A pumpless acoustofluidic platform for size ... - ACS Publications

Subscriber access provided by READING UNIV

Article

A pumpless acoustofluidic platform for size-selective concentration and separation of microparticles Husnain Ahmed, Ghulam Destgeer, Jinsoo Park, Jin Ho Jung, Raheel Ahmad, Kwangseok Park, and Hyung Jin Sung Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.7b04014 • Publication Date (Web): 21 Nov 2017 Downloaded from http://pubs.acs.org on November 22, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Analytical Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 8

Analytical Chemistry Page 1 of 8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

A pumpless acoustofluidic platform for size-selective concentration and separation of microparticles Husnain Ahmed, Ghulam Destgeer, Jinsoo Park, Jin Ho Jung, Raheel Ahmad, Kwangseok Park and Hyung Jin Sung* Department of Mechanical Engineering, KAIST, Daejeon 34141, Korea. E-mail: [email protected] ABSTRACT: We have designed a pumpless acoustofluidic device for the concentration and separation of different sized particles inside a single-layered straight polydimethylsiloxane (PDMS) microfluidic channel. The proposed device comprises two parallel interdigitated transducers (IDTs) positioned underneath the PDMS microchannel. The IDTs produce high-frequency surface acoustic waves that generate semipermeable virtual acoustic radiation force field walls that selectively trap and concentrate larger particles at different locations inside the microchannel and allow the smaller particles to pass through the acoustic filter. The performance of the acoustofluidic device was first characterized by injecting into the microchannel a uniform flow of suspended 9.9 µm diameter particles with various initial concentrations (as low as 10 particles/mL) using a syringe pump. The particles were trapped with ~100% efficiency by a single IDT actuated at 73 MHz. The acoustofluidic platform was used to demonstrate the pumpless separation of 12.0 µm, 4.8 µm, and 2.1 µm microparticles by trapping the 12 µm and 4.8 µm particles using the two IDTs actuated at 73 MHz and 140 MHz, respectively. However, most of the 2.1 µm particles flowed over the IDTs unaffected. The acoustofluidic device was capable of rapidly processing a large volume of sample fluid pumped through the microchannel using an external syringe pump. A small volume of the sample fluid was processed through the device using a capillary flow and a hydrodynamic pressure difference that did not require an external pumping device.

Concentration and separation of particles

and cells is important for a variety of biomedical assays.1,2 The diagnosis of diseases or assessments of therapeutic efficacy require the aggregation or filtration of specific micro-objects, such as circulating tumor cells (CTCs)3–5 or malaria-infected red blood cells6,7, from whole blood. Over the past two decades, several active and passive microfluidic particle manipulation methods8, such as hydrodynamics9, optofluidics10, dielectrophoresis11–13, magnetophoresis14–16, and acoustophoresis17–25, have been developed to capture and isolate target micro-objects. Acoustic forces are preferred, due to their biocompatible nature and ease in microfluidic integration, for microfluidic actuation to provide, for example, chemical gradient generation26, droplet production27, merging28, atomization29,30, particle manipulation31–34 and mixing35–37. Surface acoustic wave (SAW)-based acoustofluidic particle manipulation tools usually comprise a pair of comb-shaped electrodes (interdigitated transducers, or IDTs) patterned on top of a piezoelectric substrate with a PDMS nano/microfluidic channel placed either on top or to the side of the IDT. A single IDT usually produces traveling surface acoustic waves (TSAWs); however, a combination of two IDTs can generate standing surface acoustic waves (SSAWs)38,39 with an acoustic field of periodic pressure nodes and anti-nodes. Fakhfouri et al.40 employed a pair of focused IDTs placed obliquely outside of a microchannel to generate SSAWs within the microfluidic channel that acted as a virtual membrane to concentrate selected particles at the acoustic pressure nodes. Smaller particles permeated through the acoustic field. Collins et al.41 used a focused IDT, positioned

outside of a microchannel and aligned carefully with a microfabricated PDMS membrane inside the microchannel, to concentrate and separate selected particles behind the membrane. A similar focused IDT was used to generate a highly localized acoustic streaming flow for the concentration of submicron particles inside the microfluidic channel without the assistance of a micro-fabricated membrane42. Because IDTs are usually positioned outside of a microchannel, a chunk of the acoustic energy is lost to acoustic damping inside the PDMS walls and only a fraction of the acoustic energy is transferred into the microchannel for useful applications via coupling between the acoustic waves and the fluid. In the acoustofluidic device proposed in this work, the IDTs are placed directly underneath the microchannel to allow the acoustic waves to instantly couple with the fluid and transfer the maximum acoustic energy into the microchannel without incurring significant losses to the PDMS walls. The use of more than one IDTs, placed sequentially along the flow direction and aligned with a simple straight microchannel, provided multiple trapping locations that could separate more than two particle sizes. Most microfluidic devices depend on the use of an external syringe pump to precisely regulate fluid flow inside a microchannel. The concept of pumpless microfluidic platforms has recently gained considerable attention and popularity in the MicroTAS community because eliminating an external pump and tubing enables miniaturization and facilitates the introduction of sample fluids and the integration of various microfluidic gadgets.43,44 Paper-based pumpless microfluidic devices have been proposed in the past; however, the transport of liquid in paper-based devices is limited because paper can vary in its flexibility and bending ability, which disrupts and deforms

ACS Paragon Plus Environment

Analytical Chemistry

Page 2 of 8 Page 2 of 8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

the sample fluid passage.45 Sessile droplet-based open-domain microfluidic platforms that do not require an external pump were demonstrated previously for the concentration46,47 and separation48 of microspheres using SAWs. However, this kind of separation is only useful when post-separation sample collection is not important. In many point-of-care diagnostic applications, concentrated samples can enhance the visual signature of the targeted markers and provide information about the constituents. It is challenging to collect samples after separation of particles in a sessile droplet-based platform because the

flow may be easily disturbed in these open-domain systems during collection of the separated samples using a pipette. The limitations associated with sessile droplet platforms were overcome in the present study using a closed-domain microchannel to process the sample and collect separated particles. The whole operation was carried out without the need for an external pump to run the fluid inside the microchannel, and the concentrated samples could be visualized using the naked eye without a microscope.

Figure 1. Schematic diagram showing the concentration and separation of particles with three different diameters (red, green, and blue). The device was composed of two parallel straight IDTs patterned on top of the LiNbO3 substrate coated with a SiO2 layer, and with a straight PDMS microchannel loosely positioned on top of the substrate without plasma bonding. The top and side views of the device are shown as the concentration zone was enlarged during the SAW off (a) and on (b) modes. The red and green particles slowed down sequentially under the horizontal component of the ARF (Fh) and were concentrated by the vertical component (Fv) at the first and second IDTs, respectively, depending on the particle diameters and the incident acoustic wave frequency. The smaller blue particles were not trapped by the IDTs.

A SAW encountering water radiates a compressional wave through the water (inside the microchannel) at a Rayleigh angle of ~22° (where the microchannel sidewall angle is calculated according to Snell’s law). The particles suspended in the water experience an acoustic radiation force (ARF) that depends strongly on the frequency of the incident wave and the diameter of the particles. The inclined propagation of the acoustic compressional wave inside the microchannel results in two components of the ARF: the horizontal (Fh), and vertical (Fv) components, such that Fv ≅ 2.5Fh. We recently designed a high-throughput particle separation device that effectively utilized the vertical component of the ARF to separate the hydrodynamically focused particles in the vertical plane.49 In the present work, we devised a highly sensitive and efficient SAW-based platform that utilized a similar mechanism of vertically pushing the particles using a stronger ARF to trap and concentrate particles present at extremely low initial particle concentrations (10 particles/mL). This characteristic of the device is chiefly significant for the aggregation and separation of rare biological specimens, such as CTCs, which are not present in abundant amounts inside the blood of an infected individual. We designed a novel SAW-based pump-free particle concentration and separation device to concentrate particles based on their diameters at various locations inside a single-layered PDMS microchannel. This device takes advantage of the vertical component of the ARF to trap large particles while allowing smaller particles to pass through the mixture of microparticles of different sizes. After concentrating the particles in the microchannel, we successfully collected each separated sample at the outlet for further analysis. The proposed device

is simple in its fabrication, handling, and operation due to the exclusion of external equipment, such as pumps, syringes, tubing, pipes, and flow regulators. Our system consists of two parallel IDTs with a straight loosely aligned microchannel positioned perpendicularly to both IDTs and attached to the IDTs via adhesion without plasma bonding. Prior to performing the pumpless separation of particles, we characterized the acoustofluidic device by introducing a uniform flow into the microchannel using a syringe pump, and we demonstrated the versatility of the platform by trapping particles from a very dilute sample with ~100% efficiency. For particle separation, a sample fluid with different particle sizes was introduced into the microchannel with the help of a pipette. Each IDT generated TSAWs that selectively trapped the particles against the flow. Because the IDTs were positioned beneath the microchannel, the vertical force component acted as a virtual wall to trap and concentrate the microspheres. The input frequencies and power were optimized to efficiently concentrate and separate different particle sizes inside the PDMS microchannel without the assistance of a microfabricated membrane. The concentration and separation processes could be visualized with the naked eye without the assistance of a microscope, similar to pregnancy tests and blood glucose test kits, in which colored lines appear and can be seen on a piece of paper.50 The present work is useful for clinical facilities that lack expensive auxiliary equipment. Overall, we demonstrated that different particle sizes could be trapped, concentrated, and separated inside a single-layered PDMS microchannel using the major force component of a TSAW without the need for pumps or external tubing. The device offers several advantages for use in point-of-care diagnostic


Page 3 of 8


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

applications in which the concentration or separation of specific analytes from a biological sample is essential for further sample analysis. First, device operation could be visualized without a microscope. Second, the position of the aggregated sample could be shifted inside the channel by precisely controlling the input power. Third, each concentrated colony of different particle sizes could be collected at the outlet for further analysis. Fourth, the disposable PDMS microfluidic chip could be replaced with a new one and the IDTs could be reused.

EXPERIMENTAL SECTION Device fabrication: The acoustomicrofluidic platform consisted of a SAW device and a straight single-layered PDMS microchannel. Two parallel IDTs having a total aperture of 1.5 mm and 20 electrode finger pairs with uniform widths and gaps (1st IDT, λ/4 = 12.5 µm; 2nd IDT, λ/4 = 6.5 µm) were deposited onto a LiNbO3 substrate (500 µm thick; MT Korea, Korea), followed by the deposition of a thin layer of SiO2 (2000 Å) to prevent mechanical damage to the electrodes. A PDMS microchannel was fabricated using common soft lithography processes. An SU-8 (photoresist) layer of the desired thickness was spin-coated and patterned by UV exposure on top of a silicon substrate that acted as a mold for the microchannel. The PDMS base and curing agent (Sylgard 184A and 185B, Dow Corning, U.S.A) were mixed and poured into the developed SU-8 mold. After curing at 65°C for 1 hour, the PDMS microchannel was peeled away from the surfacetreated silanized substrate (trichloro silane; Sigma-Aldrich, U.S.A). The width and height of the microchannel were 750 µm and 140 µm, respectively. The inlet reservoir was made by punching a hole of 4 mm using a punching tool (Harris UniCore), and the outlet was opened by slicing the end of the microchannel using a cutter. After making the inlet port and outlet opening, the microfluidic channel was loosely aligned on top of the IDTs without plasma bonding. Experimental setup: The acoustomicrofluidic device was mounted on the stage of a fluorescent microscope (BX53, Olympus Japan). The IDTs were actuated using two RF signal generators (N5181A, Agilent Technologies, U.S.A; N5171B, Keysight Technologies, USA), which produced AC signals at 73 MHz and 140 MHz frequency. Two amplified (LZT-22+, Mini-Circuits, U.S.A; ZHL-100W-GAN+, Mini-Circuits, USA) signals of 120–500 mW were fed into the device. A sample mixture of particles having different diameters was added to the inlet reservoir with the help of a pipette. Experimental images were captured using a CCD camera (DP72, Olympus, Japan) and were processed using ImageJ (http://imagej.nih.gov/ij/) to improve visualization. The separated particles were collected by placing a micro pipe at the outlet and were analyzed using a c-chip disposable hemocytometer (Digital Bio, Korea). Particle solution preparation: Five differently sized (12 µm, 9.9 µm, 6.0 µm, 4.8 µm, and 2.1 µm) polystyrene particles (36-3, G1000, 36-2, G0500, B0200 Thermo Scientific, CA, USA) having the same density (1.05 g/cm3) were used in the present study to demonstrate the particle trapping, concentration, and separation mechanisms. Each of the particle solutions consisted of 1% solid microspheres per microliter liquid. The total number of beads/µL was counted at a specific particle

concentration in the sample solution, which contained 47.5% DI water, 47.5% deuterium oxide (D2O), and 5% surfactant. The addition of D2O matched the density of the PS particles with the sample solution. Surfactant (Photo-Flo 200 solution; Eastman Kodak Company, USA) was added to prevent particle adhesion to the microchannel surface and cohesion among the particles.

WORKING MECHANISM The schematic diagram of the pumpless microfluidic device illustrates the PDMS microchannel positioned on top of the piezoelectric substrate (lithium niobate, LiNbO3) onto which were deposited two IDTs (see Figure 1). A straight microfluidic channel with one inlet port and one outlet opening was loosely aligned with the IDTs and placed directly on top of the IDTs without plasma bonding. A few microliters of ethanol were initially injected through the inlet well with the help of a pipette to reduce the surface tension within the PDMS microchannel by wetting the walls.51 Next, an inlet well was filled with a sample solution containing particles of different diameters (fluorescent red, green, and blue particles). The particles flowed through the microchannel under the hydrodynamic pressure generated by the height of the inlet well and the capillary action inside the microchannel.52 During the SAW off mode, the particle mixture flowed through the microchannel unaffected and was collected at the outlet opening, resulting in no particle separation or concentration (see Figure 1(a)). The ARF’s action on particles strongly depends on the particle diameter and the TSAW frequency. This dependency is characterized by a dimensionless Helmholtz number (ߢ), defined as ߢ = ߨ݂݀/ܿ௙ , where ݀ is the particle diameter, ݂ is the TSAW frequency, and ܿ௙ is the speed of sound in the fluid.53–56 The TSAW frequency of the first IDT and the set of particle diameters were chosen such that ߢ > 1 for red particles and ߢ < 1 for green and blue particles. For the second IDT, ߢ > 1 for green particles and ߢ < 1 for blue particles. The value of the ߢ-factor for the smallest (blue) particles was less than one under both IDTs to minimize the effect of the ARF on these particles. During the SAW on mode, two different particle sizes with ߢ > 1 (red and green) were trapped and concentrated in the vicinities of the first and second IDTs, respectively, due to the ARFs generated from each IDT. The smallest particles with ߢ < 1 were nearly unaffected by the ARF and were collected through the outlet. Note that the horizontal (x-direction) component of the ARF ‫ܨ‬௛ was almost balanced with the drag force ‫ܨ‬ௗ on the particle; however, the vertical (y-direction) component of the ARF ‫ܨ‬௩ pushed the particles in the upward direction against the microchannel ceiling and ceased their motion. As a result, two different particle sizes (red and green) were concentrated at specific regions inside a single-layered microchannel whereas the smallest (blue) particles were ultimately collected through the outlet (see Figure 1(b)). The trapped particles were subsequently released and collected at the outlet by turning off the second and first IDTs, respectively.

RESULTS AND DISCUSSION Concentration of particles by TSAWs: The particle trapping capability of the device was characterized by pumping a sample solution containing similarly sized




1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

polystyrene particles (9.9 µm fluorescent green) at a uniform flow rate (Q: 1000 µL/hr) through the microchannel as the particles were concentrated using a single IDT actuated at 73 MHz. The ߢ-value for the 9.9 µm particles (green) exposed to 73 MHz frequency acoustic waves was calculated to be 1.5, ensuring that the particles experienced a strong ARF and were stopped at the IDT. The solution containing no particle was collected at the outlet. The concentration of the particles by the TSAWs is shown in video S1. The hemocytometer images of the sample added to the inlet and the sample collected at the outlet, shown in Figure 2, confirmed that all suspended particles were trapped inside the device. The trapping performance of the device was further characterized (with respect to time) by changing the initial concentration of particles in the sample solution. At a constant input power and flow rate, the time required to

achieve a fixed trapping concentration increased as the initial sample concentration decreased. For an initial sample concentration of 400 particles/µL, the particles were gradually trapped inside the microchannel, and the intensity of the trapped particles increased over time, from 1 sec to 30 sec, corresponding to an increase in the concentration of particles trapped inside the microchannel (see Figure 3(A, B)). Similarly, experiments were performed using initial sample concentrations of 200 particles/µL, 100 particles/µL, 20 particles/µL, 10 particles/µL, and 1 particle/µL, as shown in Figures S1–S5, respectively. As the number of particles per microliter decreased from 400 to 1, the time required to achieve the same intensity (concentration) increased from 0.38 min to 118 min (see Figure 3(C)).

Figure 2. Schematic diagram of the microchannel, along with an experimental image of the particles (9.9 µm green fluorescent) concentrated inside the microchannel due to the ARF (middle). Hemocytometer images of the inlet sample solution and the outlet collected sample, illustrating the efficient concentration of microspheres inside the microfluidic channel (left and right). Scale bar: 250 µm.

Particle trapping from an extremely low initial sample concentration: The high sensitivity of the proposed SAW device for capturing particles from an extremely lowconcentration sample solution was demonstrated by pumping a sample solution containing 10 particles/mL (9.9 µm, green) through the microchannel. The experiment was run for two hours at a flow rate of 5 mL/hr, with the goal of trapping 100 particles from a 10 mL solution. The images captured over a time lapse of 10 min revealed that almost all particles were successfully trapped and concentrated beside the IDT (see

Figure 4). After 1 min of the process, 1 particle was captured. The number of particles captured gradually increased to nearly half (~50) of the target particles after 1 hr, and to 99 particles out of 100 targeted particles after 2 hrs. The particles were counted manually using the images presented in Figure 4, with a constant time gap between frames, after size dilation of the particles using the ImageJ software to improve visualization. The trapping of extremely low concentrations of particles can be seen in video S2.


Page 5 of 8


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3. Characterization of the particle trapping concentration inside the microchannel, for various initial sample concentrations. (A) Experimental images showing top views of the microchannel as the particles were gradually trapped from an initial sample concentration of 400 particles/µL. (B) The graph shows a linear increase in the trapped particle concentration (intensity) from 1 sec to 30 sec. (C) The bar chart illustrates that a decrease in the number of particles per microliter in the sample solution increased the time required to achieve the fixed trapping concentration. Scale bar: 250 µm.

Figure 4. Efficient particle trapping from an extremely low-concentration particle solution. The initial concentration of the sample solution was 10 particles/mL. 99 out of 100 targeted particles were captured in 2 hrs. Scale bar: 250 µm.

A pumpless device for the concentration and separation of particles: In addition to characterizing particle trapping and concentration, we developed a pump-free acoustofluidic device for concentrating and separating particles of different sizes that could be operated without a microscope. A mixture of microspheres was concentrated and separated using two parallel IDTs positioned beneath the straight microfluidic channel. An inlet well was used to introduce the sample solution to the device, and the outlet opening was created by slicing the PDMS microchannel at the opposite side (see Figure 5). After injecting 20 µL ethanol to wet the microchannel walls, a 100 µL solution containing three different particle sizes (12 µm red, 4.8 µm green, and 2.1 µm blue) was introduced into the inlet well with the help of a pipette. The particles flowed through the microchannel at a stable velocity that depended on the height of the inlet well. When the device was actuated, the 12 µm (red) particles were concentrated adjacent to the first

IDT (݂ = 73 MHz) due to the direct ARF, as ߢ > 1 for red particles and ߢ < 1 for green and blue particles. Similarly, 4.8 µm (green) particles were concentrated adjacent to the second IDT (݂ = 140 MHz), as ߢ > 1 for green particles and ߢ < 1 for blue particles. The experimental results demonstrated that the 12 µm red and 4.8 µm green particles were concentrated in a chromatographic style beside the first and second IDTs, respectively, whereas the 2.1 µm blue (smallest) particles exited the microchannel unaffected (see Figure 5(A)). After processing 100 µL of the sample solution, a similar volume of ethanol was injected using the pipette to wash the microfluidic channel. Figure 5(B) shows the concentrated particles in red and green bands at specific locations inside the microchannel after washing (also see video S3). We also demonstrated the concentration of 9.9 µm and 6.0 µm particles inside a microfluidic channel (see Figure S6).

Figure 5. Experimental images of particles of different diameters concentrated at distinct locations inside the microchannel. (A) Power on: blue particles passed through the microchannel unaffected, whereas the red and green particles were trapped. (B) Power on: after washing with ethanol, red and green particle bands were clearly observed. (C) Naked eye view (without a magnification lens) of the concentrated (different diameter) particles inside the microchannel. (D) Hemocytometer images displaying the separated particle samples collected at the outlet of the microchannel. Scale bar: 250 µm.




1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Naked eye view of the device operation, sample collection, and separation analysis: The proposed device can be operated without the need for a microscope or a syringe pump, thereby reducing external equipment requirements. A naked eye view of the device shown in Figure 5(C) clearly reveals that the red (12 µm) and green (4.8 µm) particles were concentrated inside the microchannel to produce two distinctly colored bands while a purified sample of 2.1 µm (blue) particles was collected at the outlet using a tube (see Figure S7). The collection of the concentrated red and green particles was achieved after washing the microfluidic channel with ethanol, as described earlier, while the IDTs were operated. The second IDT (140 MHz) was turned off first to release the green particle band, and the green particles were then collected at the outlet in a fashion similar to blue particle collection. Next, the first IDT (73 MHz) was turned off, and the red particles were collected at the outlet. In this way, red, green, and blue particles were collected in separate tubes at the outlet for separation analysis. A naked eye view of the particle trapping, concentration, washing, and release steps is presented in video S4. A hemocytometer was used to measure the purities (100%, 95%, and 70% of the collected blue, green, and red particles, respectively) of each collected sample (see Figure 5(D)). The polystyrene particles exposed to high-frequency acoustic waves experienced a direct ARF due to asymmetric scattering of the incident acoustic wave, and they vibrated to release a secondary acoustic field. The vibrating microspheres formed a secondary attractive force field around them to capture smaller beads that were unaffected by the direct ARF. The targeted red particles were concentrated adjacent to the first IDT due to the direct effects of the ARF, whereas no primary ARF acted on the non-target green and blue particles, as the acoustic wavelength was much longer than the non-target particle size, resulting in ߢ < 1. Nevertheless, the formation of the secondary force field around the vibrating red particles trapped green and blue particles in an undesirable manner around the red particles and decreased the purity (70%) of the concentrated red particles. In addition to being trapped by the second IDT, the green particles aggregated under the ARF. Although blue particles (undesired) remained unaffected by the primary ARF, they were captured in the field of the concentrated green particles due to the secondary ARF, which decreased the green particle purity to 95%. No red particles passed the first IDT, and no green particles passed the second IDT; therefore, the blue particles were collected at the outlet with 100% purity. The reduced purities of the concentrated green and red particle samples were attributed to the secondary acoustic radiation force field.

CONCLUSION We demonstrated a novel acoustofluidic technique for concentrating and separating particles of different diameters inside a single-layered microchannel without the assistance of a microfabricated membrane. Particles from an extremely lowconcentration solution could be detected, trapped, and concentrated in a highly efficient manner inside the microchannel. This device functionality is particularly useful for concentrating and isolating specific low-abundance targets, such as CTCs, which are present in very small numbers (1– 10/mL) in patient blood. The ARF generated by the TSAWs acted as a virtual wall for the concentration of selective

particles in the microchannel while allowing non-target particles to pass through it. The proposed method is noncontact, noninvasive, and label-free. These features are particularly significant for biochemical assays. The present acoustofluidic chip does not require the induction of external pumping action to inject a sample solution into the microchannel. Moreover, the operation of this device (trapping, concentration, separation) can be visualized without a microscope. These device characteristics reduce the need for external equipment and could be useful for point-of-care testing applications.

ASSOCIATED CONTENT Supporting Information Additional materials are provided in the form of a PDF file. The Supporting Information is available free of charge on the ACS Publications website.

AUTHOR INFORMATION Corresponding Author *Email: [email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the KUSTAR-KAIST Institute, the Creative Research Initiatives (no. 2017-013369) program of the National Research Foundation of Korea (MSIP), and the Korea Polar Research Institute (KOPRI).

REFERENCES (1) (2) (3) (4) (5)

(6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)

Wyatt Shields IV, C.; Reyes, C. D.; López, G. P. Lab Chip 2015, 15 (5), 1230–1249. Sajeesh, P.; Ashis, @bullet; Sen, K.; Sen, A. K. Microfluid. Nanofluidics 2014, 17 (1), 1–52. Harouaka, R. A.; Nisic, M.; Zheng, S.-Y. J. Lab. Autom. 2013, 18 (6), 455–468. Yu, M.; Stott, S.; Toner, M.; Maheswaran, S.; Haber, D. A. J. Cell Biol. 2011, 192 (3), 373–382. Maheswaran, S.; Sequist, L. V; Nagrath, S.; Ulkus, L.; Brannigan, B.; Collura, C. V; Inserra, E.; Diederichs, S.; Iafrate, A. J.; Bell, D. W.; Digumarthy, S.; Muzikansky, A.; Irimia, D.; Settleman, J.; Tompkins, R. G.; Lynch, T. J.; Toner, M.; Haber, D. A. N. Engl. J. Med. 2008, 359 (4), 366–377. Trang, D.; Huy, N.; Kariu, T.; Tajima, K.; Kamei, K. Malar. J. 2004, 3 (1), 7. Nam, J.; Huang, H.; Lim, H.; Lim, C.; Shin, S. Anal. Chem. 2013, 85 (15), 7316–7323. Bhagat, A. A. S.; Bow, H.; Hou, H. W.; Tan, S. J.; Han, J.; Lim, C. T. Med. Biol. Eng. Comput. 2010, 48 (10), 999–1014. Wu, Z.; Hjort, K. Micro Nanosyst. 2009, 1 (3), 181–192. Jung, J. H.; Lee, K. H.; Lee, K. S.; Ha, B. H.; Oh, Y. S.; Sung, H. J. Microfluid. Nanofluidics 2014, 16 (4), 635–644. Zhang, C.; Khoshmanesh, K.; Mitchell, a; Kalantar-Zadeh, K. Anal. Bioanal. Chem. 2010, 396 (1), 401–420. Mathew, B.; Alazzam, A.; Destgeer, G.; Sung, H. J. H. J. J. Electrostat. 2016, 84, 63–72. Alazzam, A.; Mathew, B.; Alhammadi, F. J. Sep. Sci. 2017, 40 (5), 1193–1200. Pamme, N.; Wilhelm, C. Lab Chip 2006, 6 (8), 974–980. Park, J. W.; Lee, N. R.; Cho, S. M.; Jung, M. Y.; Ihm, C.; Lee, D. S. ETRI J. 2015, 37 (2), 233–240. Ngamsom, B.; Esfahani, M. M. N.; Phurimsak, C.; LopezMartinez, M. J.; Raymond, J.-C.; Broyer, P.; Patel, P.; Pamme,


Page 7 of 8


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(17) (18) (19)

(20) (21) (22) (23)

(24)

(25) (26) (27) (28) (29) (30) (31)

(32) (33) (34) (35) (36)

N. Anal. Chim. Acta 2016, 918, 69–76. Destgeer, G.; Lee, K. H.; Jung, J. H.; Alazzam, A.; Sung, H. J. Lab Chip 2013, 13 (21), 4210. Collins, D. J.; Ma, Z.; Han, J.; Ai, Y. Lab Chip 2017, 17 (1), 91–103. Wu, M.; Mao, Z.; Chen, K.; Bachman, H.; Chen, Y.; Rufo, J.; Ren, L.; Li, P.; Wang, L.; Huang, T. J. Adv. Funct. Mater. 2017, 27 (14), 1606039. Park, J.; Jung, J. H.; Destgeer, G.; Ahmed, H.; Park, K.; Sung, H. J. Lab Chip 2017, 17 (6), 1031–1040. Jung, J. H.; Destgeer, G.; Park, J.; Ahmed, H.; Park, K.; Sung, H. J. Anal. Chem. 2017, 89 (4), 2211–2215. Shi, J.; Ahmed, D.; Mao, X.; Lin, S.-C. S.; Lawit, A.; Huang, T. J. Lab Chip 2009, 9 (20), 2890–2895. Chen, Y.; Nawaz, A. A.; Zhao, Y.; Huang, P.-H.; McCoy, J. P.; Levine, S. J.; Wang, L.; Huang, T. J. Lab Chip 2014, 14 (5), 916–923. Wu, M.; Ouyang, Y.; Wang, Z.; Zhang, R.; Huang, P.-H.; Chen, C.; Li, H.; Li, P.; Quinn, D.; Dao, M.; Suresh, S.; Sadovsky, Y.; Huang, T. J. Proc. Natl. Acad. Sci. 2017, 114 (40), 10584– 10589. Tan, M. K.; Friend, J. R.; Yeo, L. Y. Lab Chip 2007, 7 (5), 618– 625. Destgeer, G.; Im, S.; Ha, B. H.; Ho Jung, J.; Ahmad Ansari, M.; Sung, H. J. Appl. Phys. Lett. 2014, 104 (2), 23506. Collins, D. J.; Alan, T.; Helmerson, K.; Neild, A. Lab Chip 2013, 13 (16), 3225–3231. Sesen, M.; Alan, T.; Neild, A. Lab Chip 2014, 14 (17), 3325– 3333. Tveen-Jensen, K.; Gesellchen, F.; Wilson, R.; Spickett, C. M.; Cooper, J. M.; Pitt, A. R. Sci. Rep. 2015, 5 (1), 9736. Cortez-Jugo, C.; Qi, A.; Rajapaksa, A.; Friend, J. R.; Yeo, L. Y. Biomicrofluidics 2015, 9 (5), 52603. Mao, Z.; Li, P.; Wu, M.; Bachman, H.; Mesyngier, N.; Guo, X.; Liu, S.; Costanzo, F.; Huang, T. J. ACS Nano 2017, 11 (1), 603– 612. Chen, Y.; Wu, M.; Ren, L.; Liu, J.; Whitley, P. H.; Wang, L.; Huang, T. J. Lab Chip 2016, 16 (18), 3466–3472. Destgeer, G.; Jung, J. H.; Park, J.; Ahmed, H.; Park, K.; Ahmad, R.; Sung, H. J. RSC Adv. 2017, 7 (36), 22524–22530. Destgeer, G.; Ha, B. H.; Jung, J. H.; Sung, H. J. Lab Chip 2014, 14 (24), 4665–4672. Shilton, R. J. R.; Tan, M. K. M. K.; Yeo, L. Y. L. Y.; Friend, J. R. J. R. J. Appl. Phys. 2008, 104 (1), 14910. Huang, P.-H.; Chan, C. Y.; Li, P.; Nama, N.; Xie, Y.; Wei, C.-

(37) (38) (39) (40) (41) (42) (43) (44) (45) (46) (47) (48) (49) (50) (51)

(52) (53) (54) (55) (56)

H.; Chen, Y.; Ahmed, D.; Huang, T. J. Lab Chip 2015, 15 (21), 4166–4176. Huang, P.-H.; Xie, Y.; Ahmed, D.; Rufo, J.; Nama, N.; Chen, Y.; Chan, C. Y.; Huang, T. J. Lab Chip 2013, 13 (19), 3847. Destgeer, G.; Sung, H. J. Lab Chip 2015, 15 (13), 2722–2738. Franke, T.; Abate, A. R.; Weitz, D. A.; Wixforth, A. Lab Chip 2009, 9 (18), 2625. Fakhfouri, A.; Devendran, C.; Collins, D. J.; Ai, Y.; Neild, A. Lab Chip 2016, 16 (18), 3515–3523. Collins, D. J.; Alan, T.; Neild, A. Appl. Phys. Lett. 2014, 105 (3), 33509. Collins, D. J.; Ma, Z.; Ai, Y. Anal. Chem. 2016, 88 (10), 5513– 5522. Shilton, R. J.; Travagliati, M.; Beltram, F.; Cecchini, M. Appl. Phys. Lett. 2014, 105 (7), 74106. Abaci, H. E.; Gledhill, K.; Guo, Z.; Christiano, A. M.; Shuler, M. L. Lab Chip 2015, 15 (3), 882–888. Li, X.; Ballerini, D. R.; Shen, W. Biomicrofluidics 2012, 6 (1), 11301–1130113. Destgeer, G.; Cho, H.; Ha, B. H.; Jung, J. H.; Park, J.; Sung, H. J. Lab Chip 2015, 16 (4), 660–667. Li, H.; Friend, J. R.; Yeo, L. Y. Biomed. Microdevices 2007, 9 (5), 647–656. Destgeer, G.; Jung, J. H.; Park, J.; Ahmed, H.; Sung, H. J. Anal. Chem. 2017, 89 (1), 736–744. Ahmed, H.; Destgeer, G.; Park, J.; Jung, J. H.; Sung, H. J. Adv. Sci. 2017, in press, doi:10.1002/advs.201700285. Mark, D.; Haeberle, S.; Roth, G.; von Stetten, F.; Zengerle, R. Chem. Soc. Rev. 2010, 39 (3), 1153–1182. Shirani, E.; Razmjou, A.; Tavassoli, H.; Landarani-Isfahani, A.; Rezaei, S.; Abbasi Kajani, A.; Asadnia, M.; Hou, J.; Ebrahimi Warkiani, M. Langmuir 2017, 33 (22), 5565–5576. Lynn, N. S.; Dandy, D. S. Lab Chip 2009, 9 (23), 3422. King, L. V. Proc. R. Soc. A Math. Phys. Eng. Sci. 1934, 147 (861), 212–240. Hasegawa, T.; Yosioka, K. J. Acoust. Soc. Am. 1969, 46 (5B), 1139–1143. Destgeer, G.; Ha, B. H.; Park, J.; Jung, J. H.; Alazzam, A.; Sung, H. J. Phys. Procedia 2015, 70, 30–33. Destgeer, G.; Ha, B. H.; Park, J.; Jung, J. H.; Alazzam, A.; Sung, H. J. In Analytical Chemistry; 2015; Vol. 87, pp 4627– 4632.


Page 8 of 8


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

For TOC only


Page 8 of 8

A pumpless acoustofluidic platform for size ... - ACS Publications

Recommend Documents