Increasing The Propulsion Force By Increasing Urease Amount Immobilized On Urease-Powered Janus Spherical Micromotors

Enzyme-powered micro/nanomotors are artificial micro/nanodevices that can be propelled by enzymatic reactions.Because they own the size in micro/nanoscale and can self-propel in aqueous solution,the enzyme-powered micro/nanomotors have great promise for various biomedical applications such as biosensing,active drug delivery and minimally invasive surgery.Currently,the enzymes are used to fabricate enzyme-powered micro/nanomotors including catalase,glucose oxidase,urease and so on.The micro/nanomotors which utilize catalase as catalyst mainly rely on a bubble driving mechanism and thus have a strong driving force.Since they require a high concentration of H₂O₂ as a fuel,they are poor in biocompatibility and are not suitable for use in living organisms.The enzyme-powered micromotors with glucose oxidase and urease as catalysts use glucose and urea components of body fluid as fuel,and have good biocompatibility.However,this kind of enzyme-powered micro/nanomotor mainly relies on self-phoretic mechanism,and the driving force is weak,so it is currently unable to maintain autonomous motion in body fluids.In order to solve this problem,we try to improve the driving force of urease-powered micro/nanomotors by increasing the amount of enzyme.Next,our work will be specified in following two chapters.Firstly,based on the surface roughness of the Janus microparticles combined with the cysteamine coupling technique to increase the coupling site,urease-powered Janus micromotors were prepared.The propulsion force of the motor is increased by increasing the urease content.The number of amino groups on rough surface of the Janus Au/MMP modified with amino group by cysteamine coupling technology was increased by about 21 times.The speed of the motor increases as the urea concentration increases.When the urea concentration reaches 10 mmol/L,the speed of the motor tends to be saturated and can reach 3.75±0.01?m/s and at the same time the prepared motor can move to a specified position according to a predetermined route under the control of an external magnetic field.We present a new method to increase the driving force of urease-powered micro/nanomotors.Moreover,the super-paramagnetic magnetic microspheres in this system can achieve the properties of fast magnetic response,magnetic drive and magnetic control of dispersion and aggregation,which provides the possibility for its application in the field of biomedicine in the human body.Secondly,we proposes a method for further increasing the driving force of the enzyme-powered micro/nanomotor by using protein self-assembly technology to realize the spatial expansion of the enzyme to increase the amount of enzyme on the motors.Combining biotin/urease onto Biotin/Au/MMP Janus particles by specific binding of streptavidin and biotin,we can obtain multilayer urease-powered Janus micromotors.The speed of the prepared motor was significantly improved to 21.49±0.62?m/s at the urea concentration of 10 mmol/L,which was 2–3 times higher than the previously reported urease-powered micro/nanomotors.The speed of urease-powered Janus micromotors modified with multilayer Biotin/ureases were regulated by adjusting protein assembly conditions.There are three points about optimal protein assembly conditions.The first one,the concentration ratio of streptavidin to Biotin/urease is 1:3.The second one,Biotin/urease has an initial mass of 60?g.The last one,reaction time is 12 h.The speed of the motor increases with the increasing of urease amount.When urease amount increases to a certain extent,the speed of the motor will not increase.The prepared motor can move to a specified position according to a predetermined route under the control of an external magnetic field.At the same time,Janus urease-powered micromotors modified with multilayer of Biotin/ureases can move in a simulated blood viscosity solution?10 mmol/L urea,35 w/v%sucrose?,and the speed of the motors can reach to 1.89?m/s.We propose a method to increase the driving force of Janus urease-powered magnetic micromotors by increasing the three-dimensional active site,and promote the enzyme-powered micro/nanomotor in the field of biomedicine.