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Hybrid optothermal and acoustic manipulations of microbubbles for precise and on-demand handling of micro-objects
Accepted Manuscript Title: Hybrid optothermal and acoustic manipulations of microbubbles for precise and on-demand handling of micro-objects Authors: Jae Hun Shin, Jeonghwa Seo, Jiwoo Hong, Sang Kug Chung PII: DOI: Reference:
S0925-4005(17)30269-1 http://dx.doi.org/doi:10.1016/j.snb.2017.02.049 SNB 21780
To appear in:
Sensors and Actuators B
Received date: Revised date: Accepted date:
12-12-2016 3-2-2017 9-2-2017
Please cite this article as: Jae Hun Shin, Jeonghwa Seo, Jiwoo Hong, Sang Kug Chung, Hybrid optothermal and acoustic manipulations of microbubbles for precise and on-demand handling of micro-objects, Sensors and Actuators B: Chemical http://dx.doi.org/10.1016/j.snb.2017.02.049 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Hybrid optothermal and acoustic manipulations of microbubbles for precise and on-demand handling of micro-objects Jae Hun Shin†1, Jeonghwa Seo†1, Jiwoo Hong2*, Sang Kug Chung1* 1
Department of Mechanical Engineering, Myongji University, Yongin, Gyeonggido, South Korea
2
Department of Mechanical Engineering, Pohang University of Science and Technology
(POSTECH), San 31, Hyoja-dong, Pohang 790-784, South Korea
Co-corresponding Authors *
Phone: +82-31-330-6346. Fax: +82-31-330-6957. E-mail: [email protected].
*
Phone: +82-54-279-8201. Fax: +82-54-279-5899. E-mail: [email protected].
†These authors contributed equally to this work. 1
Graphical abstract
Research Highlights
For precise and on-demand handling of micro-objects, we propose the integrated strategy combining strengths of optothermal and acoustical handling strategies.
Microbubbles can be optothermally generated, and their size can be tuned by controlling the illumination time and power of a laser beam.
The bubbles can be delivered into a preferred position through optothermocapillary flow.
Micro-objects with two different sizes can be selectively separated, and then only a micro-object with a specific size can be collected through a secondary acoustic radiation and a streaming flow generated from an acoustically oscillating bubble.
Abstract Manipulating specific micro-objects (e.g., colloidal particles and microorganisms) precisely and selectively in liquid medium is of great importance in myriad engineering fields. We here develop a hybrid technique for micromanipulation of micro-objects by incorporating optothermally and acoustically excited bubble on-demand. The integrated strategy combines strengths of optothermal (e.g., precise size control in bubble creation and easy delivery of micro-objects into target position) and acoustical (e.g., on-demand capturing and precise sorting of micro-objects) strategies. Microbubbles can be optothermally generated, and their size can be regulated by tuning the illumination time and power of a laser beam. The bubbles can be delivered into a preferred position 2
through optothermocapillary flow. Sequentially, micro-objects with two different sizes can be selectively separated, and then only a micro-object with a specific size can be collected through a secondary acoustic radiation and a streaming flow generated from an acoustically oscillating bubble. To emulate on-demand manipulation of bio-objects in technological applications, we examine a fullstep manipulation process of micro-objects, which consists of generating bubbles and sorting/capturing/carrying/releasing of desired micro-objects under optothermal and acoustical actuations. The hybrid manipulation technique can be a good alternative technology to conventional ones and thus can be utilized in biological applications and micro-device assembly. Keywords: Micromanipulation of micro-objects; Bubble oscillation; Secondary acoustic radiation; Microstreaming flow; Optothermocapillary flow
1. Introduction The precise and on-demand handling (e.g., trapping/releasing, sorting, and carrying) of micro-objects (e.g., colloidal particles, cells, and microorganisms) in liquid medium is mightily important in various fields of academic research and engineering applications, such as biology, chemistry, physics, materials, and medicine [1,2]. Diverse techniques for handling micro-objects have been proposed based on optical [3-5] (or optoelectronical [6-9]), electrical [10-13], magnetic [14-16], mechanical [14-16], thermal [17-21], and acoustic [22-24] and hydrodynamic [25-27] forces. Among such existing techniques, an acoustic field-based technique, especially a bubble-mediated acoustical actuation, has shown potential as an effective handling strategy for microfluidic and biofluidic applications [28,29]. Bubble-mediated technique can manipulate samples, such as cells and microorganisms, without any unwanted damage caused by electric or magnetic fields and without cross-contamination caused by direct contact between the manipulator and samples [29]. When a bubble oscillates under the action of an acoustic field, it autonomously radiates a secondary sound field and simultaneously generate a streaming flow around it [29-32]. Accordingly, neighbouring objects around the bubbles experience two forces—secondary radiation force (Frad) 3
caused by the secondary sound field and drag force (Fdrag) caused by the streaming flow [29-32]. As a result, the motion of the objects is determined by a competition between Frad and Fdrag, and it is affected by physical parameters, such as bubble and object sizes, frequency of acoustic excitations, and densities of objects and liquid medium [28,29]. The competition between the two forces and the resulting motion of objects will be explained in detail in the Results and discussion section. On the basis of the remarkable features of an oscillating bubble, many researchers have developed a myriad of microfluidic devices, including fluidic regulators (e.g., micropump and micromixer) and micro-object manipulator (e.g., filter, transporter, microrotor, and micropropeller), as well as biological (or biomedical) applications (e.g., cell lysis, and drug and gene delivery) [28,29]. We have also developed oscillating bubble-based microfluidic components (e.g., micropump [33], manipulator [34-41], micromixer [42] and micromotor [43]), biomedical applications (e.g., drug delivery [44] and ultrasound contrast agents [45]), and energy harvesting system [46]. The bubble oscillation-based microfluidic applications were well summarized in review papers [28,29,47] and recently published papers [48-50]. In spite of these considerable efforts, technological limitations still exist on precision and ondemand control over the size and position of the generated bubble. To solve those, Xie et al. [51] first demonstrated dynamic control of optothermal bubble generation by tuning the power and position of a laser focused on a gold film and subsequently trapped the cells through acoustic radiation forces by applying acoustic waves. Their proposed method (called as optoacoustic tweezers) has many advantages such as programmable and biocompatible cell manipulation, and easy integration into microfluidic units. Furthermore, they showed bubble generation and particle manipulation (e.g., trapping and carrying) via the bubble by only incorporating optothermal effects [52]. Nevertheless, their techniques can still be developed. For instance, the development of a fully integrated technique that combines strengths of acoustic and optothermal manipulation is required for further precise and on-demand handling of samples. 4
Thus, we here propose a hybrid microbubble-based manipulation technique for precise and on-demand handling of micro-objects by synergistically combining optothermal and acoustical strategies. The optothermal strategy allows for precise control over the size of the generated bubble, as well as facile transportation of the bubble. On the other hand, the acoustical strategy enables the capture (or release) and separation of samples on-demand. Figure 1 illustrates the schematic diagram of micromanipulation of micro-objects by utilizing optothermally and acoustically excited bubble. When a laser beam is focused onto the bottom substrate covered with an amorphous silicon layer of microfluidic chip, the generation and growth of a microbubble on the illustrated spot occurs due to optothermal effects [Figs. 1(a) and 1(b)]. The bubble can be transported toward near the microparticles with two different sizes by controlling the laser beam due to optothermocapillary effects [Fig. 1(c)]. When the bubble oscillates around its resonant frequency under an acoustical excitation, it can attract large microparticles while can repulse small ones due to competition between acoustic radiation and drag forces [Fig. 1(d)]. The bubble loaded with large microparticles can be transported to a preferred position under both optothermal and acoustical actuations [Fig. 1(e)]. After the bubble arrives at the chosen position, it can release large microparticles by ceasing an acoustic actuation, and subsequently, it can return to its original position by optothermocapillary effects [Fig. 1(f)]. The principle of each operation that involves the proposed on-chip manipulation will be explained thoroughly in the Results and discussion section.
2. Experimental details To demonstrate micromanipulation of micro-objects by utilizing an optothermally and acoustically excited bubble, a microfluidic chip consisting of top and bottom glass plates was fabricated by the following procedure. First, an amorphous silicon layer with 500 nm thickness was deposited onto the bottom glass plate (75 mm in length × 25 mm in width) by low-pressure deposition of chemical vapor, as illustrated in Figs. 2(a) and 2(b). Subsequently, the top and bottom 5
plates were treated by cleaning system of ultraviolet ozone (Jelight Company Inc., USA) to produce hydrophilic surfaces, thereby minimizing the contact area between the bubble and the plates [Figs. 2(c)–(e)]. Finally, a small amount of water was poured into an acrylic chamber (7.5 cm in length × 2.5 cm in width × 0.5 cm in height), and subsequently, the top plate was gently placed on top of the bottom plate, separated by a spacer with 250 μm in height at the end edges [Fig. 2(f)].
Figure 3 illustrates schematic diagram of the overall experimental setup for manipulation of objects in the fabricated microfluidic chip. For optothermally-induced generation of a microbubble, the Nd: YAG laser beam with 532 nm wavelength (Changchun New Industries Optoelectronics Tech. Co., China) was guided through a plane mirror (Nd: YAG laser line mirror, Edmund Optics, USA) and was focused onto an amorphous silicon layer of the bottom plate. Here, the focused laser beam has a diameter of about 500 μm. For the movement of the generated microbubble by optothermocapillary effects, a 2D motorized translation stage (Edmund Optics, USA) was used to change the position of laser beam irradiation. For a manipulation of micro-objects via an acoustically-agitated microbubble, AC electrical signals, produced by a function generator (33210A, Agilent Co., USA) and then amplified (BA4825, NF Co., Japan), were applied to a piezoactuator (PIC151, Physik Instruments Inc., Germany) attached to the side wall of the acrylic chamber. The dynamic behavior of a bubble and micro-objects (glass beads with a 10 and 100 μm diameter; Sigma, USA) was sequentially recorded by using a charge-coupled device camera (EO-1312C, Edmund Optics, USA) and a high-speed camera (Phantom Miro eX2, Vision Research, USA). Every experiment was repeated at least five times, and the data presented in the Results and discussion section are the average of the results.
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3. Results and discussion When a laser beam (532 nm wavelength) generated from a Nd: YAG laser is focused onto an amorphous silicon layer (500 nm in thickness), which acts as a light absorber, deposited on the bottom plate, a microbubble is generated and gradually expanded by optothermal effect. Figure 4 illustrates the temporal variation in the size of optothermally-generated bubbles during irradiation of laser beams with different powers of 500, 600, and 700 mW. We can reproducibly generate bubbles with diameters that range from 260 μm to 840 μm. After sudden birth of a microbubble with specific size, the size of the generated microbubble is almost linearly proportional to the illumination time of a laser beam and is increased by the laser power. When a laser power is larger than certain threshold value (500 mW in the present work), the water on the focusing spot of laser beam reaches its boiling point and resultantly a microbubble is generated. Subsequently, the bubble thermally grows and its size increases almost linearly with the illumination time. This tendency is similar to that reported by previous studies [51, 53, 54]. In addition, the generated bubble stably stays on the amorphous silicon layer during its expansion. These results are similar to those reported in previous works [51, 52]. Different from those works, however, sudden shrinkage of the bubble after turning off the laser power is hardly observed, which may result from the following reasons: First, bubble shrinkage is due to gas diffusion from the bubble, which accelerates as the bubble becomes smaller [55]. The size of an optothermally-generated bubble reported in previous works is considerably smaller than that observed in the present work. Second, an amorphous silicon layer as a light absorber used in the present work has a lower thermal conductivity than the gold film used in previous works [56]. Accordingly, its temperature does not suddenly decrease, thereby maintaining its size stably even though the laser power is turned off. Consequently, we can precisely control the size of the generated bubble by tuning the illumination time and power of the laser beam, and stably manipulate the bubble.
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The optothermally-generated bubble can be transported toward a target position by using optothermocapillary effects, as shown in Fig. 5. A bubble with 300 μm diameter is preferentially generated by illuminating a laser beam with 600 mW power onto the light absorbing substrate, as shown in Fig. 4. When a 300 mW power laser beam is focused onto the region in the vicinity of the bubble, the optically-induced heating of the absorbing substrate generates a thermal gradient around the bubble. The temperature gradient creates a gradient of surface tension, which drives a fluid flow from heating to non-heating regions [57]. As a result, the bubble moves toward the optical heating region. This phenomenon is called optothermocapillary effect [58-62]. When the position of a laser beam is moved by a motorized, the bubble follows the position of the laser spot. On the other hand, when the laser power is turned off, the bubble is released at the target position. Note that, compared with the power (600 mW) used to generate a bubble, a lower power of the laser (300 mW) was employed to transport a bubble, thereby minimizing the unwanted change of bubble volume by bubble expansion or any damage of a microchip. As mentioned in the Introduction, it is well-known phenomenon that when a bubble oscillates through acoustic excitation, it radiates a secondary sound field and simultaneously generates a streaming flow around it. Therefore, micro-objects around the oscillating bubble undergo a secondary radiation force (attractive or repulsive force) by the radiated sound field and a drag force by the streaming flow. For an oscillating bubble and a rigid spherical particle, the secondary radiation force (Frad) and viscous drag force (Fdrag) are estimated by the following equations:
f p f 2 b 2 Rb 6 Rp3 Frad 4f 2 d5 p f
(1)
Fdrag 6 RpUs
(2)
8
where ρf is the density of the ambient fluid, ρp the density of the particle, f the excitation frequency, εb the dimensionless oscillation magnitude of the bubble, Rb the bubble radius, Rp the particle radius, d the distance between the particle and the bubble, η the viscosity of the ambient fluid, and Us the velocity of the particle relative to the ambient fluid. The motion of micro-objects is determined by competition between Frad and Fdrag. As shown in Eq. (1), Frad acts as the attractive or repulsive force depending on ρf and ρp. On the other hand, objects around the oscillating bubble hover like satellites because of the viscous drag force generated from the streaming flow. Two differently sized micro-objects (i.e., glass beads with diameters of 10 μm and 100 μm) can be separated by using the secondary sound field and the streaming flow generated from an acoustically excited bubble (Fig. 6). When a 300 μm diameter bubble is acoustically agitated by a piezoactuator near its resonant frequency (20 kHz), it attracts large particles (100 μm in diameter) while repelling small particles (10 μm in diameter). The motion of large particles arises from the dominance of Frad over Fdrag. On the contrary, the motion of small particles arises from the dominance of Fdrag over Frad. In this work, Frad corresponds to the attractive force regardless of particle size, because the density of particles we used is larger than that of the ambient fluid (Eq. 2). Similarly, polystyrene particles with 10 μm and 100 μm diameters can also be successfully separated under the same experimental conditions (data not shown). Here, the resonant frequency of the bubble can be experimentally determined by obtaining the maximum amplitude of the oscillating bubble in response to an applied frequency. In addition, it can be theoretically estimated from the following equation: f r (2 )1 (n 1)(n 1)(n 2) / Rb3 , where fr, , and n denote resonant frequency, surface tension, and shape mode (n=8, as illustrated in Fig. 6), respectively.
To validate the on-demand manipulation of biological objects, such as cells or microorganisms in biomedical applications, we showed microparticle micromanipulation by using an 9
optothermally and acoustically actuated bubble, which consists of the abovementioned unit operations. First, a 300 μm-diameter bubble is optothermally generated inside a microfluidic chip by the same process depicted in Fig. 4, and subsequently two different-sized particles (glass beads with 10 μm and 100 μm diameters) are gently dispersed into the ambient fluid [Fig. 7(a)]. When the bubble oscillates under acoustic actuation with 20 kHz resonant frequency, it draws neighboring large particles closer while repelling small particles [Fig. 7(b)]. As mentioned above, particle motions contribute to the attractive and viscous drag forces induced by the secondary sound field and the streaming flow, respectively. As a spot illuminated by a laser beam (300 mW in power) is moved toward a target position, the bubble moves along the illumination path and delivers the captured particles to the target position by using both the secondary radiation and optothermocapillary forces, as shown in Figs. 7(c–d). Finally, when the particles reach the target position, they are unloaded from the bubble by removing the acoustical actuation, as illustrated in Figs. 7(e) and 7(f). We anticipate that our method will be a good alternative or complementary technology to the conventional one and therefore contribute to develop practical applications, such as single-cell manipulation and microdevice assembly.
4. Conclusion We proposed a hybrid handling technique for precise generation of a bubble with target size and for on-demand micromanipulation of micro-objects via the bubble by integrating optothermal and acoustical actuations. We demonstrated that the optothermal scheme is suitable for sizecontrolled creation of bubbles and their easy delivery into a target position. On the other hand, the acoustical scheme enables on-demand sorting, capturing, and releasing of wanted micro-objects based on a secondary acoustic radiation and a streaming flow. Finally, we examined a full-step manipulation process of micro-objects, including generating of a bubble and sorting, capturing, 10
carrying, and releasing of a target micro-object by an optothermally and acoustically activated bubble. To further improve the applicability of our hybrid manipulation technique to biological and biomedical applications, we will develop a high-resolution separation method of a target sample from biological samples (e.g., cells and microorganism) with different shapes and deformabilities.
Acknowledgement This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (20110025039).
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References [1]
C. Yi, C.-W. Li, S. Ji, M. Yang, Microfluidics technology for manipulation and analysis of biological cells, Anal. Chim. Acta 560 (2006) 1-23.
[2]
J. Nilsson, M. Evander, B. Hammarström, T. Laurell, Review of cell and particle trapping in microfluidic systems, Anal. Chim. Acta 649 (2009) 141-157.
[3]
A. Ashkin, Optical trapping and manipulation of neutral particles using lasers, Proc. Natl. Acad. Sci. U. S. A. 94 (1997) 4853-4860.
[4]
D.G. Grier, A revolution in optical manipulation, Nature 424 (2003) 810-816.
[5]
P.Y. Chiou, A.T. Ohta, M.C. Wu, Massively parallel manipulation of single cells and microparticles using optical images, Nature 436 (2005) 370-372.
[6]
A.T. Ohta, P.-Y. Chiou, T.H. Han, J.C. Liao, U. Bhardwaj, E.R.B McCabe, F. Yu, R. Sun, M.C. Wu, Dynamic cell and microparticle control via optoelectronic tweezers, J. Microelectromech. Syst. 16 (2007) 491-499.
[7]
H. Hwang, J.-K. Park, Rapid and selective concentration of microparticles in an optoelectrofluidic platform, Lab Chip 9 (2009) 199-206.
[8]
H.-y. Hsu, A.T. Ohta, P.-Y. Chiou, A. Jamshidi, S.L. Neale, M.C. Wu, Phototransistor-based optoelectronic tweezers for dynamic cell manipulation in cell culture media, Lab Chip 10 (2010) 165-172.
[9]
M.C. Wu, Optoelectronic tweezers, Nat. Photonics 5 (2011) 322-324.
[10]
P.C.H. Li, D.J. Harrison, Transport, manipulation, and reaction of biological cells on-chip using electrokinetic effects, Anal. Chem. 69 (1997) 1564-1568.
[11]
C.R. Cabrera, P. Yager, Continuous concentration of bacteria in a microfluidic flow cell using electrokinetic techniques, Electrophoresis 22 (2001) 355-362.
[12]
P.K. Wong, C.-Y. Chen, T.-H. Wang, C.-M. Ho, Electrokinetic bioprocessor for concentrating 12
cells and molecules, Anal. Chem. 76 (2004) 6908-6914. [13]
J. Voldman, Electrical forces for microscale cell manipulation, Annu. Rev. Biomed. Eng. 8 (2006) 425-454.
[14]
J. Dobson, Remote control of cellular behaviour with magnetic nanoparticles, Nat. Nanotechnol. 3 (2008) 139-143.
[15]
G. Vieira, T. Henighan, A. Chen, A.J. Hauser, F.Y. Yang, J.J. Chalmers, R. Sooryakumar, Magnetic wire traps and programmable manipulation of biological cells, Phys. Rev. Lett. 103 (2009) 128101.
[16]
I. De Vlaminck, C. Dekker, Recent advances in magnetic tweezers, Annu. Rev. Biophys. 41 (2012) 453-472.
[17]
R. Piazza, A. Parola, Thermophoresis in colloidal suspensions, J. Phys. Condens. Matter 20 (2008) 153102.
[18]
H.-R. Jiang, H. Wada, N. Yoshinaga, M. Sano, Manipulation of colloids by a nonequilibrium depletion force in a temperature gradient, Phys. Rev. Lett. 102 (2009) 208301.
[19]
L.H. Thamdrup, N.B. Larsen, A. Kristensen, Light-induced local heating for thermophoretic manipulation of DNA in polymer micro- and nanochannels, Nano lett. 10 (2010) 826-832.
[20]
R.T. Schermer, C.C. Olson, J.P. Coleman, F. Bucholtz, Laser-induced thermophoresis of individual particles in a viscous liquid, Opt. Express 19 (2011) 10571-10586.
[21]
M.R. Reichl, D. Braun, Thermophoretic manipulation of molecules inside living cells, J. Am. Chem. Soc. 136 (2014) 15955-15960.
[22]
A. Nilsson, F. Petersson, H. Jönsson, T. Laurell, Acoustic control of suspended particles in micro fluidic chips, Lab Chip 4 (2004) 131-135.
[23]
T. Laurell, F. Petersson, A. Nilsson, Chip integrated strategies for acoustic separation and manipulation of cells and particles, Chem. Soc. Rev. 36 (2007) 492-506.
[24]
J. Friend, L.Y. Yeo, Microscale acoustofluidics: Microfluidics driven via acoustics and 13
ultrasonics, Rev. Mod. Phys. 83 (2011) 647. [25]
B.R. Lutz, J. Chen, D.T. Schwartz, Hydrodynamic tweezers: 1. Noncontact trapping of single cells using steady streaming microeddies, Anal. Chem. 78 (2006) 5429-5435.
[26]
M. Tanyeri, E.M. Johnson-Chavarria, C.M. Schroeder, Hydrodynamic trap for single particles and cells, Appl. Phys. Lett. 96 (2010) 224101.
[27]
V.H. Lieu, T.A. House, D.T. Schwartz, Hydrodynamic tweezers: Impact of design geometry on flow and microparticle trapping, Anal. Chem. 84 (2012) 1963-1968.
[28]
A. Hashmi, G. Yu, M. Reilly-Collette, G. Heiman, J. Xu, Oscillating bubbles: A versatile tool for lab on a chip applications, Lab Chip 12 (2012) 4216-4227.
[29]
Y. Chen, S. Lee, Manipulation of biological objects using acoustic bubbles: A review, Integr. Comp. Biol. 54 (2014) 959-968.
[30]
C.E. Brennen, Cavitation and bubble dynamics, Cambridge University Press, Cambridge, 2013.
[31]
F.J. Fry, Ultrasound: Its applications in medicine and biology, Elsevier, Amsterdam, 2013.
[32]
S.A. Elder, Cavitation microstreaming, J. Acoust. Soc. Am. 31 (1959) 54-64.
[33]
K. Ryu, S.K. Chung, S.K. Cho, Micropumping by an acoustically excited oscillating bubble for automated implantable microfluidic devices, J. Assoc. Lab. Autom. 15 (2010) 163-171.
[34]
S.K. Chung, Y. Zhao, S.K. Cho, On-chip creation and elimination of microbubbles integrated with EWOD actuations toward micro-object manipulator, J. Micromech. Microeng. 18 (2008) 095009.
[35]
S.K. Chung, S.K. Cho, On-chip manipulation of objects using mobile oscillating bubbles, J. Micromech. Microeng. 18 (2008) 125024.
[36]
S.K. Chung, S.K. Cho, 3-D manipulation of millimeter- and micro-sized objects using an acoustically excited oscillating bubble, Microfluid. Nanofluid. 6 (2009) 261-265.
[37]
J.O. Kwon, J.S. Yang, S.J. Lee, K. Rhee, S.K. Chung, Electromagnetically actuated 14
micromanipulator using an acoustically oscillating bubble, J. Micromech. Microeng. 21 (2011) 115023. [38]
S.K. Chung, J.O. Kwon, S.K. Cho, Manipulation of micro/mini-objects by ACelectrowetting-actuated oscillating bubbles: Capturing, carrying and releasing, J. Adhes. Sci. Technol. 26 (2012) 1965-1983.
[39]
K.H. Lee, J.H. Lee, J.M. Won, K. Rhee, S.K. Chung, Micromanipulation using cavitational microstreaming generated by acoustically oscillating twin bubbles, Sens. Actuator A-Phys. 188 (2012) 442-449.
[40]
J.H. Lee, K.H. Lee, J.B. Chae, K. Rhee, S.K. Chung, On-chip micromanipulation by ACEWOD driven twin bubbles, Sens. Actuator A-Phys. 195 (2013) 167-174.
[41]
J.O. Kwon, J.S. Yang, J.B. Chae, S.K. Chung, Micro-object manipulation in a microfabricated channel using an electromagnetically driven microrobot with an acoustically oscillating bubble, Sens. Actuator A-Phys. 215 (2014) 77-82.
[42]
J.H. Lee, K.H. Lee, J.M. Won, K. Rhee, S.K. Chung, Mobile oscillating bubble actuated by AC-electrowetting-on-dielectric (EWOD) for microfluidic mixing enhancement, Sens. Actuator A-Phys. 182 (2012) 153-162.
[43]
J.M. Won, J.H. Lee, K.H. Lee, K. Rhee, S.K. Chung, Propulsion of water-floating objects by acoustically oscillating microbubbles, Int. J. Precis. Eng. Manuf. 12 (2011) 577-580.
[44]
J.S. Oh, Y.S. Kwon, K.H. Lee, W. Jeong, S.K. Chung, K. Rhee, Drug perfusion enhancement in tissue model by steady streaming induced by oscillating microbubbles, Comput. Biol. Med. 44 (2014) 37-43.
[45]
E. Cho, S.K. Chung, K. Rhee, Streaming flow from ultrasound contrast agents by acoustic waves in a blood vessel model, Ultrasonics 62 (2015) 66-74.
[46]
J.P. Jeon, J. Hong, Y.R. Lee, J.H. Seo, S.H. Oh, S.K. Chung, Manipulation of liquid metal marble for electrical switching application, 18th International Conference on Solid-State 15
Sensors, Actuators and Microsystems (Transducers 2015), Achorage, Alaska, 2015, 18341837 [47]
S.K. Chung, K. Rhee, S.K. Cho, Bubble actuation by electrowetting-on-dielectric (EWOD) and its applications: A review, Int. J. Precis. Eng. Manuf. 11 (2010) 991-1006.
[48]
D. Ahmed, A. Ozcelik, N. Bojanala, N. Nama, A. Upadhyay, Y. Chen, W. Hanna-Rose, T.J. Huang, Rotational manipulation of single cells and organisms using acoustic waves, Nat. Commun. 7 (2016) 11085.
[49]
Y. Chen, Z. Fang, B. Merritt, D. Strack, J. Xu, S. Lee, Onset of particle trapping and release via acoustic bubbles, Lab Chip 16 (2016) 3024-3032.
[50]
J. Feng, J. Yuan, S.K. Cho, 2-D steering and propelling of acoustic bubble-powered microswimmers, Lab Chip 16 (2016) 2317-2325.
[51]
Y. Xie, C. Zhao, Y. Zhao, S. Li, J. Rufo, S. Yang, F. Guo, T.J. Huang, Optoacoustic tweezers: A programmable, localized cell concentrator based on opto-thermally generated, acoustically activated, surface bubbles, Lab Chip 13 (2013) 1772-1779.
[52]
C. Zhao, Y. Xie, Z. Mao, Y. Zhao, J. Rufo, S. Yang, F. Guo, J.D. Mai, T.J. Huang, Theory and experiment on particle trapping and manipulation via optothermally generated bubbles, Lab chip 14 (2014) 384-391.
[53]
Y. Zheng, H. Liu, Y. Wang, C. Zhu, S. Wang, J. Cao, S. Zhu, Accumulating microparticles and direct-writing micropatterns using a continuous-wave laser-induced vapor bubble, Lab Chip 11 (2011) 3816-3820.
[54]
K. Zhang, A. Jian, X. Zhang, Y. Wang, Z. Li, H.-Y. Tam, Laser-induced thermal bubbles for microfluidic applications, Lab Chip 11 (2011) 1389-1395.
[55]
E. Dickinson, R. Ettelaie, B.S. Murray, Z. Du, Kinetics of disproportionation of air bubbles beneath a planar air-water interface stabilized by food proteins, J. Colloid Interface Sci. 252 (2002) 202-213. 16
[56]
M. Kaviany, Essentials of heat transfer: Principles, materials, and applications, Cambridge University Press, Cambridge, 2011.
[57]
P.-G. De Gennes, F. Brochard-Wyart, D. Quéré, Capillarity and wetting phenomena: Drops, bubbles, pearls, waves, Springer Science & Business Media, Berlin, 2013.
[58]
A.T. Ohta, A. Jamshidi, J.K. Valley, H.-Y. Hsu, M.C. Wu, Optically actuated thermocapillary movement of gas bubbles on an absorbing substrate, Appl. Phys. Lett. 91 (2007) 074103.
[59]
W. Hu, K. S. Ishii, A.T. Ohta, Micro-assembly using optically controlled bubble microrobots in saline solution, 2012 IEEE International Conference on Robotics and Automation (ICRA 2012), Saint Paul, Minnesota, 2012, 733-738.
[60]
K.S. Ishii, W. Hu, A.T. Ohta, Cooperative micromanipulation using optically controlled bubble microrobots, 2012 IEEE International Conference on Robotics and Automation (ICRA 2012), Saint Paul, Minnesota, 2012, 3443-3448.
[61]
W. Hu, K.S. Ishii, Q. Fan, A.T. Ohta, Hydrogel microrobots actuated by optically generated vapour bubbles, Lab Chip 12 (2012) 3821-3826.
[62]
W. Hu, Q. Fan, A.T. Ohta, An opto-thermocapillary cell micromanipulator, Lab Chip 13 (2013) 2285-2291.
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Biographies Jae Hun Shin received the Bachelor’s degree of mechanical engineering from Myongji University in 2013. He currently is a graduate student in Myongji University and his research interests lie on MEMS and Microfluidics applications.
Jeonghwa Seo received the Bachelor’s degree of mechanical engineering from Myongji University in 2016. He currently is a graduate student in Myongji University and his research interests lie on the development of microfluidic applications for on-chip micromanipulation, and magnetically driven liquid metal manipulation.
Jiwoo Hong received his BS and MS degrees in Chemical Engineering from Sogang University (Seoul, Korea) and POSTECH (Pohang, Korea) in 2005 and 2007, respectively. He also received Ph. D. degree from Department of Mechanical Engineering of POSTECH in 2014. Currently, he is working as a research professor at the same university. His research interests include electrowetting and electrohydrodynamics.
Sang Kug Chung Sang Kug Chung is an associate professor of the department of mechanical engineering at the Myongji University in Korea. He received the Ph.D. degree in Mechanical Engineering and Materials Science from the University of Pittsburgh in 2009 along with the Graduate Research Excellence Award. He received the M.S. degree from Pohang University of 18
Science and Technology (POSTECH) and B.S. from Myongji University. He had worked for the development of the world first Liquid Lens at Samsung Electro-Mechanics from 2003 to 2009. Upon joining the faculty at Myongji University in 2009, he has directed the Microsystems Laboratory. And he has also served as a principal investigator in the Advanced Microfluids Engineering Research Laboratory (AMERL) since 2013. His research is in microfluidics and MEMS, including design and fabrication of micro/nano actuators and systems.
Figure Captions Fig. 1 Schematic diagram of manipulation of microparticles with two different sizes by utilizing an optothermally and acoustically excited bubble on demand. (a) Dispersed microparticles with different sizes. (b) Generation of a bubble through optothermal effects. (c) Transportation of the bubble toward the dispersed microparticles by using optothermocapillary effects. (d) Sorting and capturing of target particles with a specific size by means of acoustic radiation effects. (e) Transportation of captured particles through both optothermocapillary and acoustic radiation effects. (f) Releasing captured particles in the absence of acoustic agitation and subsequent return to the original position by way of optothermocapillary effects.
Fig. 2 Schematic of the fabrication procedures of a microfluidic chip for micromanipulation of micro-objects.
Fig. 3 Schematic diagram of the overall experimental setup for micromanipulation of mico-objects via an optothermally and acoustically excited bubble.
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Fig. 4 Size variation of optothermally-generated bubbles as a function of illumination time of laser beams with different powers. The insets illustrate sequential snapshots of bubble generation and growth.
Fig. 5 Optothermocapillary-driven bubble transportation. (a) An optothermally-generated bubble in an aqueous medium. (b–c) When a bubble is illuminated by a focused laser beam (532 nm wavelength and 300 mW power), it is stably trapped above the locally illuminated spot, and subsequently it follows along the movement of the laser beam. (d) When the laser beam is turned off, the bubble is released at the target position. Fig. 6 Capturing and repelling of micro-objects with different sizes (glass beads with 10 and 100 μm diameter) near an acoustically agitated bubble (300 μm in diameter). (a) When a bubble is acoustically agitated, it attracts large glass beads with 100 μm diameter. (b) Under the same acoustic agitation, the bubble repels small glass beads with 10 μm diameter. Here, the subscripts denote the time sequence of the capturing and repelling processes.
Fig. 7 Micromanipulation of micro-objects via a bubble based on acoustic radiation and optothermocapillary effects. (a) An optothermally generated bubble in an aqueous medium, containing particles with different sizes (glass beads with 10 μm and 100 μm diameter). (b) Sorting and capturing of particles by using acoustic radiation forces generated from an acoustically agitated bubble. (c) Transporting of captured particles (glass beads with 100 μm diameter) by using acoustic radiation and optothermocapillary forces simultaneously. (d–f) Releasing of carried particles without laser beam illumination and acoustic agitation.
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Fig. 1 Schematic diagram of manipulation of microparticles with two different sizes by utilizing an optothermally and acoustically excited bubble on demand. (a) Dispersed microparticles with different sizes. (b) Generation of a bubble through optothermal effects. (c) Transportation of the bubble toward the dispersed microparticles by using optothermocapillary effects. (d) Sorting and capturing of target particles with a specific size by means of acoustic radiation effects. (e) Transportation of captured particles through both optothermocapillary and acoustic radiation effects. (f) Releasing captured particles in the absence of acoustic agitation and subsequent return to the original position by way of optothermocapillary effects.
Fig. 2 Schematic of the fabrication procedures of a microfluidic chip for micromanipulation of micro-objects.
21
Fig. 3 Schematic diagram of the overall experimental setup for micromanipulation of mico-objects via an optothermally and acoustically excited bubble.
Fig. 4 Size variation of optothermally-generated bubbles as a function of illumination time of laser beams with different powers. The insets illustrate sequential snapshots of bubble generation and growth.
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Fig. 5 Optothermocapillary-driven bubble transportation. (a) An optothermally-generated bubble in an aqueous medium. (b–c) When a bubble is illuminated by a focused laser beam (532 nm wavelength and 300 mW power), it is stably trapped above the locally illuminated spot, and subsequently it follows along the movement of the laser beam. (d) When the laser beam is turned off, the bubble is released at the target position.
Fig. 6 Capturing and repelling of micro-objects with different sizes (glass beads with 10 and 100 μm diameter) near an acoustically agitated bubble (300 μm in diameter). (a) When a bubble is acoustically agitated, it attracts large glass beads with 100 μm diameter. (b) Under the same acoustic agitation, the bubble repels small glass beads with 10 μm diameter. Here, the subscripts denote the time sequence of the capturing and repelling processes.
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Fig. 7 Micromanipulation of micro-objects via a bubble based on acoustic radiation and optothermocapillary effects. (a) An optothermally generated bubble in an aqueous medium, containing particles with different sizes (glass beads with 10 μm and 100 μm diameter). (b) Sorting and capturing of particles by using acoustic radiation forces generated from an acoustically agitated bubble. (c) Transporting of captured particles (glass beads with 100 μm diameter) by using acoustic radiation and optothermocapillary forces simultaneously. (d–f) Releasing of carried particles without laser beam illumination and acoustic agitation.
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S0925-4005(17)30269-1 http://dx.doi.org/doi:10.1016/j.snb.2017.02.049 SNB 21780
To appear in:
Sensors and Actuators B
Received date: Revised date: Accepted date:
12-12-2016 3-2-2017 9-2-2017
Please cite this article as: Jae Hun Shin, Jeonghwa Seo, Jiwoo Hong, Sang Kug Chung, Hybrid optothermal and acoustic manipulations of microbubbles for precise and on-demand handling of micro-objects, Sensors and Actuators B: Chemical http://dx.doi.org/10.1016/j.snb.2017.02.049 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Hybrid optothermal and acoustic manipulations of microbubbles for precise and on-demand handling of micro-objects Jae Hun Shin†1, Jeonghwa Seo†1, Jiwoo Hong2*, Sang Kug Chung1* 1
Department of Mechanical Engineering, Myongji University, Yongin, Gyeonggido, South Korea
2
Department of Mechanical Engineering, Pohang University of Science and Technology
(POSTECH), San 31, Hyoja-dong, Pohang 790-784, South Korea
Co-corresponding Authors *
Phone: +82-31-330-6346. Fax: +82-31-330-6957. E-mail: [email protected].
*
Phone: +82-54-279-8201. Fax: +82-54-279-5899. E-mail: [email protected].
†These authors contributed equally to this work. 1
Graphical abstract
Research Highlights
For precise and on-demand handling of micro-objects, we propose the integrated strategy combining strengths of optothermal and acoustical handling strategies.
Microbubbles can be optothermally generated, and their size can be tuned by controlling the illumination time and power of a laser beam.
The bubbles can be delivered into a preferred position through optothermocapillary flow.
Micro-objects with two different sizes can be selectively separated, and then only a micro-object with a specific size can be collected through a secondary acoustic radiation and a streaming flow generated from an acoustically oscillating bubble.
Abstract Manipulating specific micro-objects (e.g., colloidal particles and microorganisms) precisely and selectively in liquid medium is of great importance in myriad engineering fields. We here develop a hybrid technique for micromanipulation of micro-objects by incorporating optothermally and acoustically excited bubble on-demand. The integrated strategy combines strengths of optothermal (e.g., precise size control in bubble creation and easy delivery of micro-objects into target position) and acoustical (e.g., on-demand capturing and precise sorting of micro-objects) strategies. Microbubbles can be optothermally generated, and their size can be regulated by tuning the illumination time and power of a laser beam. The bubbles can be delivered into a preferred position 2
through optothermocapillary flow. Sequentially, micro-objects with two different sizes can be selectively separated, and then only a micro-object with a specific size can be collected through a secondary acoustic radiation and a streaming flow generated from an acoustically oscillating bubble. To emulate on-demand manipulation of bio-objects in technological applications, we examine a fullstep manipulation process of micro-objects, which consists of generating bubbles and sorting/capturing/carrying/releasing of desired micro-objects under optothermal and acoustical actuations. The hybrid manipulation technique can be a good alternative technology to conventional ones and thus can be utilized in biological applications and micro-device assembly. Keywords: Micromanipulation of micro-objects; Bubble oscillation; Secondary acoustic radiation; Microstreaming flow; Optothermocapillary flow
1. Introduction The precise and on-demand handling (e.g., trapping/releasing, sorting, and carrying) of micro-objects (e.g., colloidal particles, cells, and microorganisms) in liquid medium is mightily important in various fields of academic research and engineering applications, such as biology, chemistry, physics, materials, and medicine [1,2]. Diverse techniques for handling micro-objects have been proposed based on optical [3-5] (or optoelectronical [6-9]), electrical [10-13], magnetic [14-16], mechanical [14-16], thermal [17-21], and acoustic [22-24] and hydrodynamic [25-27] forces. Among such existing techniques, an acoustic field-based technique, especially a bubble-mediated acoustical actuation, has shown potential as an effective handling strategy for microfluidic and biofluidic applications [28,29]. Bubble-mediated technique can manipulate samples, such as cells and microorganisms, without any unwanted damage caused by electric or magnetic fields and without cross-contamination caused by direct contact between the manipulator and samples [29]. When a bubble oscillates under the action of an acoustic field, it autonomously radiates a secondary sound field and simultaneously generate a streaming flow around it [29-32]. Accordingly, neighbouring objects around the bubbles experience two forces—secondary radiation force (Frad) 3
caused by the secondary sound field and drag force (Fdrag) caused by the streaming flow [29-32]. As a result, the motion of the objects is determined by a competition between Frad and Fdrag, and it is affected by physical parameters, such as bubble and object sizes, frequency of acoustic excitations, and densities of objects and liquid medium [28,29]. The competition between the two forces and the resulting motion of objects will be explained in detail in the Results and discussion section. On the basis of the remarkable features of an oscillating bubble, many researchers have developed a myriad of microfluidic devices, including fluidic regulators (e.g., micropump and micromixer) and micro-object manipulator (e.g., filter, transporter, microrotor, and micropropeller), as well as biological (or biomedical) applications (e.g., cell lysis, and drug and gene delivery) [28,29]. We have also developed oscillating bubble-based microfluidic components (e.g., micropump [33], manipulator [34-41], micromixer [42] and micromotor [43]), biomedical applications (e.g., drug delivery [44] and ultrasound contrast agents [45]), and energy harvesting system [46]. The bubble oscillation-based microfluidic applications were well summarized in review papers [28,29,47] and recently published papers [48-50]. In spite of these considerable efforts, technological limitations still exist on precision and ondemand control over the size and position of the generated bubble. To solve those, Xie et al. [51] first demonstrated dynamic control of optothermal bubble generation by tuning the power and position of a laser focused on a gold film and subsequently trapped the cells through acoustic radiation forces by applying acoustic waves. Their proposed method (called as optoacoustic tweezers) has many advantages such as programmable and biocompatible cell manipulation, and easy integration into microfluidic units. Furthermore, they showed bubble generation and particle manipulation (e.g., trapping and carrying) via the bubble by only incorporating optothermal effects [52]. Nevertheless, their techniques can still be developed. For instance, the development of a fully integrated technique that combines strengths of acoustic and optothermal manipulation is required for further precise and on-demand handling of samples. 4
Thus, we here propose a hybrid microbubble-based manipulation technique for precise and on-demand handling of micro-objects by synergistically combining optothermal and acoustical strategies. The optothermal strategy allows for precise control over the size of the generated bubble, as well as facile transportation of the bubble. On the other hand, the acoustical strategy enables the capture (or release) and separation of samples on-demand. Figure 1 illustrates the schematic diagram of micromanipulation of micro-objects by utilizing optothermally and acoustically excited bubble. When a laser beam is focused onto the bottom substrate covered with an amorphous silicon layer of microfluidic chip, the generation and growth of a microbubble on the illustrated spot occurs due to optothermal effects [Figs. 1(a) and 1(b)]. The bubble can be transported toward near the microparticles with two different sizes by controlling the laser beam due to optothermocapillary effects [Fig. 1(c)]. When the bubble oscillates around its resonant frequency under an acoustical excitation, it can attract large microparticles while can repulse small ones due to competition between acoustic radiation and drag forces [Fig. 1(d)]. The bubble loaded with large microparticles can be transported to a preferred position under both optothermal and acoustical actuations [Fig. 1(e)]. After the bubble arrives at the chosen position, it can release large microparticles by ceasing an acoustic actuation, and subsequently, it can return to its original position by optothermocapillary effects [Fig. 1(f)]. The principle of each operation that involves the proposed on-chip manipulation will be explained thoroughly in the Results and discussion section.
2. Experimental details To demonstrate micromanipulation of micro-objects by utilizing an optothermally and acoustically excited bubble, a microfluidic chip consisting of top and bottom glass plates was fabricated by the following procedure. First, an amorphous silicon layer with 500 nm thickness was deposited onto the bottom glass plate (75 mm in length × 25 mm in width) by low-pressure deposition of chemical vapor, as illustrated in Figs. 2(a) and 2(b). Subsequently, the top and bottom 5
plates were treated by cleaning system of ultraviolet ozone (Jelight Company Inc., USA) to produce hydrophilic surfaces, thereby minimizing the contact area between the bubble and the plates [Figs. 2(c)–(e)]. Finally, a small amount of water was poured into an acrylic chamber (7.5 cm in length × 2.5 cm in width × 0.5 cm in height), and subsequently, the top plate was gently placed on top of the bottom plate, separated by a spacer with 250 μm in height at the end edges [Fig. 2(f)].
Figure 3 illustrates schematic diagram of the overall experimental setup for manipulation of objects in the fabricated microfluidic chip. For optothermally-induced generation of a microbubble, the Nd: YAG laser beam with 532 nm wavelength (Changchun New Industries Optoelectronics Tech. Co., China) was guided through a plane mirror (Nd: YAG laser line mirror, Edmund Optics, USA) and was focused onto an amorphous silicon layer of the bottom plate. Here, the focused laser beam has a diameter of about 500 μm. For the movement of the generated microbubble by optothermocapillary effects, a 2D motorized translation stage (Edmund Optics, USA) was used to change the position of laser beam irradiation. For a manipulation of micro-objects via an acoustically-agitated microbubble, AC electrical signals, produced by a function generator (33210A, Agilent Co., USA) and then amplified (BA4825, NF Co., Japan), were applied to a piezoactuator (PIC151, Physik Instruments Inc., Germany) attached to the side wall of the acrylic chamber. The dynamic behavior of a bubble and micro-objects (glass beads with a 10 and 100 μm diameter; Sigma, USA) was sequentially recorded by using a charge-coupled device camera (EO-1312C, Edmund Optics, USA) and a high-speed camera (Phantom Miro eX2, Vision Research, USA). Every experiment was repeated at least five times, and the data presented in the Results and discussion section are the average of the results.
6
3. Results and discussion When a laser beam (532 nm wavelength) generated from a Nd: YAG laser is focused onto an amorphous silicon layer (500 nm in thickness), which acts as a light absorber, deposited on the bottom plate, a microbubble is generated and gradually expanded by optothermal effect. Figure 4 illustrates the temporal variation in the size of optothermally-generated bubbles during irradiation of laser beams with different powers of 500, 600, and 700 mW. We can reproducibly generate bubbles with diameters that range from 260 μm to 840 μm. After sudden birth of a microbubble with specific size, the size of the generated microbubble is almost linearly proportional to the illumination time of a laser beam and is increased by the laser power. When a laser power is larger than certain threshold value (500 mW in the present work), the water on the focusing spot of laser beam reaches its boiling point and resultantly a microbubble is generated. Subsequently, the bubble thermally grows and its size increases almost linearly with the illumination time. This tendency is similar to that reported by previous studies [51, 53, 54]. In addition, the generated bubble stably stays on the amorphous silicon layer during its expansion. These results are similar to those reported in previous works [51, 52]. Different from those works, however, sudden shrinkage of the bubble after turning off the laser power is hardly observed, which may result from the following reasons: First, bubble shrinkage is due to gas diffusion from the bubble, which accelerates as the bubble becomes smaller [55]. The size of an optothermally-generated bubble reported in previous works is considerably smaller than that observed in the present work. Second, an amorphous silicon layer as a light absorber used in the present work has a lower thermal conductivity than the gold film used in previous works [56]. Accordingly, its temperature does not suddenly decrease, thereby maintaining its size stably even though the laser power is turned off. Consequently, we can precisely control the size of the generated bubble by tuning the illumination time and power of the laser beam, and stably manipulate the bubble.
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The optothermally-generated bubble can be transported toward a target position by using optothermocapillary effects, as shown in Fig. 5. A bubble with 300 μm diameter is preferentially generated by illuminating a laser beam with 600 mW power onto the light absorbing substrate, as shown in Fig. 4. When a 300 mW power laser beam is focused onto the region in the vicinity of the bubble, the optically-induced heating of the absorbing substrate generates a thermal gradient around the bubble. The temperature gradient creates a gradient of surface tension, which drives a fluid flow from heating to non-heating regions [57]. As a result, the bubble moves toward the optical heating region. This phenomenon is called optothermocapillary effect [58-62]. When the position of a laser beam is moved by a motorized, the bubble follows the position of the laser spot. On the other hand, when the laser power is turned off, the bubble is released at the target position. Note that, compared with the power (600 mW) used to generate a bubble, a lower power of the laser (300 mW) was employed to transport a bubble, thereby minimizing the unwanted change of bubble volume by bubble expansion or any damage of a microchip. As mentioned in the Introduction, it is well-known phenomenon that when a bubble oscillates through acoustic excitation, it radiates a secondary sound field and simultaneously generates a streaming flow around it. Therefore, micro-objects around the oscillating bubble undergo a secondary radiation force (attractive or repulsive force) by the radiated sound field and a drag force by the streaming flow. For an oscillating bubble and a rigid spherical particle, the secondary radiation force (Frad) and viscous drag force (Fdrag) are estimated by the following equations:
f p f 2 b 2 Rb 6 Rp3 Frad 4f 2 d5 p f
(1)
Fdrag 6 RpUs
(2)
8
where ρf is the density of the ambient fluid, ρp the density of the particle, f the excitation frequency, εb the dimensionless oscillation magnitude of the bubble, Rb the bubble radius, Rp the particle radius, d the distance between the particle and the bubble, η the viscosity of the ambient fluid, and Us the velocity of the particle relative to the ambient fluid. The motion of micro-objects is determined by competition between Frad and Fdrag. As shown in Eq. (1), Frad acts as the attractive or repulsive force depending on ρf and ρp. On the other hand, objects around the oscillating bubble hover like satellites because of the viscous drag force generated from the streaming flow. Two differently sized micro-objects (i.e., glass beads with diameters of 10 μm and 100 μm) can be separated by using the secondary sound field and the streaming flow generated from an acoustically excited bubble (Fig. 6). When a 300 μm diameter bubble is acoustically agitated by a piezoactuator near its resonant frequency (20 kHz), it attracts large particles (100 μm in diameter) while repelling small particles (10 μm in diameter). The motion of large particles arises from the dominance of Frad over Fdrag. On the contrary, the motion of small particles arises from the dominance of Fdrag over Frad. In this work, Frad corresponds to the attractive force regardless of particle size, because the density of particles we used is larger than that of the ambient fluid (Eq. 2). Similarly, polystyrene particles with 10 μm and 100 μm diameters can also be successfully separated under the same experimental conditions (data not shown). Here, the resonant frequency of the bubble can be experimentally determined by obtaining the maximum amplitude of the oscillating bubble in response to an applied frequency. In addition, it can be theoretically estimated from the following equation: f r (2 )1 (n 1)(n 1)(n 2) / Rb3 , where fr, , and n denote resonant frequency, surface tension, and shape mode (n=8, as illustrated in Fig. 6), respectively.
To validate the on-demand manipulation of biological objects, such as cells or microorganisms in biomedical applications, we showed microparticle micromanipulation by using an 9
optothermally and acoustically actuated bubble, which consists of the abovementioned unit operations. First, a 300 μm-diameter bubble is optothermally generated inside a microfluidic chip by the same process depicted in Fig. 4, and subsequently two different-sized particles (glass beads with 10 μm and 100 μm diameters) are gently dispersed into the ambient fluid [Fig. 7(a)]. When the bubble oscillates under acoustic actuation with 20 kHz resonant frequency, it draws neighboring large particles closer while repelling small particles [Fig. 7(b)]. As mentioned above, particle motions contribute to the attractive and viscous drag forces induced by the secondary sound field and the streaming flow, respectively. As a spot illuminated by a laser beam (300 mW in power) is moved toward a target position, the bubble moves along the illumination path and delivers the captured particles to the target position by using both the secondary radiation and optothermocapillary forces, as shown in Figs. 7(c–d). Finally, when the particles reach the target position, they are unloaded from the bubble by removing the acoustical actuation, as illustrated in Figs. 7(e) and 7(f). We anticipate that our method will be a good alternative or complementary technology to the conventional one and therefore contribute to develop practical applications, such as single-cell manipulation and microdevice assembly.
4. Conclusion We proposed a hybrid handling technique for precise generation of a bubble with target size and for on-demand micromanipulation of micro-objects via the bubble by integrating optothermal and acoustical actuations. We demonstrated that the optothermal scheme is suitable for sizecontrolled creation of bubbles and their easy delivery into a target position. On the other hand, the acoustical scheme enables on-demand sorting, capturing, and releasing of wanted micro-objects based on a secondary acoustic radiation and a streaming flow. Finally, we examined a full-step manipulation process of micro-objects, including generating of a bubble and sorting, capturing, 10
carrying, and releasing of a target micro-object by an optothermally and acoustically activated bubble. To further improve the applicability of our hybrid manipulation technique to biological and biomedical applications, we will develop a high-resolution separation method of a target sample from biological samples (e.g., cells and microorganism) with different shapes and deformabilities.
Acknowledgement This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (20110025039).
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References [1]
C. Yi, C.-W. Li, S. Ji, M. Yang, Microfluidics technology for manipulation and analysis of biological cells, Anal. Chim. Acta 560 (2006) 1-23.
[2]
J. Nilsson, M. Evander, B. Hammarström, T. Laurell, Review of cell and particle trapping in microfluidic systems, Anal. Chim. Acta 649 (2009) 141-157.
[3]
A. Ashkin, Optical trapping and manipulation of neutral particles using lasers, Proc. Natl. Acad. Sci. U. S. A. 94 (1997) 4853-4860.
[4]
D.G. Grier, A revolution in optical manipulation, Nature 424 (2003) 810-816.
[5]
P.Y. Chiou, A.T. Ohta, M.C. Wu, Massively parallel manipulation of single cells and microparticles using optical images, Nature 436 (2005) 370-372.
[6]
A.T. Ohta, P.-Y. Chiou, T.H. Han, J.C. Liao, U. Bhardwaj, E.R.B McCabe, F. Yu, R. Sun, M.C. Wu, Dynamic cell and microparticle control via optoelectronic tweezers, J. Microelectromech. Syst. 16 (2007) 491-499.
[7]
H. Hwang, J.-K. Park, Rapid and selective concentration of microparticles in an optoelectrofluidic platform, Lab Chip 9 (2009) 199-206.
[8]
H.-y. Hsu, A.T. Ohta, P.-Y. Chiou, A. Jamshidi, S.L. Neale, M.C. Wu, Phototransistor-based optoelectronic tweezers for dynamic cell manipulation in cell culture media, Lab Chip 10 (2010) 165-172.
[9]
M.C. Wu, Optoelectronic tweezers, Nat. Photonics 5 (2011) 322-324.
[10]
P.C.H. Li, D.J. Harrison, Transport, manipulation, and reaction of biological cells on-chip using electrokinetic effects, Anal. Chem. 69 (1997) 1564-1568.
[11]
C.R. Cabrera, P. Yager, Continuous concentration of bacteria in a microfluidic flow cell using electrokinetic techniques, Electrophoresis 22 (2001) 355-362.
[12]
P.K. Wong, C.-Y. Chen, T.-H. Wang, C.-M. Ho, Electrokinetic bioprocessor for concentrating 12
cells and molecules, Anal. Chem. 76 (2004) 6908-6914. [13]
J. Voldman, Electrical forces for microscale cell manipulation, Annu. Rev. Biomed. Eng. 8 (2006) 425-454.
[14]
J. Dobson, Remote control of cellular behaviour with magnetic nanoparticles, Nat. Nanotechnol. 3 (2008) 139-143.
[15]
G. Vieira, T. Henighan, A. Chen, A.J. Hauser, F.Y. Yang, J.J. Chalmers, R. Sooryakumar, Magnetic wire traps and programmable manipulation of biological cells, Phys. Rev. Lett. 103 (2009) 128101.
[16]
I. De Vlaminck, C. Dekker, Recent advances in magnetic tweezers, Annu. Rev. Biophys. 41 (2012) 453-472.
[17]
R. Piazza, A. Parola, Thermophoresis in colloidal suspensions, J. Phys. Condens. Matter 20 (2008) 153102.
[18]
H.-R. Jiang, H. Wada, N. Yoshinaga, M. Sano, Manipulation of colloids by a nonequilibrium depletion force in a temperature gradient, Phys. Rev. Lett. 102 (2009) 208301.
[19]
L.H. Thamdrup, N.B. Larsen, A. Kristensen, Light-induced local heating for thermophoretic manipulation of DNA in polymer micro- and nanochannels, Nano lett. 10 (2010) 826-832.
[20]
R.T. Schermer, C.C. Olson, J.P. Coleman, F. Bucholtz, Laser-induced thermophoresis of individual particles in a viscous liquid, Opt. Express 19 (2011) 10571-10586.
[21]
M.R. Reichl, D. Braun, Thermophoretic manipulation of molecules inside living cells, J. Am. Chem. Soc. 136 (2014) 15955-15960.
[22]
A. Nilsson, F. Petersson, H. Jönsson, T. Laurell, Acoustic control of suspended particles in micro fluidic chips, Lab Chip 4 (2004) 131-135.
[23]
T. Laurell, F. Petersson, A. Nilsson, Chip integrated strategies for acoustic separation and manipulation of cells and particles, Chem. Soc. Rev. 36 (2007) 492-506.
[24]
J. Friend, L.Y. Yeo, Microscale acoustofluidics: Microfluidics driven via acoustics and 13
ultrasonics, Rev. Mod. Phys. 83 (2011) 647. [25]
B.R. Lutz, J. Chen, D.T. Schwartz, Hydrodynamic tweezers: 1. Noncontact trapping of single cells using steady streaming microeddies, Anal. Chem. 78 (2006) 5429-5435.
[26]
M. Tanyeri, E.M. Johnson-Chavarria, C.M. Schroeder, Hydrodynamic trap for single particles and cells, Appl. Phys. Lett. 96 (2010) 224101.
[27]
V.H. Lieu, T.A. House, D.T. Schwartz, Hydrodynamic tweezers: Impact of design geometry on flow and microparticle trapping, Anal. Chem. 84 (2012) 1963-1968.
[28]
A. Hashmi, G. Yu, M. Reilly-Collette, G. Heiman, J. Xu, Oscillating bubbles: A versatile tool for lab on a chip applications, Lab Chip 12 (2012) 4216-4227.
[29]
Y. Chen, S. Lee, Manipulation of biological objects using acoustic bubbles: A review, Integr. Comp. Biol. 54 (2014) 959-968.
[30]
C.E. Brennen, Cavitation and bubble dynamics, Cambridge University Press, Cambridge, 2013.
[31]
F.J. Fry, Ultrasound: Its applications in medicine and biology, Elsevier, Amsterdam, 2013.
[32]
S.A. Elder, Cavitation microstreaming, J. Acoust. Soc. Am. 31 (1959) 54-64.
[33]
K. Ryu, S.K. Chung, S.K. Cho, Micropumping by an acoustically excited oscillating bubble for automated implantable microfluidic devices, J. Assoc. Lab. Autom. 15 (2010) 163-171.
[34]
S.K. Chung, Y. Zhao, S.K. Cho, On-chip creation and elimination of microbubbles integrated with EWOD actuations toward micro-object manipulator, J. Micromech. Microeng. 18 (2008) 095009.
[35]
S.K. Chung, S.K. Cho, On-chip manipulation of objects using mobile oscillating bubbles, J. Micromech. Microeng. 18 (2008) 125024.
[36]
S.K. Chung, S.K. Cho, 3-D manipulation of millimeter- and micro-sized objects using an acoustically excited oscillating bubble, Microfluid. Nanofluid. 6 (2009) 261-265.
[37]
J.O. Kwon, J.S. Yang, S.J. Lee, K. Rhee, S.K. Chung, Electromagnetically actuated 14
micromanipulator using an acoustically oscillating bubble, J. Micromech. Microeng. 21 (2011) 115023. [38]
S.K. Chung, J.O. Kwon, S.K. Cho, Manipulation of micro/mini-objects by ACelectrowetting-actuated oscillating bubbles: Capturing, carrying and releasing, J. Adhes. Sci. Technol. 26 (2012) 1965-1983.
[39]
K.H. Lee, J.H. Lee, J.M. Won, K. Rhee, S.K. Chung, Micromanipulation using cavitational microstreaming generated by acoustically oscillating twin bubbles, Sens. Actuator A-Phys. 188 (2012) 442-449.
[40]
J.H. Lee, K.H. Lee, J.B. Chae, K. Rhee, S.K. Chung, On-chip micromanipulation by ACEWOD driven twin bubbles, Sens. Actuator A-Phys. 195 (2013) 167-174.
[41]
J.O. Kwon, J.S. Yang, J.B. Chae, S.K. Chung, Micro-object manipulation in a microfabricated channel using an electromagnetically driven microrobot with an acoustically oscillating bubble, Sens. Actuator A-Phys. 215 (2014) 77-82.
[42]
J.H. Lee, K.H. Lee, J.M. Won, K. Rhee, S.K. Chung, Mobile oscillating bubble actuated by AC-electrowetting-on-dielectric (EWOD) for microfluidic mixing enhancement, Sens. Actuator A-Phys. 182 (2012) 153-162.
[43]
J.M. Won, J.H. Lee, K.H. Lee, K. Rhee, S.K. Chung, Propulsion of water-floating objects by acoustically oscillating microbubbles, Int. J. Precis. Eng. Manuf. 12 (2011) 577-580.
[44]
J.S. Oh, Y.S. Kwon, K.H. Lee, W. Jeong, S.K. Chung, K. Rhee, Drug perfusion enhancement in tissue model by steady streaming induced by oscillating microbubbles, Comput. Biol. Med. 44 (2014) 37-43.
[45]
E. Cho, S.K. Chung, K. Rhee, Streaming flow from ultrasound contrast agents by acoustic waves in a blood vessel model, Ultrasonics 62 (2015) 66-74.
[46]
J.P. Jeon, J. Hong, Y.R. Lee, J.H. Seo, S.H. Oh, S.K. Chung, Manipulation of liquid metal marble for electrical switching application, 18th International Conference on Solid-State 15
Sensors, Actuators and Microsystems (Transducers 2015), Achorage, Alaska, 2015, 18341837 [47]
S.K. Chung, K. Rhee, S.K. Cho, Bubble actuation by electrowetting-on-dielectric (EWOD) and its applications: A review, Int. J. Precis. Eng. Manuf. 11 (2010) 991-1006.
[48]
D. Ahmed, A. Ozcelik, N. Bojanala, N. Nama, A. Upadhyay, Y. Chen, W. Hanna-Rose, T.J. Huang, Rotational manipulation of single cells and organisms using acoustic waves, Nat. Commun. 7 (2016) 11085.
[49]
Y. Chen, Z. Fang, B. Merritt, D. Strack, J. Xu, S. Lee, Onset of particle trapping and release via acoustic bubbles, Lab Chip 16 (2016) 3024-3032.
[50]
J. Feng, J. Yuan, S.K. Cho, 2-D steering and propelling of acoustic bubble-powered microswimmers, Lab Chip 16 (2016) 2317-2325.
[51]
Y. Xie, C. Zhao, Y. Zhao, S. Li, J. Rufo, S. Yang, F. Guo, T.J. Huang, Optoacoustic tweezers: A programmable, localized cell concentrator based on opto-thermally generated, acoustically activated, surface bubbles, Lab Chip 13 (2013) 1772-1779.
[52]
C. Zhao, Y. Xie, Z. Mao, Y. Zhao, J. Rufo, S. Yang, F. Guo, J.D. Mai, T.J. Huang, Theory and experiment on particle trapping and manipulation via optothermally generated bubbles, Lab chip 14 (2014) 384-391.
[53]
Y. Zheng, H. Liu, Y. Wang, C. Zhu, S. Wang, J. Cao, S. Zhu, Accumulating microparticles and direct-writing micropatterns using a continuous-wave laser-induced vapor bubble, Lab Chip 11 (2011) 3816-3820.
[54]
K. Zhang, A. Jian, X. Zhang, Y. Wang, Z. Li, H.-Y. Tam, Laser-induced thermal bubbles for microfluidic applications, Lab Chip 11 (2011) 1389-1395.
[55]
E. Dickinson, R. Ettelaie, B.S. Murray, Z. Du, Kinetics of disproportionation of air bubbles beneath a planar air-water interface stabilized by food proteins, J. Colloid Interface Sci. 252 (2002) 202-213. 16
[56]
M. Kaviany, Essentials of heat transfer: Principles, materials, and applications, Cambridge University Press, Cambridge, 2011.
[57]
P.-G. De Gennes, F. Brochard-Wyart, D. Quéré, Capillarity and wetting phenomena: Drops, bubbles, pearls, waves, Springer Science & Business Media, Berlin, 2013.
[58]
A.T. Ohta, A. Jamshidi, J.K. Valley, H.-Y. Hsu, M.C. Wu, Optically actuated thermocapillary movement of gas bubbles on an absorbing substrate, Appl. Phys. Lett. 91 (2007) 074103.
[59]
W. Hu, K. S. Ishii, A.T. Ohta, Micro-assembly using optically controlled bubble microrobots in saline solution, 2012 IEEE International Conference on Robotics and Automation (ICRA 2012), Saint Paul, Minnesota, 2012, 733-738.
[60]
K.S. Ishii, W. Hu, A.T. Ohta, Cooperative micromanipulation using optically controlled bubble microrobots, 2012 IEEE International Conference on Robotics and Automation (ICRA 2012), Saint Paul, Minnesota, 2012, 3443-3448.
[61]
W. Hu, K.S. Ishii, Q. Fan, A.T. Ohta, Hydrogel microrobots actuated by optically generated vapour bubbles, Lab Chip 12 (2012) 3821-3826.
[62]
W. Hu, Q. Fan, A.T. Ohta, An opto-thermocapillary cell micromanipulator, Lab Chip 13 (2013) 2285-2291.
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Biographies Jae Hun Shin received the Bachelor’s degree of mechanical engineering from Myongji University in 2013. He currently is a graduate student in Myongji University and his research interests lie on MEMS and Microfluidics applications.
Jeonghwa Seo received the Bachelor’s degree of mechanical engineering from Myongji University in 2016. He currently is a graduate student in Myongji University and his research interests lie on the development of microfluidic applications for on-chip micromanipulation, and magnetically driven liquid metal manipulation.
Jiwoo Hong received his BS and MS degrees in Chemical Engineering from Sogang University (Seoul, Korea) and POSTECH (Pohang, Korea) in 2005 and 2007, respectively. He also received Ph. D. degree from Department of Mechanical Engineering of POSTECH in 2014. Currently, he is working as a research professor at the same university. His research interests include electrowetting and electrohydrodynamics.
Sang Kug Chung Sang Kug Chung is an associate professor of the department of mechanical engineering at the Myongji University in Korea. He received the Ph.D. degree in Mechanical Engineering and Materials Science from the University of Pittsburgh in 2009 along with the Graduate Research Excellence Award. He received the M.S. degree from Pohang University of 18
Science and Technology (POSTECH) and B.S. from Myongji University. He had worked for the development of the world first Liquid Lens at Samsung Electro-Mechanics from 2003 to 2009. Upon joining the faculty at Myongji University in 2009, he has directed the Microsystems Laboratory. And he has also served as a principal investigator in the Advanced Microfluids Engineering Research Laboratory (AMERL) since 2013. His research is in microfluidics and MEMS, including design and fabrication of micro/nano actuators and systems.
Figure Captions Fig. 1 Schematic diagram of manipulation of microparticles with two different sizes by utilizing an optothermally and acoustically excited bubble on demand. (a) Dispersed microparticles with different sizes. (b) Generation of a bubble through optothermal effects. (c) Transportation of the bubble toward the dispersed microparticles by using optothermocapillary effects. (d) Sorting and capturing of target particles with a specific size by means of acoustic radiation effects. (e) Transportation of captured particles through both optothermocapillary and acoustic radiation effects. (f) Releasing captured particles in the absence of acoustic agitation and subsequent return to the original position by way of optothermocapillary effects.
Fig. 2 Schematic of the fabrication procedures of a microfluidic chip for micromanipulation of micro-objects.
Fig. 3 Schematic diagram of the overall experimental setup for micromanipulation of mico-objects via an optothermally and acoustically excited bubble.
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Fig. 4 Size variation of optothermally-generated bubbles as a function of illumination time of laser beams with different powers. The insets illustrate sequential snapshots of bubble generation and growth.
Fig. 5 Optothermocapillary-driven bubble transportation. (a) An optothermally-generated bubble in an aqueous medium. (b–c) When a bubble is illuminated by a focused laser beam (532 nm wavelength and 300 mW power), it is stably trapped above the locally illuminated spot, and subsequently it follows along the movement of the laser beam. (d) When the laser beam is turned off, the bubble is released at the target position. Fig. 6 Capturing and repelling of micro-objects with different sizes (glass beads with 10 and 100 μm diameter) near an acoustically agitated bubble (300 μm in diameter). (a) When a bubble is acoustically agitated, it attracts large glass beads with 100 μm diameter. (b) Under the same acoustic agitation, the bubble repels small glass beads with 10 μm diameter. Here, the subscripts denote the time sequence of the capturing and repelling processes.
Fig. 7 Micromanipulation of micro-objects via a bubble based on acoustic radiation and optothermocapillary effects. (a) An optothermally generated bubble in an aqueous medium, containing particles with different sizes (glass beads with 10 μm and 100 μm diameter). (b) Sorting and capturing of particles by using acoustic radiation forces generated from an acoustically agitated bubble. (c) Transporting of captured particles (glass beads with 100 μm diameter) by using acoustic radiation and optothermocapillary forces simultaneously. (d–f) Releasing of carried particles without laser beam illumination and acoustic agitation.
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Fig. 1 Schematic diagram of manipulation of microparticles with two different sizes by utilizing an optothermally and acoustically excited bubble on demand. (a) Dispersed microparticles with different sizes. (b) Generation of a bubble through optothermal effects. (c) Transportation of the bubble toward the dispersed microparticles by using optothermocapillary effects. (d) Sorting and capturing of target particles with a specific size by means of acoustic radiation effects. (e) Transportation of captured particles through both optothermocapillary and acoustic radiation effects. (f) Releasing captured particles in the absence of acoustic agitation and subsequent return to the original position by way of optothermocapillary effects.
Fig. 2 Schematic of the fabrication procedures of a microfluidic chip for micromanipulation of micro-objects.
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Fig. 3 Schematic diagram of the overall experimental setup for micromanipulation of mico-objects via an optothermally and acoustically excited bubble.
Fig. 4 Size variation of optothermally-generated bubbles as a function of illumination time of laser beams with different powers. The insets illustrate sequential snapshots of bubble generation and growth.
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Fig. 5 Optothermocapillary-driven bubble transportation. (a) An optothermally-generated bubble in an aqueous medium. (b–c) When a bubble is illuminated by a focused laser beam (532 nm wavelength and 300 mW power), it is stably trapped above the locally illuminated spot, and subsequently it follows along the movement of the laser beam. (d) When the laser beam is turned off, the bubble is released at the target position.
Fig. 6 Capturing and repelling of micro-objects with different sizes (glass beads with 10 and 100 μm diameter) near an acoustically agitated bubble (300 μm in diameter). (a) When a bubble is acoustically agitated, it attracts large glass beads with 100 μm diameter. (b) Under the same acoustic agitation, the bubble repels small glass beads with 10 μm diameter. Here, the subscripts denote the time sequence of the capturing and repelling processes.
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Fig. 7 Micromanipulation of micro-objects via a bubble based on acoustic radiation and optothermocapillary effects. (a) An optothermally generated bubble in an aqueous medium, containing particles with different sizes (glass beads with 10 μm and 100 μm diameter). (b) Sorting and capturing of particles by using acoustic radiation forces generated from an acoustically agitated bubble. (c) Transporting of captured particles (glass beads with 100 μm diameter) by using acoustic radiation and optothermocapillary forces simultaneously. (d–f) Releasing of carried particles without laser beam illumination and acoustic agitation.
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