Creation and regulation of ion channels across reconstituted phospholipid bilayers generated by streptavidin-linked magnetite nanoparticles

In this work, we explore the nature of ion-channel-like conductance fluctuations across a reconstituted phospholipid bilayer due to insertion of ∼100 nm sized, streptavidin-linked magnetite nanoparticles under static magnetic fields (SMFs). For a fixed bias voltage, the frequency of current bursts increases with the application of SMFs. Apart from a closed conductance state $G_0$ (≤14 pS), we identify four major conductance states, with the lowest conductance level ($G_1$) being ∼126 pS. The number of channel events at $G_1$ is found to be nearly doubled (as compared to $G_0$) at a magnetic field of 70 G. The higher-order open states (e.g., 3$G_1$, 5$G_1$) are generally observable at larger values of biasing voltage and magnetic field. When the SMF of 145 G is applied, the multiconductance states are resolved distinctly and are assigned to the simultaneous opening and closing of several independent states. The origin of the current bursts is due to the instantaneous mechanical actuation of streptavidin-linked MNP chains across the phospholipid bilayer. The voltage-controlled, magnetogated ion channels are promising for diagnoses and therapeutic applications of excitable membranes and other biological systems.

Figure 1

(a) An optical micrograph of a stable bilayer suspended over a ∼95 μm diameter glass aperture. (b) Dynamic light scattering response of MNP size distribution. (c) A scheme of the experimental setup: lipid bilayer formation and streptavidin-linked MNP injection into electrolytic chamber. (d) Streptavidin-linked MNP chains hitting the bilayer surface momentarily (not to scale). (e) Noise current before and after MNP injection.

Figure 2

Typical ion-channel traces recorded in the presence of SMFs: (a) 8 G, (b) 70 G, and (c) 145 G. All of the current bursts were recorded at a biasing voltage of –90 mV. Note the remarkable evolution of multiconductance states 3$G_1$, 5$G_1$, etc.

Figure 3

Statistical analysis (event histograms) of current bursts in the (a) absence and presence of magnetic fields of strength (b) 70 G, and (c), (d) 145 G. In series (a-d), the Gaussian fits used to identify different conductance states are represented by dotted lines, and symbol ‘p’ that appear along abscissa basically represent pico-order magnitude. Magnetic field and voltage dependent channel events of $G_1$, as compared to $G_0$, are shown in (e) and (f); respectively. In (e), the labels $\blacksquare ,•,▴$, and $▾$ correspond to −30, −50, −70, and −90 mV; respectively. (A full set of histograms is available in the Supplemental Material, see Ref. [14].)

Figure 4

Optical micrograph of MNPs in electrolytic buffer: in the (a) absence and (b) presence of a SMF (145 G) due to application of Q magnets. The chainlike MNP aggregation is evident in case (b). The dark red contrast is due to agitated MNPs in the buffer solution.

Figure 5

Room temperature magnetic measurements of MNPs. Magnetization ($I$) vs applied field ($H$) plot of streptavidin linked MNPs used in the experiment. The volume susceptibility (χ) was estimated from the linear response of $I$ vs $H$ (inset) in the low field range.