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Growth of Anisotropic Gold Nanoparticle Assemblies via Liposome Fusion

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Growth of Anisotropic Gold Nanoparticle Assemblies via Liposome Fusion

Kouta Sugikawa et al. Materials (Basel).

Abstract

Anisotropic assembly of nanoparticles (NPs) has attracted extensive attention because of the potential applications in materials science, biology, and medicine. However, assembly control (e.g., the number of assembled NPs) has not been adequately studied. Here, the growth of anisotropic gold NP assemblies on a liposome surface is reported. Citrate-coated gold NPs adsorbed on liposome surfaces were assembled in one dimension at temperatures above the phase transition temperature of the lipid bilayer. Growth of the anisotropic assemblies depended on the heating time. Absorption spectroscopy and transmission electron microscopy revealed that the gradual growth was attributed to liposome fusion, which was strongly affected by the size of the gold NPs. This method enabled us to precisely control the number of NPs in each anisotropic assembly. These results will enable the fabrication of functional materials based on NP assemblies and enable investigations of cell functions and disease causality.

Keywords: anisotropic assembly; gold nanoparticles; lipid membrane; liposomes.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Time-dependent UV–vis absorption spectra of cAuNP14–DPPC solutions ([cAuNP]/[liposome] = 1.67) heated at 50 °C for 10 min to 7 days; (b) Plots of the absorbance at 605 nm (red squares) and the average number of cAuNPs in each assembly (X¯n, blue triangles) vs. heating time at 50 °C. TEM images of cAuNP14–DPPC; (c) before heating and after; (d) 10 min; (e) 1 h; (f) 24 h; (g) 3 days; and (h) 7 days heating at 50 °C. The scale bars are 100 nm.
Figure 2
Figure 2
Liposome diameters determined from cryo-TEM images (Figure S2). cAuNP14–DPPC (a) before and after (b) 1 day and (c) 7 days heating at 50 °C.
Figure 3
Figure 3
Cryo-TEM images of cAuNP31–DPPC ([cAuNP]/[liposome] = 1.67) heated at (a) 25 °C and (b) 50 °C; The scale bars are 100 nm; (c) UV–vis absorption spectra of solutions of cAuNP31 (black dashed line), cAuNP31–DPPC at 25 °C (red solid line), and cAuNP31–DPPC at 50 °C (blue solid line).
Figure 4
Figure 4
(a) Time-dependent UV–vis absorption spectra of cAuNP31–DPPC solutions ([cAuNP]/[liposome] = 1.67) heated at 50 °C for 10 min (red line), 24 h (orange line), 3 days (green line), and 7 days (blue line); Cryo-TEM images of cAuNP31–DPPC heated at 50 °C for (b) 10 min; (c) 24 h; and (d) 7 days. The scale bars are 100 nm.
Figure 5
Figure 5
Liposome diameters determined from the cryo-TEM images (Figure S3). DPPC liposomes heated at (a) 25 and (b) 50 °C for 24 h; (c) cAuNP14–DPPC and (d) cAuNP31–DPPC heated at 50 °C for 24 h.
Figure 6
Figure 6
Average number of cAuNPs in each assembly (X¯n) vs time. cAuNP14–DPPC composite solutions were cooled in an ice bath after heating at 50 °C for 10 min (red squares), 1 h (blue rhombuses), and 12 h (purple crosses). Blue triangles are X¯n for cAuNP14–DPPC composites heated for 3 days without cooling.

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