Magnetoliposomes as model for signal transmission

Abstract

Liposomes containing magnetic nanoparticles (magnetoliposomes) have been extensively explored for targeted drug delivery. However, the magnetic effect of nanoparticles movement is also an attractive choice for the conduction of signals in communication systems at the nanoscale level because of the simple manipulation and efficient control. Here, we propose a model for the transmission of electrical and luminous signals taking advantage of magnetophoresis. The study involved three steps. Firstly, magnetite was synthesized and incorporated into fusogenic large unilamellar vesicles (LUVs) previously associated with a fluorescent label. Secondly, the fluorescent magnetite-containing LUVs delivered their contents to the giant unilamellar vesicles (GUVs), which were corroborated by magnetophoresis and fluorescence microscopy. In the third step, magnetophoresis of magnetic vesicles was used for the conduction of the luminous signal from a capillary to an optical fibre connected to a fluorescence detector. Also, the magnetophoresis effects on subsequent transmission of the electrochemical signal were demonstrated using magnetite associated with CTAB micelles modified with ferrocene. We glimpse that these magnetic supramolecular systems can be applied in micro- and nanoscale communication systems.

Keywords: giant unilamellar vesicles; large unilamellar vesicles; nanoparticulated magnetite; signal transmission.

Figure 1.

Versatility for the use of the delivery of particles and fluorophores to GUVs for the transmission of signals.

Figure 2.

Characterization of synthesized magnetite nanoparticles. (a) Representative SEM image, (b) particle size distribution, (c) XRD pattern and (d) magnetization curve.

Figure 3.

Analysis of Fe₃O₄/PC/CL composition. (a) FTIR spectra of bare and LUV-encapsulated magnetite nanoparticles. The black line corresponds to the spectrum of bare magnetite, the blue line to PC/CL-encapsulated magnetite. The insets show snapshots of temporal movement of magnetite in aqueous suspension (lower insets) and lipid-coated magnetite (upper insets) under the action of a magnet. The encapsulation by lipids delays the movement of the nanoparticles. The times are indicated in the snapshots. (b) FESEM images and energy dispersive X-ray spectroscopy (EDX) maps/spectrum. The elemental maps of oxygen (blue), iron (red) and carbon (yellow) are indicated in the respective panels. In two areas of the oxygen and iron maps, which are delimited by the yellow dashed squares, the higher oxygen density relative to that of iron is consistent with the contribution of oxygen in magnetite nanocrystals (crystalline structure at the right side of the figure) and POPC and TOCL (three-dimensional structures at the left side of the figure) that as expected should occupy a higher area than magnetite. The higher density areas of carbon signal are coincident with those of oxygen and iron. Concerning EDX limitation for the detection of low atomic number elements, the comparison of the carbon signal with the signals of oxygen and iron is merely qualitative. The smooth, bright areas of the image correspond to crystallization of KCl. The K⁺ and Cl⁻ are the counter ions of ammonium quaternary and phosphate groups of PC structure that crystallizes when the sample is dried for analysis. The acceleration voltage used for EDX analysis was 10 kV.

Figure 4.

Fusion of LUVs with GUVs detected by fluorescence. (a) and (b) are, respectively, the phase-contrast and fluorescence images of GUVs devoid of fluorescent dyes after fusion with LUVs carrying MC540. (c) and (d) are, respectively, the phase-contrast and fluorescence images of GUVs devoid of fluorescent dyes after fusion with LUVs carrying MC540 and magnetite.

Figure 5.

Optical microscopy images showing magnetophoresis of GUVs fused with LUVs loaded with magnetite in a condition like that described in figure 4. (a) Five GUVs are identified by the letters a, b, c, d and e followed by the subscript indices i (initial position) and f (final position) in time-lapsed images. The plot of magnetic force which is proportional to drag force versus GUV radius (blue points) was linearly fitted at two data intervals revealing different slopes for the GUV population with radii of 1.1–1.6 µm and 2.0–4.0 µm. (b) is an out-of-scale cartoon representing GUV magnetophoresis promoted by magnetite attached inside the lipid bilayers observed in (a) and GUV deformation by internal free magnetite under the action of a magnetic force that was not observed in the present study.

Figure 6.

Magneto electrochemistry of Fe₃O₄-CTAB-Fc. The electroactivity was determined in the ‘switch off’ (red line) ‘switch on’ (green line) modes in the configuration I of Melo et al. [45]. (a) Cyclic voltammograms of Fe₃O₄-CTAB-Fc at 100 mV s⁻¹ obtained at ‘switch on’ (green line) and ‘switch off’ modes (black line). The anodic (j_pa) and cathodic (j_pc) peaks as a function of the scan rates^1/2 obtained in the ‘switch off’ (red points) and ‘switch on’ (green points) modes, respectively. The grey line corresponds to the voltammogram of ferrocene associated with CTAB micelles (control). Support electrolyte: 0.1 mol l⁻¹ KCl, pH 7.0. (b) A possible organization of the supramolecular material Fe₃O₄-CTAB-Fc is shown in the scheme of the magneto electrochemistry configuration.

Figure 7.

The switchable light signals by magnetophoresis. (a) shows the fluorescence of GUVs that were loaded with MC540 and magnetite and had magnetophoretic properties. The capillary tube containing GUVs is in close contact with an optical fibre delivering the excitation laser. The fluorescence emission spectra of GUVs were transmitted by the optical fibre, and the spectrum could be recorded as shown in (b). In (b), the grey line corresponds to the signal of non-fluorescent GUVs and the black line to the spectrum of MC540 associated with GUVs.