Research On Particle Enrichment And Separation Based On Surface Acoustic Wave (SAW)

With the rapid development of biochemical analysis,disease diagnosis,and precision medicine,people are demanding higher precision for rapid analysis of biochemical samples,separation and detection of cells,targeted treatment of drugs and precision drug administration.Surface acoustic wave(SAW)-based devices have the advantages of real-time,label-free detection capability,remote control function and simple operation.The acoustic radiation force(ARF)generated by the acoustic surface waves can precisely manipulate and capture particles or cells suspended in liquids,offering great potential for applications.In most test cases,sample detection requires only a drop or less,and if samples of tiny objects(cells or particles)can be captured and enriched quickly and inexpensively,the amount of fluid handled can be significantly reduced,greatly improving the sensitivity and accuracy of sample analysis and detection.However,when the sample volume increases and the composition is complex,it is difficult to achieve selective capture and enrichment with conventional methods,such as the isolation of circulating tumor cells(CTCs)from blood.Therefore,for cell samples within complex systems,further dynamic separation and collection of samples is required.As a prerequisite for downstream analysis and diagnosis,obtaining highly purified intact active cells from complex environments has always been a challenge.Based on the above problems,this thesis proposes to study the precise manipulation and separation of the novel acoustic tweezer particle manipulation technique at the micro-nano scale.Explore the near-field acoustic-fluid-solid coupling attenuation and particle isotropic scattering law,dissect the distribution and strength of the acoustic field and sound pressure,clarify the acoustic-electric coupling mechanism of lithium niobate single crystal and acoustic-fluid-solid coupling law;further match the multi-mode application environment,tune the acoustic field strength and acoustic field region,and realize the precise acoustic field modulation technique.Finally,a specially designed tunable acoustic tweezer chip is used to realize the effective enrichment and separation of objects in strong gradient acoustic fields.It provides an effective solution for the highly sensitive and rapid enrichment and detection of trace samples,early diagnosis of cancer and therapeutic practice.The main research contents are as follows.Rapid capture and enrichment of samples.Firstly,the acoustic flow effect and acoustic radiation mechanism of acoustic surface waves under microscopic fluids were analyzed and studied,and simple operations such as moving,merging and mixing of microdroplets on lithium niobate substrate were realized with the help of acoustic wave propagation law and particle control principle;further,a miniaturized acoustic fast capture and enrichment chip with simple operation was designed to capture microdroplets in sessile droplets using three frequencies(99.1,48.8,20.4 MHz)based on traveling surface acoustic wave(TSAW),48.8,20.4 MHz)devices to trap suspended polystyrene(PS)microspheres of different sizes(5,20,40 μm)in sessile droplets that are aggregated into particle clusters or rings under the control of acoustic field-induced fluid vortex(acoustic vortex).Further modulation of the acoustic field enables free switching of the "cluster-ring" and free control of the ring diameter,which provides the possibility of diluting or concentrating the particles to a specific concentration.This provides a powerful tool for enhanced microfluidic detection and chemical analysis by effectively achieving enhanced regulation of particle concentration,especially for micro sample concentration.Based on the previous study,a technique based on ultra-narrow-band surface traveling waves was designed for the precise separation of live cells.By comparing three different structures of forked-finger transducers,a structurally well-designed and optimized slant-finger transducer(S-IDT)was finally selected to achieve a freely tunable SAW operating frequency that can excite a narrow-band beam with higher energy density.In this study,the device performance was optimized using PS particles of different sizes and blood cells spiked with cancer cells(MCF-7,human breast cancer cells).Precise separation of 10 μm out of 5,10 and20 μm particles and 8 μm and 10 μm particles was achieved.The optimal frequency for 10 μm separation of intermediate particles in multiple mixtures was determined by theory and testing,and then the sensitivity of the three particles to changes in acoustic amplitude was tested by varying different input voltages.The effects of flow rate and voltage variations on the separation performance of intermediate particle size were further tested separately to derive the optimal separation conditions for the equipment.Finally,the separation efficiency and purity of 10 μm particles reached 98.75% and 98.10%(optimum separation performance),respectively.In addition,the isolation of CTCs from blood cell samples spiked with MCF-7was investigated,and the cell purity,cell recovery and cell viability after sorting operation were tested by live/dead cell double staining and ICC cell immuno-antibody labeling method,and the final separation efficiency reached over 98% and purity reached 93%.Finally,the isolated cancer cells were cultured for 24,48 and 72 hours with activity higher than 97% and good proliferation ability,further demonstrating that the device can isolate live cells without damage.