Effect of the amount of carbon nanotubes introduced into liposomes on membrane permeability

Abstract

Single-walled carbon nanotubes (SWNTs) have a diameter of several nanometers and can spontaneously insert themselves into lipid membranes, which are the basic component of cell membranes, and allow ions to pass through. Therefore, SWNTs are expected to be incorporated into spherical artificial lipid membranes (liposomes) and used in sensors and drug delivery systems. Currently, ion transport through SWNTs is measured optically using fluorescent probes in nanosized liposomes. However, inserting SWNTs into membranes changes the morphology and mechanical properties of the membranes, and ion influx could occur through defects in the membranes caused by these changes. In this study, we used fluorescence microscopy and giant unilamellar vesicles, which are micrometer-sized liposomes, to observe the state of the liposome membrane and ion transport through the membrane in parallel. To observe ion transport, Ca2+-sensitive fluorescent probes were encapsulated in liposomes, and Ca2+ was added externally. In addition, the amount of SWNTs introduced into the liposome was changed, and the effect of the SWNT concentration on the ion transport was observed. The ion transport through SWNTs was confirmed by the increase in fluorescence intensity. In addition, the ion permeability increased with decreasing SWNT concentration, suggesting that a high SWNT concentration affected the insertion of SWNTs into the membrane.