Enzymatic Janus Liposome Micromotors

Abstract

A liposome-based micromotor system\nthat utilizes regional enzymatic\nconversion and gas generation to achieve directional motion in water\nis presented. Constituted mainly of a low-melting lipid and a high-melting\nlipid together with cholesterol, these liposomes maintain stable Janus\nconfiguration at room temperature as a result of lipid liquid–liquid\nphase separation. Local placement of enzymes such as horseradish peroxidase\nis realized via affinity binding between avidin and biotin, the latter\nas a lipid conjugate sorted specifically into one domain of these\nJanus liposomes as a minor component. In the presence of the substrate,\nhydrogen peroxide, these enzyme-decorated Janus liposomes undergo\ndirectional motion, yielding velocities exceeding thermal diffusion\nby three folds in some cases. Experimental details on liposome size\ncontrol, motor assembly, and substrate distribution are presented;\neffects of key experimental factors on liposome motion, such as substrate\nconcentration and liposome Janus ratio, are also examined. This work\nthus provides a viable approach to building asymmetrical lipid-assembled,\nenzyme-attached colloids and, in addition, stresses the importance\nof asymmetry in achieving particle directional motion.