Quantification of C60-induced membrane disruption using a quartz crystal microbalance

Direct contact between fullerene C-60 nanoparticles (NPs) and cell membranes is one of mechanisms for its cytotoxicity. In this study, the influence of C-60 NPs on lipid membranes was investigated. Giant unilamellar vesicles (GUVs) were used as model cell membranes to observe the membrane disruption after C-60 exposure. C-60 NPs disrupted the positively charged GUVs but not the negatively charged vesicles, confirming the role of electrostatic forces. To quantify the C-60 adhesion on membrane and the induced membrane disruption, a supported lipid bilayer (SLB) and a layer of small unilamellar vesicles (SUVs) were used to cover the sensor of a quartz crystal microbalance (QCM). The mass change on the SLB (Delta m(SLB)) was caused by the C-60 adhesion on the membrane, while the mass change on the SUV layer (Delta m(SUV)) was the combined result of C-60 adhesion (mass increase) and SUV disruption (mass loss). The surface area of SLB (A(SLB)) was much smaller than the surface area of SUV (A(SUV)), but Delta m(SLB) was larger than Delta m(SUV) after C-60 deposition, indicating that C-60 NPs caused remarkable membrane disruption. Therefore a new method was built to quantify the degree of NP-induced membrane disruption using the values of Delta m(SUV)/Delta m(SLB) and A(SUV)/A(SLB). In this way, C-60 can be compared with other types of NPs to know which one causes more serious membrane disruption. In addition, C-60 NPs caused negligible change in the membrane phase, indicating that membrane gelation was not the mechanism of cytotoxicity for C-60 NPs. This study provides important information to predict the environmental hazard presented by fullerene NPs and to evaluate the degree of membrane damage caused by different NPs.