Formation Mechanism Of EggPC Vesicles On Carbon Fiber Electrode

Giant unilamellar vesicles (GUVs) of10-100m can be obtained by electroformation method. Similar size and bilayer structure to that of bio-membrane, vesicles can be widely used as the model of cell membrane and drug carrier. This paper broke through the restrictions of conventional electrode and introduced the microelectrode of carbon fbers into the research of vesicle electroformation for the first time. Because of its small size, the microelectrode of carbon fbers has excellent electrochemical properties, which makes many potential applications of vesicles into full play. This paper elaborated the electroformation of vesicles on the microelectrode of carbon fbers in the following three aspects.Firstly, this paper revealed the formation mechanism of egg phosphatidylcholine (EggPC) vesicles on carbon fiber electrode. Under the electric field, electric double-layer formed between the interface of the carbon fiber electrode and the electrolyte, which caused directional movement of the EggPC molecules and accumulated around the carbon fibers. So the formation of GVs focused on the carbon fiber electrode. Then the electrostatic repulsion arises between the electrode and lipid bilayers under the alternative current (AC) electric field. Both of the electrostatic repulsion and a weak mechanical vibration may be the basic driving forces for the lipid bilayers separation each other and bending to form GVs. Hence, in addition to the previously reported electro-osmotic flow, electro-adsorption should share the fundamental part of the mechanism for the electroformation of vesicles.What’s more, giant vesicles were obtained over a wide frequency range of1-3000Hz and peak-to-peak value from0.212V/mm to20V/mm between two parallel conducting electrodes of carbon fibers under AC electric field. The influence of AC voltage and frequency on the structural evolution of giant vesicles was in situ observed by inverted optical microscope. With the increase of frequency, the number of vesicles gradually decreases. When the frequency is greater than1000Hz under the constant voltage of1.5V, the rate of the vesicle formation decreases. It is found that the best potential parameter of the vesicle formation is5V at the frequency of20Hz. When the potential is too high or too low, the formation of the vesicles is not ideal. In the end, we explored the retention time of vesicles in distilled water under four kinds of representative AC electric field parameters with different energizing time. It was found that it was not beneficial to the preservation of vesicles if the energizing time was too long or short, and the optimal time was1h. In order to simulate the buffer system in the blood, we also introduced the phosphate buffer solution, which greatly extended the preservation time and the highest critical concentration of vesicle formation. Based on the in situ observation by an inverted microscope, the disappearing mechanism of vesicles was presented.