title: Continuous micro-vortex-based nanoparticle manipulation via focused surface acoustic waves.
abstract: Despite increasing demand in the manipulation of nanoscale objects for next generation biological and industrial processes, there is a lack of methods for reliable separation, concentration and purification of nanoscale objects. Acoustic methods have proven their utility in contactless manipulation of microscale objects mainly relying on the acoustic radiation effect, though the influence of acoustic streaming has typically prevented manipulation at smaller length scales. In this work, however, we explicitly take advantage of the strong acoustic streaming in the vicinity of a highly focused, high frequency surface acoustic wave (SAW) beam emanating from a series of focused 6 μm substrate wavelength interdigital transducers patterned on a piezoelectric lithium niobate substrate and actuated with a 633 MHz sinusoidal signal. This streaming field serves to focus fluid streamlines such that incoming particles interact with the acoustic field similarly regardless of their initial starting positions, and results in particle displacements that would not be possible with a travelling acoustic wave force alone. This streaming-induced manipulation of nanoscale particles is maximized with the formation of micro-vortices that extend the width of the microfluidic channel even with the imposition of a lateral flow, occurring when the streaming-induced flow velocities are an order of magnitude larger than the lateral one. We make use of this acoustic streaming to demonstrate the continuous and differential focusing of 100 nm, 300 nm and 500 nm particles.
authors.affiliation: Pillar of Engineering Product Development, Singapore University of Technology and Design, Singapore 487372, Singapore. aiye@sutd.edu.sg and Singapore-MIT Alliance for Research and Technology (SMART) Centre, Singapore 138602, Singapore.
authors.forename: David J
authors.initials: DJ
authors.lastname: Collins
authors.affiliation: Pillar of Engineering Product Development, Singapore University of Technology and Design, Singapore 487372, Singapore. aiye@sutd.edu.sg.
authors.forename: Zhichao
authors.initials: Z
authors.lastname: Ma
authors.affiliation: Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA and Singapore-MIT Alliance for Research and Technology (SMART) Centre, Singapore 138602, Singapore and Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Jongyoon
authors.initials: J
authors.lastname: Han
authors.affiliation: Pillar of Engineering Product Development, Singapore University of Technology and Design, Singapore 487372, Singapore. aiye@sutd.edu.sg.
authors.forename: Ye
authors.identifier: 0000-0001-8638-1649
authors.initials: Y
authors.lastname: Ai
mesh_terms: D057446:Hydrodynamics; D056656:Lab-On-A-Chip Devices; D053758:Nanoparticles / Q000737:chemistry*; D009556:Niobium / Q000737:chemistry; D010087:Oxides / Q000737:chemistry; D010316:Particle Size; D013016:Sound
chemical_list: D010087:Oxides; D009556:Niobium; C091692:lithium niobate