We measured the conductance of bilayer lipid membranes of diphytanoylphosphatidylcholine induced by interaction with cubic magnetic nanoparticles (MNPs) of cobalt ferrite 12 and 27 nm in size and coated with a hydrophilic shell. The MNP coating is human serum albumin (HSA) or polyethylene glycol (PEG). The interaction of nanoparticles added to the bulk solution with the lipid bilayer causes the formation of metastable conductive pores, which, in turn, increases the integral conductance of the membranes. The increase in conductance with increasing MNP concentration was practically independent of the particle size. The dependence of the bilayer conductance on the concentration of PEG-coated MNPs was much weaker than that on the concentration with a shell of HSA. Analyzing the current traces, we believe that the conductive pores formed as a result of the interaction of nanoparticles with the membrane can change their size, remaining metastable. The form of multilevel current traces allows us to assume that there are several metastable pore states close in energy. The average radius of the putative cylindrical pores is in the range of 0.4–1.3 nm.

The study of the electrical parameters of asolectin bilayer lipid membranes in the presence of cytochrome c (cyt c) at various concentrations showed that an increase in the concentration of cyt c leads to an increase in the membrane conductance and the appearance of through pores. The studied membranes did not contain cardiolipin, which is commonly used in studying the effect of cyt c on membrane permeability. In the presence of cyt c, discrete current fluctuations were recorded. The occurrence of these fluctuations may be associated with the formation of through pores. The diameter of these pores was ~0.8 nm, which is smaller than the size of the cyt c globule (~3 nm). Measurements carried out at pH values from 6.4 to 8.4 showed that the concentration dependence of the membrane conductance increases with increasing pH. To assess the binding of cyt c to the bilayer, we measured the concentration and pH dependences of the difference in surface potentials induced by the unilateral addition of cyt c. The amount of bound cyt c at the same concentrations decreased with increasing pH, which did not correspond to the conductance trend. An analysis of conductance traces leads to the conclusion that an increase in the integral conductance of membranes is associated with an increase in the lifetime of pores. The formation of “long-lived” pores, of which the residence time in the open state is longer than in the closed state, was achieved at various combinations of pHs and cyt c concentrations: the higher the pH, the lower the concentration at which the long-lived pores appeared and, accordingly, a higher conductance was observed. The increase in conductance and the formation of transmembrane pores are not due to the electrostatic interaction between cyt c and the membrane. We hypothesize that an increase in pH leads to a weakening of hydrogen bonds between lipid heads, which allows cyt c molecules to penetrate into the membrane. This disrupts the order of the bilayer and leads to the occurrence of through pores.

The effect of pluronics L61 and F68 containing hydrophobic poly(propylene oxide) blocks of the same length and hydrophilic poly(ethylene oxide) blocks of different lengths on the conductance of planar bilayer lipid membranes made of azolectine is investigated. The conductance of these membranes increases as the concentration of both pluronics increases. For the same concentration of pluronics in solution, the conductance is higher for L61. Based on the literature data, the concentration of pluronics bound with the bilayer is calculated. For the close concentration of membrane-bound pluronics, the conductance of membranes is also close. It is concluded that in the first approximation, the appearance of the same hydrophobic parts of pluronics L61 and F68 in a membrane is accompanied by the same increase in its conductance. The conductance vs. concentration curves are superlinear for L61 and sublinear for F68. In the presence of either of these pluronics, the conduction spikes with the amplitude from 10 to 300 pSm and higher are observed for approximately 40% of membranes. These surges of conductance are associated with the appearance of conductive pores or defects in the membrane. The number of pores observed in the membrane is a random variable with a large scatter and does not correlate with the pluronic concentration. The difference between the average pore conductivities for membranes containing L61 and F68 is statistically insignificant.

This study investigates the mechanisms of interaction between superparamagnetic magnetite nanoparticles (MNPs) and a lipid bilayer membrane (BLM). Ligand-free polar magnetite nanoparticles, which form a colloidal suspension in the aqueous phase, can penetrate the BLM without compromising its integrity. As magnetite MNPs pass through the membrane, complexes of the nanoparticles with lipid molecules are formed, which are detected in the aqueous phase behind the membrane. In this study, independent experimental methods of structure-functional diagnostics, including FTIR spectroscopy, dynamic light scattering, scanning transmission electron microscopy (STEM), and energy-dispersive X-ray (EDX) spectroscopy, were used to characterize nanocomposite complexes adsorbed on novel magnetic traps installed behind a planar azolectin BLM. The obtained results indicate that the resulting complexes are polydisperse with characteristic sizes in the range of 10–300 nm and have an iron-containing core surrounded by a lipid shell in the form of bilayers or multilayers of lipid molecules. Using the Langmuir-Blodgett method, the interaction of colloidal magnetite MNPs in the aqueous phase with lipid azolectin monolayers on the surface of the aqueous subphase in an external nonuniform magnetic field was studied. The corresponding monolayer Langmuir films, deposited on a solid mica substrate using the Schaeffer and Langmuir-Blodgett methods, were studied by atomic force microscopy (AFM) in tapping mode. The results of a topographic analysis of the structure of the obtained nanocomposite Langmuir films containing complexes of magnetite nanoparticles and azolectin molecules are consistent with the above-mentioned structural analysis of nanocomposite complexes formed during the interaction of magnetite nanoparticles with a bilayer lipid membrane.

The changes of electrical parameters of azolectin membranes in a static inhomogeneous magnetic field at the one-sided addition of positively charged quasi-spherical superparamagnetic magnetite nanoparticles (MNPs) with a diameter of about 4 nm were studied. The magnet was located at different distances from the membrane, and nanoparticles were attracted to the membrane surface with different strengths by the magnetic field. After the addition of MNPs, a decrease in capacitance, polarization, and further depolarization of the membranes was observed. Zero current appeared on the bilayer lipid membranes (BLMs). There was no unambiguous dependence of the zero current on the membrane depolarization and there were no dependences of the zero current on the strength of the magnetic field and on the concentration of added MNPs. The membrane conductivity increased on average with an increase in the external magnetic field and depended on the ionic strength. Magnetic field caused a rapid accumulation of MNPs on the surface of the BLMs. As a result, the membrane was polarized. Depolarization of the membranes occurred when MNPs passed through the BLMs. The increase in conductivity reflected the processes of lipid bilayer disordering.