Applied Basic Research On Opto-thermal Micromotor

The development of micro-nano processing technique has bloomed the research on micro/nano-micromotors(MNM).The application of MNM includes environmental remediation,micro/nano self-assemblies,non-invasive surgery,etc.The energy to drive these MNM are originated from chemical reaction,heat field,magnetic field,light,etc.,among which the light-driven,especially the MNM propelled by photothermal effect and thermophoretic force is thought to be a non-contact,fuel-free and biocompatible alternative to application.This dissertation aims to theoretically and experimentally clarify and speculate the motion of a microparticle made exclusively from polystyrene(PS)with its surface covered by gold nanoparticles(AuNP),or the PS@Au opto-thermal micromotor(OTM)and to explore its possible application in motile SERS detection.The partial equations depicting phoretic force and phoretic velocity of the opto-thermal micromotor in liquid were derived in equations before turning to numerical calculation.FEM simulation was performed by means of COMSOL 5.4,in which a series of critical parameters were configured,including two types of two-dimensional component geometry,the lateral and vertical 2D geometry,the material nodes and such physical interfaces as heat transfer,solid mechanism and creeping flow(or stokes flow).Fluid structure interaction(FSI)and non-isothermal flow(NITF)were introduced as multiphysics interfaces in order to couple the physical all physical modules mentioned above.With accurate setting of moving mesh and mesh building,Time-dependent study on OTM motion within hundreds of milliseconds was realized.The fluid fields simulated by lateral and vertical 2D model were compared.Considering of effect of glass slide thin layer,2D vertical model is more complex and has more lengthy calculation to uncover the motion details of OTM from bottom to a certain height.Excluding the thin glass layer at the bottom,2D lateral model is much simpler and more robust when calculating the correlation between laser power and average velocity of OTM.The execution of numerical simulation is to understand tumble motion mechanism of OTM and to optimize its structural design as well as laser-driven experiment and application.The optical path for laser-propulsion experiments of OTM,the point-spot-focused and line-spot-focused optical path are designed,optimized and evaluated by ZEMAX.The focus quality and imaging quality are discussed between the two type of optical path.Chapter 4 illustrates the laser-driven experiments and application study of OTM.In terms of the velocity,the locomotion of the OTM is classified into explosive ejection and slow tumble,with immobile spot applied for the former and motile spot used for the latter.By applying a tightly focused TEM₀₀ spot with power ranging from 4-8 mA on OTM,the average speed of ejective motion of OTM indicates a linear relationship with the laser power.Through microscope equipped by high-speed camera at 20,000 frames per second,the motion traces measured using Image J animal tracker plugin shows a velocity of 0.8m/s.Further,under laser spot power of 10 mW and at frame rate of 100,000,the generation of a hot bubble,or a phase transition surrounding the OTM owing to laser-induced accumulated heat on OTM surface against the direction of motion was captured at the initial moment of ejection.Nearly uniform linear motion was proved in the initial time period of 40?s by comparing to the formula calculation.On the other hand,the tumble motion is realized by limiting the OTM within micro-channels.The analysis of ordinary video frames shows that OTM can be robustly and linearly driven with laser spot power as low as 6 mW.As a prospect for application,the spherical surface of the OTM was successfully applied as a substrate for the detection of surface enhanced Raman spectrum(SERS)of 4-Mercaptobenzoic acid(4-MBA)molecules absorbed onto the OTM surface,in which a Raman spectral detection module was appropriately coupled with the laser-driven optical system above.