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To detect trace molecules within giant unilamellar vesicles (GUVs), the effect of surface-enhanced Raman scattering within the vesicles was examined. Enhanced Raman spectra of a target molecule (bipyridine) within the GUVs were acquired through the encapsulation of gold nanoparticle aggregates and bipyridine. Furthermore, the introduction of gramicidin into the GUV membrane facilitated cation permeation through the lipid membrane, regulating the aggregation of gold nanoparticles. While the encapsulation of the gold nanoparticle dispersion in the GUV did not enhance the Raman signal, aggregation of gold nanoparticles, triggered by the influx of Na+ ions via gramicidin, amplified the Raman spectrum. This observation implies that molecules integrated into GUVs through vesicle fusion can aggregate with gold nanoparticles. These gold nanoparticle-encapsulated GUVs could serve as a new biosensor for detecting small amounts of molecules within the vesicles.

Abstract Changes in the diffusion coefficient of supported lipid bilayers affected by their interaction with the substrate were evaluated by fluorescence recovery after photobleaching under different surface charges and ambient conditions (presence of divalent ions in solution). The diffusion coefficients of each leaflet were estimated separately by quenching only the leaflet on the far side from the substrate with Co²⁺ ions. The potential valleys, which are created by the divalent ions between the supported lipid bilayer and the substrate or the positive charges on the substrate surface, act as diffusion barriers, and the diffusion coefficient of the leaflet on the side closer to the substrate decreases. At the same time, the other leaflet far from the substrate also showed a somewhat decrease in diffusion coefficient due to interleaflet coupling.