Study On The Design,Motion And Properties Of Fuel-free Micro/Nanomotors And Cilia Arrays

Micro/nanomotors or machines(MNMs)are micro or nanosized devices that can convert the energy from environment into their autonomous motion.According to the propulsion mechanisms,MNMs can be classified into chemically-powered MNMs and external field propelled MNMs.They have shown attractive applications in environmental remediation,cargo/drug delivery,cells separation,biosensing and microengineering.The so far most developed MNMs rely on toxic fuels and surfactants,which lead to the secondary pollution in environment and also the unstable motion and limited lifetime of MNMs with the consumption of fuels.It will severely impede their real applications.The fuel-free MNMs can continuously obtain the fuels in running solutions or are no fuels required.Accordingly,the stable movement of MNMs can be maintained in long time and the compatibility with environment and living body will be highly improved,which will accelerate the implementation of the real applications of MNMs in environment and biomedicine.This thesis develops the fuel-free TiO₂/Pt Janus micromotors,magnetic photonic nanochains cilia arrays and Mg/Pt Janus micromotors respectively by taking advantages of photocatalytic water splitting reaction,active metal-water reaction and fuel-free external field propulsion mechanism.We study their light-controlled motion and magnetic actuation in aqueous solution,and also the cytotoxicity of the motion in biological fluid.Meanwhile,the applications of the developed MNMs in pollutants degradation,fluid or cargoes transportation,sensing and detection have been demonstrated.The light-controlled motion of pure water-fuelled TiO₂/Pt Janus MNMs is developed.The motion of TiO₂/Pt Janus micromotors is governed by light-induced self-electrophoresis under the local electrical field generated by the asymmetrical redox reactions and the concentration gradient of protons on two sides.TiO₂ side and Pt side are oppositely charged due to the separation of photogenerated electrons and holes.Herein,we can reversibly manipulate the aggregation and separation of TiO₂/Pt Janus micromotors by using pulsed UV irradiation.Subsequently,the chemotactic motion of TiO₂/Pt Janus micromotors is illustrated by regulating the distribution of ionic products with different UV intensities,which make some TiO₂/Pt Janus micromotors return to home position along the initial path after turn off the UV light.Meanwhile,we demonstrate that the photocatalytic degradation efficiency of Rhodamine B(Rh B)and 2,4-dinitrotoluene(DNT)can be improved by using TiO₂/Pt Janus micromotors under UV illumination due to the enhanced mass transfer in solution and active adsorption of molecules by the fast motion of micromotors.To overcome the limited running scale of micromotors,we propose the concept of“aircraft carrier”by transporting and releasing TiO₂/Pt Janus micromotors with a millimeter-scale tubular motor for enhanced large-volume degradation of 2,4,6-trinitrophenol(TNP).The tubular millimotor can move fast through Marangoni effect induced by asymmetrically releasing ethanol from the end of motor.Meanwhile,TiO₂/Pt Janus micromotors can be released and uniformly dispersed in solution for“on-the-fly”degradation.Moreover,a wall-following motion of the tubular motor is generated by the chemiosmotic flow at the wall vicinity due to the diffusion-obstacle effect.As such,the tubular motor can be autonomously navigated by topographical pathways without the guidance of external fields which shows the potential application as an intelligent robot.The magnetically actuated artificial cilia arrays are external filed propelled micromachines which can cause the directional fluid flow and mixing by their in-situ rotation.They have advantages of highly-controlled motion,no fuels required and excellent environment compatibility.We develop the printing method for one-step fabrication of self-adaptive magnetic photonic nanochain cilia arrays on the amino-groups modified substrate,which are capable of achieving in-situ visual p H detection and self-adaptive fluid pumping due to the real-time adjustable interparticle distance and total length in response of the volume change of the hydrogel shell with the p H value of the pumped fluids.Benifitted from the integrated functions of environmental sensing and self-adaptive fluid pumping,the cilia arrays developed here promise a significant advance in intelligent biomimetic microdevices and microfluidic systems.Comparing with the aforementioned light-controlled micromotors and magnetically actuated cilia arrays in aqueous solution with low viscosity,the bubble-propelled Mg-based micromotors can overcome the high viscosity of body fluid which exhibit the potential applications in vivo.We perform the in vitro cytotoxicity study of Mg/Pt Janus micromotors with different human cell lines,which show a low cytotoxicity with an appropriate concentration.Then,we present the improvement of the electrochemical detection of glucose by the accelerated redox reactions on electrode owing to the enhanced mass transfer in human serum by the fast motion of Mg/Pt Janus micromotors.In addition,we synthesize the mesoporous SiO₂ coated Mg core-shell partilces to restrain the bubble generation because the bubbles produced by Mg-based micromotors are biohazardous.The introduction of mesoporous shell will decrease the Mg-water reation rate and make most generated hydrogen dissolved in solution.Furthermore,we illustrate that the as-obtained partilces can be acted as H₂ drugs to protect the cells from oxidative damage by scavenging the continuously produced hydroxyl radicals,which lay the foundation for the development of bubble-free biocompatible Mg-based micromotors.