Study On Enhanced Diffusion Of Dendritic Silica GO_x-Pt Catalyzed Nanomotors

The micro/nanomotors can convert the energy in the surrounding environment(such as chemical energy,magnetic field,light energy,acoustic energy,electrical energy,etc)into mechanical kinetic energy,which can realize the loading,transportation and release of various micro/nanocargoes in liquid media.The fields of medicine,environmental governance and micro/nano processing have important application prospects.Enzyme-driven micro/nanomachines have become an important part of biomedical micro/nanomotors due to their excellent biocompatibility,sustainability,and the diversity of enzyme-"fuel"combinations.The micro/nanomotors driven by glucose oxidase(GOx),urease,or catalase are currently the main enzyme-driven motors.Compared with micro/nanomotors driven by urease or catalase,GOx-catalyzed micro/nanomotors can use glucose,widely present in the organism and whose concentration can be adjusted,as a"fuel",which has significant advantages in the application of biomedicine.Since H₂O₂ with a certain degree of biotoxicity will be produced during GOx catalytic reaction,micro/nanomotors using glucose as the"fuel"are mostly driven by the dual enzymes of GOx and catalase(Cat).Although this design consumes H₂O₂ in the reaction process,the Cat loading will undoubtedly occupy some of the active sites of GOx and reduce the reaction activity,due to the competition of enzyme coupling site between GOx and Cat on the surface of the motor.On the other hand,currently dual-enzyme-powered motors are mostly concentrated on the micron size,which limits its application in biomedicine.Therefore,in this paper,in view of the problems of weak driving force and excessive motor size of glucose-fueled micro/nanomotors,a dendritic mesoporous silica nanosphere with a larger pore size was selected as the carrier through the design of the motor structure.The cascade reaction of spatially separated GOx-Pt provides the driving force for efficient driving of nanomotors.First,mesoporous silica nanospheres(MSNs)with enlarged pore size have been prepared by oil-water biphasic synthesis using cetyltrimethylammonium salts(CTAC)or cetyltrimethylammonium bromide(CTAB)as templates and cyclohexane as oil phase reagents.Large-pore mesoporous silica nanospheres with a particle diameter of50?100 nm and an average pore diameter of 6?10 nm were prepared,and their morphology and structure were characterized.At the same time,the prepared MSNs were cross-linked by glutaraldehyde for the fixation of GOx(GOx@MSNs).The effects of surfactants on the physical and chemical properties of the MSNs,and the pore size and channel structure of the carrier on the amount of immobilized enzyme were systematically investigated.The results show that the larger pore size and the better connectivity are in favor of enzyme immobilization.The amount of enzymes immobilized on MSNs reaches 230.4 mg/g that is three times higher than that on the well-known mesoporous SBA-15.Simultaneously,the enzyme activity has no significant loss after immobilization.Second,the nanomotor with glucose as a"fuel"was constructed by using dendritic mesoporous silica nanospheres as carriers,loaded with GOx and Pt nanoparticles(Pt NPs).Transmission electron microscopy,X-ray energy spectroscopy analysis,and infrared spectroscopy were used to characterize the structure and morphology of the nanomotor.The effects of glucose concentration,nanomotors structure and the amount of GOx and Pt NPs on the enhanced diffusion behavior of nanomotors were also investigated.And we analyzed the reason of speed increasing of GOx-Pt nanomotors.The results show that the particle size of dendritic mesoporous silica is 90-100 nm with a pore diameter of 6.05 nm.Pt NPs were mostly fixed in the mesoporous channels.The nanomotor obtained a relatively high speed about 4.42±1.4?m/s(38 body length/s)in 200 mmol/L glucose aqueous solution.As the amount of amino modification increases,the number of immobilized GOx increases.The GOx-Pt cascade reaction promotes the oxidative of glucose,expands the concentration gradient,and enhances the diffusion of cascade-reaction GOx-Pt nanomotors.These all provide the possibility for glucose-fueled dendritic silica GOx-Pt catalyzed nanomotors to enter more organs or tissues with higher driving force in further biomedical applications.