average conductance is calculated excluding the background signal.