Construction And Application Of Rare Earth Upconversion Micro/Nano Motors

Micro/nanomotors are a class of micro-machines that can convert chemical energy or other forms of energy into their own driving force and obtain autonomous motion.Its autonomous movement capability has great application potential in the fields of environmental governance,biological detection and sensing,and targeted drug delivery.However,the preparation process of most micro/nanomotors is complicated for surface modification,and their biocompatibility is weak,which hinders their development in practical applications.In recent years,upconversion micro/nano materials based on sodium tetrafluoroyttrium（Na REF₄,RE:rare earth element）have excellent properties such as long fluorescence lifetime,deep tissue penetration ability,stable chemical and physical properties,and no damage to biological tissue.Its performance has attracted widespread attention,in particular,it has great application value in environmental monitoring,biosensing,drug treatment and so on.However,problems such as surface defects and low energy transfer efficiency limit the application development of upconversion materials.Therefore,it is of great significance to develop new strategies for improving the luminescent efficiency and sensitivity of rare-earth upconversion luminescent materials.Converting upconversion luminescent materials into biocompatible micro/nanomotors capable of autonomous motion can overcome the limitation of passive diffusion and enhance the interaction between reactants through the active motion capability of motors,which is expected to enhance the luminescence function of upconversion materials and provides new ideas for the development of micro/nanomotors.Based on this,this paper takes Na YF₄-based upconversion light-emitting materials as the research object,and combines different driving methods to construct several different upconversion light-emitting micro-nanomotors,and the following researches are carried out around their design,synthesis,motion behavior,and potential applications:First,the Janus polyelectrolyte microcapsule motor with surface-modified Na YF₄:Yb³⁺,Er³⁺upconversion nanoparticles（UCNPs）and metal platinum（Pt）with catalytic properties was designed and fabricated by layer-by-layer self-assembly technology.The structure and morphology of UCNPs and microcapsule motors were investigated by means of transmission electron microscopy,scanning electron microscopy and fluorescence microscopy.The results indicate that the UCNPs and the microcapsule motor have uniform and stable morphologies and good monodispersity,and the microcapsule motor has hollow and asymmetric structure.The motion of the microcapsule motor in the hydrogen peroxide solution was explored,and it was found that the motor speed increased with the increase of the hydrogen peroxide concentration,in 10%hydrogen peroxide solution,the velocity can be as high as 110μm/s,and it shows a periodic change with the generation and diffusion of oxygen bubbles.The constructed microcapsule motor was applied to the detection of trinitrotoluene（TNT）to explore its potential application in micro/nano sensors.Because the energy transfer between the surface-modified 3-aminopropyltriethoxysilane（APTES）of the UCNPs and TNT,TNT can quench the fluorescence of UCNPs,proving that the microencapsulated motor has the ability to rapidly detect harmful substances.Fluorescence microscopy experiments and fluorescence spectra analysis displayed that the concentration of TNT was proportional to the fluorescence change of UCNPs,the detection limit of TNT was 2.4 ng/m L,and the detection efficiency was increased by about 3.5 times compared with non-motor UCNPs,and the detection efficiency is proportional to the hydrogen peroxide concentration.Then,in view of the poor biocompatibility and biotoxicity of hydrogen peroxide as a fuel for micro/nano motors,Na YF₄:Yb³⁺,Tm³⁺upconversion nanoparticles,uricase and horseradish peroxidase（HRP）were modified on the surface of silica microspheres by semi-embedding method to prepare Janus micromotors driven by enzyme-catalyzed reaction.Scanning electron microscope,laser confocal microscope,X-ray diffraction and other characterization results show that the synthesized UCNPs are pure hexagonal phase with good monodispersity.The two sides of the prepared micromotor were successfully modified with UCNPs and biological enzymes respectively,forming the Janus asymmetry structure.The movement behavior of the motor under different uric acid concentrations was researched,and it was found that the movement speed of the motor increased with the increase of the uric acid concentration.When the uric acid concentration was 5 m M,the movement speed of the motor could reach 6.8μm/s,and the diffusion coefficient was 1.83μm/s².At the same time,the ability of UCNPs fluorescence to detect uric acid was used to further explore the application potential of this motor in biosensors.Uricase can oxidize uric acid to generate hydrogen peroxide,and hydrogen peroxide oxidizes o-phenylenediamine（OPD）under the catalysis of HRP to generate ox OPD,which can quench the fluorescence of UCNPs.The results of fluorescence spectroscopy and other analysis revealed that the concentration of uric acid was proportional to the change of the fluorescence intensity of UCNPs.The detection limit of uric acid was 1.59μM.Compared with non-motor,the detection efficiency was increased by 3.39 times,and the detection of uric acid in simulated urine was realized.More importantly,this method uses the detection object as fuel to drive the motor for autonomous movement without additional power or energy,which provides a new idea for the design of biosensors and micro/nano motors.Subsequently,a Janus upconversion nanoparticle motor was designed and prepared by asymmetric modification of urease on the surface of silica-coated Na YF₄:Yb³⁺,Er³⁺upconversion nanoparticles by semi-embedding method.The morphology and structure of UCNPs were analyzed by transmission electron microscope,scanning electron microscope and other means.The results exhibited that the size of UCNPs coated with silica was about 100 nm with good monodispersity and stable structure,and urease was successfully modified on one side of the particle,showing an asymmetric structure.It is found that the motor speed increases with the increase of urea concentration.When urea concentration is 50 m M,the motor speed can reach 18.2μm/s,and the diffusion coefficient is 12.1μm/s².More importantly,positive chemotaxis of the nanomotor were observed under urea concentration gradient,and this chemotaxis can be used for active drug delivery or active targeted therapy.Finally,based on the research on chemically driven rare earth upconversion micro/nano motors,a physically driven rare earth upconversion micro motor was constructed.micron-sized Na YF₄:Yb³⁺,Er³⁺upconversion particles were synthesized by hydrothermal method,and a photothermally driven gold-shell half-coated Janus UCNPs motor was fabricated by vacuum sputtering coating method.This photothermal drive-based motor can realize the process of converting light energy into thermal energy and then into mechanical energy for autonomous movement.The morphology and structure were analyzed by means of scanning electron microscopy,dynamic light scattering,X-ray diffraction,etc.The results confirmed that the size of the prepared upconversion particles was between 0.8-1.2μm,the monodisperse type was good,and the structure was stable.The gold shell by vacuum sputtering was successfully decorated on one side of the upconversion particles,forming an asymmetric structure.The motion behavior of the motor driven by different power lasers was further studied,and it was found that the motor speed increased with the increase of the laser intensity.Under the laser power of 1.0 W/cm²,the motor speed could reach 21μm/s.The application of near-infrared light-driven motors in sensors is investigated.A high-efficiency and high-sensitivity fluoride ion microsensor is constructed by utilizing the fluorescence quenching effect between fluoride ions and upconversion particles.In the presence of curcumin,the absorption peak of fluoride ions overlapped with the emission peak of the upconverting particles,thereby quenching the fluorescence of the upconverting particles.The analysis results of fluorescence and UV spectra indicated that the concentration of fluoride ions was proportional to the fluorescence change of the upconversion particles,the detection limit of fluoride ions was 2.62μM,and the detection efficiency was proportional to the laser power.