Sheathless Size-Based Acoustic Particle Separation

Abstract

Particle separation is of great interest in many biological and biomedical applications. Flow-based methods have been used to sort particles and cells. However, the main challenge with flow based particle separation systems is the need for a sheath flow for successful operation. Existence of the sheath liquid dilutes the analyte, necessitates precise flow control between sample and sheath flow, requires a complicated design to create sheath flow and separation efficiency depends on the sheath liquid composition. In this paper, we present a microfluidic platform for sheathless particle separation using standing surface acoustic waves. In this platform, particles are first lined up at the center of the channel without introducing any external sheath flow. The particles are then entered into the second stage where particles are driven towards the off-center pressure nodes for size based separation. The larger particles are exposed to more lateral displacement in the channel due to the acoustic force differences. Consequently, different-size particles are separated into multiple collection outlets. The prominent feature of the present microfluidic platform is that the device does not require the use of the sheath flow for positioning and aligning of particles. Instead, the sheathless flow focusing and separation are integrated within a single microfluidic device and accomplished simultaneously. In this paper, we demonstrated two different particle size-resolution separations; (1) 3 μm and 10 μm and (2) 3 μm and 5 μm. Also, the effects of the input power, the flow rate, and particle concentration on the separation efficiency were investigated. These technologies have potential to impact broadly various areas including the essential microfluidic components for lab-on-a-chip system and integrated biological and biomedical applications.

Vertical Hydrodynamic Focusing and Continuous Acoustofluidic Separation of Particles via Upward Migration

“…Among the single‐layered PDMS‐based devices, similar kind of focusing is not reported before. Due to the utilization of the principal component of ARF, the present device successfully operated for particle separation at net flow rate up to 1.3 mL min −1 , which is ≈100 times higher than used in previously reported SAW devices 20, 23, 31, 32, 37, 38, 42, 43, 47, 48. The throughput of the proposed device can be further improved with ease by increasing the width of the microchannel since the microchannel is placed directly on the IDT.…”

“…The proposed design provided an additional advantage of utilizing both the horizontal and stronger vertical components of the ARF acting on the particles. The height and width of the microchannel did not significantly alter the device performance, unlike the SSAW‐based devices, in which the microchannel aspect ratio significantly affected the locations of the pressure nodes and antinodes 22, 39, 40, 42. The present device utilized a comparatively low input power because the energy loss to PDMS walls was minimal as the IDT was directly exposed to the fluid and both the vertical and horizontal components of the ARF were employed.…”

Particle separation by phase modulated surface acoustic waves

“…The device is built from two identical interdigital transducers (IDTs) with a polydimethylsiloxane (PDMS) microchannel located symmetrically between them. 8,11,44,60,61 The mechanism of particle manipulation based on phase-shifting of an acoustic standing wave is illustrated in Fig. 1b-d.…”

“…43 Increasing the frequency of the field, transducer dimensions and therefore the device size can be reduced and successful sorting can be achieved in microfluidic devices. 11,39,44 The Huang group showed that the efficiency of sorting can be increased by inclining the transducer at a specific angle to the flow direction 9 and the method was applied for the isolation of circulating tumor cells. 45 In recent years, dynamic acoustic approaches, where the time-averaged radiation force changes with time, have gained increasing interest for particle manipulation, and specifically for sorting.…”

Acoustic Manipulation and Alignment of Particles for Applications in Separation, Micro-Templating, and Device Fabrication

“…The pressure is maximum at the antinode and minimum at the node. Due to this pressure differential, solid particles tend to reassemble and concentrate in zones of minimum acoustic potential energy, which is typically at the nodes [14]. In a microchannel multiple nodes could exist depending on the wavelength/frequency of the wave.…”