| By merging acoustic waves with microfluidics,acoustofluidics has been developed to be a professional field that is attracting people’s interest.However,ultrahigh frequency acoustofluidics has rarely studied due to the lack of such a high frequency acoustic device.Up to now,the acosutofluidics focus on utilization of acoustic waves with frequency from kilohertz(i.e.ultrasound)to several megahertz.In this work,gigahertz film bulk acoustic wave resonator was integrated in a microfluidic system,to explore the phenomenon and applications of ultrahigh frequency acoustofluidics for the first time.Triggered by the gigahertz acoustics,a three-dimensional micro-vortex array was generated in the microfluid,breaking through the limitation of scale effect of acoustic streaminging.This work focuses on the principles of acoustofluidic vortex generation and tuning,based on which the acosutofluidic technology has been successfully developed for some significant applications including microfluidic mixing,micro/nanoscale tweezering,and nanoscale biosensing.This work contributes to a better understand of ultrahigh frequency acoustofluidics,and also enables a wide range of acoustofluidic-based fundamental applications.Reveal the physical principles of the generation of the micro-vortex array with theoretical analysis,simulation,and experiments.Especially,the role of gigahertz frequency has been figured out in details,demonstrating a body force dominated acoustofluidic technology.The formation of the vortex velocity field was characterized with finite-elment simulation and particle experiments.By tuning the size of microchannel or resonator,the generation of the vortex array(ten individual vortices formed around the pentagon resonator)has been clearly presented and explained.These fundamental theories and principles form the basis of the understanding,as well as the development of gigahertz acoustofluidics.Acoustic streaming provides many interesting stetegies for microfluids and micro/nanoscale objects manipualtions.Localized acoustic streaming,especially generation of micro-vortex has been long term explored to reshape the microfluidic stream for high efficiency and multifunctional operations of fluids and suspensions.In this chaptert,we further study its tunable properties of the acoustofluidic vortex to reveal the ability of reshaping and mixing micron-and nano-scale flows.Ultrafast mixing within 400 microsenconds with 91% mixing efficiency at 60 μL/min(corresponding to an average velocity of 3.33 cm/s)has been realized.Particularly,the vortex can be effectively triggred in a wide frequency band,showing its robust performance for microfluidic mixing related applications.Developing microrobots for precise manipulations of micro/nanoscale objects has triggered tremendous research interests for applications in biology,chemistry,physics and engineering.Here,we present a novel hypersonic induced hydrodynamic tweezers(HSHTs),which use a gigahertz nano-electromechanical resonator to create localized 3D vortex stream array for the capture and manipulation of micro-and nanoparticles in three orientations: transportation in a plane and self-rotation in place.3D vortex stream can effectively pick up particles from the flow,whereas the highspeed rotating vortices are used to drive self-rotation simultaneously.By tuning flow rate,the captured particles can be delivered,queued and selectively sorted through the 3D HSHTs.We demonstrate,through numerical simulations and theoretical analysis,the generation of the 3D vortex and the mechanism of the particle manipulations by ultrahigh frequency acoustic wave.Benefiting from the advantages of acoustic and hydrodynamic method,the developed HSHTs work in a precise,non-invasive,label-free,and contact-free manner,enabling wide applications in micro/nanoscale manipulations and biomedical researches.An Acousto Fluidic Trap(AFT)biosensor is demonstrated by introducing and manipulating nanoparticles into the gigahertz acoustic wave actuated microfluidic system.First of all,an AFT consisting of ten independent standing vortices was generated,and was further demonstrated with excellent kinetics for effective capture and enrichment of nanoparticles as small as sub-100 nm.Benefit from the closed formation and high-speed rotation of the vortices,the AFT works stably both in flowing and static fluids.We investigated two biosensing modes using specific bound nanoparticles(SBNPs).The Nano-Filter approach gives a quick but accurately molecular quantification;the offline incubation approach is suitable for low concentration detection due to molecular enrichment with response enhancements of ～100 times.Additionally,we the theoretically and experimentally studied optimizations of AFT in samples of different volume and flowing rate,revealing a wide use of AFT for different biosensing cases. |
