Abstract
Acoustofluidic devices for manipulating microparticles in fluids are
appealing for biological sample processing due to their gentle and
high-speed capability of sorting cell-scale objects. Such devices are
generally limited to moving particles toward locations at integer
fractions of the fluid channel width (1/2, 1/4, 1/6, etc.). In this
work, we introduce a unique approach to acoustophoretic device design
that overcomes this constraint, allowing us to design the particle
focusing location anywhere within the microchannel. This is achieved by
fabricating a second fluid channel in parallel with the sample channel,
separated from it by a thin silicon wall. The fluids in both channels
participate to create the ultrasound resonance, while only one channel
processes the sample, thus de-coupling the fluidic and acoustic
boundaries. The wall placement and the relative widths of the adjacent
channels define the particle focusing location. We investigate the
operating characteristics of a range of these devices to determine the
configurations that enable effective particle focusing and separation.
The results show that a sufficiently thin wall negligibly affects
focusing efficiency and location compared to a single channel without a
wall, validating the success of this design approach without
compromising separation performance. Using these principles to design
and fabricate an optimized device configuration, we demonstrate
high-efficiency focusing of microspheres, as well as separation of
cell-free viruses from mammalian cells. These “transparent wall”
acoustic devices are capable of over 90% extraction efficiency with 10
mm microspheres at 450 mu L min(-1), and of separating cells (98%
purity), from viral particles (70% purity) at 100 mu L min(-1).