Sensors and Actuators B: Chemical
Volume 159, Issue 1, 28 November 2011, Pages 229-233
Short communicationSelective retrieval of microparticles in microchambers using electrolytically generated bubbles for cell array applications
Abstract
This paper describes a method for the selective retrieval of microparticles using bubbles generated by electrolysis. Microparticles (polystyrene beads, mouse embryos, and cell spheroids) were arrayed in microchambers fabricated in SU-8 on the surface of an electrode consisting of indium tin oxide (ITO) patterned on glass. Bubbles were selectively generated in a target microchamber by applying a voltage to electrodes positioned in the microchamber. As a result, we successfully retrieved microparticles (100 μm in diameter) positioned in the microchambers. This method is gentle enough to maintain cellular viability, and therefore, it will be a powerful tool for the quantitative analysis of cells in an arrayed system.
Introduction
Studies on an array of microparticles including microbeads or cells have remarkably advanced as tools for diagnostics [1], [2], drug discoveries [3], [4], and basic sciences [5], [6], [7], [8], [9]. Ideally, the microparticle array should also support the selective retrieval of the microparticles for subsequent analyses. In our previous study, we demonstrated a light-driven retrieval method in which bubbles are thermally generated by a laser [10]; in microscale devices, the use of bubbles is effective in generating a strong pressure [11], [12], [13] to handle objects with diameters of approximately 100 μm. However, a laser generation device is large and requires manual targeting. In addition, laser-generated bubbles may compromise cell viability due to their high temperatures. To overcome these challenges, we herein propose a method to selectively retrieve microparticles using bubbles generated by electrolysis.
Fig. 1 illustrates our method. Microparticles are arrayed in the microchambers. The microchambers are sandwiched between two ITO-coated glass substrates that function as electrodes (Fig. 1a); the ITO layer beneath each microchamber is patterned to achieve selective retrieval through separate electrical connections. When a voltage is applied between the top ITO-coated glass substrate and the patterned electrodes, an electrochemical reaction occurs at the electrodes, forming bubbles in the selected microchambers. Consequently, the bubbles displace microparticles from the selected microchambers, leading to their retrieval (Fig. 1b). The electrolysis-based method for microparticle manipulation may be more useful than the electrokinetic- [14], [15], [16], optical- [17], and ultrasonic-based [18] retrieval methods because (i) bubbles are generated with minimal heating, thereby enabling the selective retrieval of cells without damaging them, and (ii) bubbles can be easily generated without the use of large and expensive equipment to accurately target microchambers and retrieve microparticles. In this study, we demonstrate the selective retrieval of polystyrene beads and query cell viability under the condition of electrolysis.
Section snippets
Materials and methods
The process flow of the device fabrication is summarized in Fig. 2a and described as follows. (i) First, we patterned ITO on glass. S1818 photoresist was patterned by standard lithography. (ii) The ITO layer was etched using an etchant solution (HCl:H2O:HNO3 = 1:1:0.16 in ca.) for 3 min at 50 °C. (iii) After the ITO-coated glass was patterned, we fabricated microchambers using SU-8 photoresist (SU-8 100, Microchem Corp.). SU-8 was coated on the ITO layer and then patterned to create microchambers.
Results and discussion
We demonstrated the selective retrieval of microparticles (polystyrene beads and mouse embryos) trapped in microchambers (Fig. 2c). Microbeads were successfully arrayed into all the 48 microchambers of an array. We selectively retrieved the polystyrene microbeads in the microchambers, as indicated by the black arrows in Fig. 3a. When electrolysis occurred, bubbles were instantly generated only in the selected microchambers. Consequently, the trapped microbeads in those chambers were lifted up
Conclusion
We have developed a method to selectively retrieve microbeads/cells using electrolytically generated bubbles. This device is small and simple, and therefore, it can be used as a portable device for on-field use. The conditions for the retrieval step are also gentle enough to preserve cellular activity. We believe that this method will be highly effective for the quantitative analysis of cells in an arrayed format.
Acknowledgement
This work was partly supported by a Research and Development Program for New Bio-industry Initiatives (BRAIN).
Tomoaki Kurakazu received his ME degrees in Arts and Science in 2011 from the University of Tokyo, Japan. He is currently working for Tokyo Electron Ltd. in Japan.
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Tomoaki Kurakazu received his ME degrees in Arts and Science in 2011 from the University of Tokyo, Japan. He is currently working for Tokyo Electron Ltd. in Japan.
Kaori Kuribayashi-Shigetomi received her D.Phil in engineering science in 2004 from the University of Oxford, UK. Her main research interests are in the production of medical devices for minimally invasive surgery using deployable structure and MEMS technologies. She received a research fellowship (JSPS research fellow-SPD) from the Japan Society for the Promotion of Science (JSPS) for the years 2007–2009. She is currently working as a postdoctoral fellow at the Institute of Industrial Science (IIS) at The University of Tokyo.
Yukiko T. Matsunaga received her Ph.D. in material science in 2007 from Tsukuba University. 2001–2008, she focused on her research about cell micro-patterning and 3D tissue formation at Tokyo Women's Medical University. She had received Japan Society Promotion and Science (JSPS) Research Fellowship from 2005 to 2007. She is currently a project assistant professor at Institute of Industrial Science (IIS), The University of Tokyo.
Hiroshi Kimura received the Ph.D. degree in engineering from the University of Tokyo, Japan, in 2007. He is currently a research associate at Institute of Industrial Science, the University of Tokyo. He is working on microfluidic cell-engineering system for cell culture and assay.
Teruo Fujii received a Ph.D. degree in engineering from the University of Tokyo in 1993. During 1993–1995 he served as an associate professor (TOYOTA endowed chair) in globe engineering at the Institute of industrial Science (IIS), University of Tokyo. After he worked at the RIKEN Institute, he was appointed as an associate professor at Underwater Technology Research Center, IIS, University of Tokyo and moved to Center for International Research on Micronano Mechatronics (CIRMM) in 2006, where he is currently a full professor since 2007. He also served as an Advisor to MEXT (Ministry of Education, Culture Sports, Science and Technology), Japan from 2005 to 2007, and he is currently Japanese Co-director of the LIMMS-CNRS/IIS (UMI2820), a French-Japan joint lab. for Micronano Mechatronics located at IIS, University of Tokyo. His research interests are mainly in microfluidics and its applications.
Yasuyuki Sakai (Ph.D., Chemical Engineering, University of Tokyo, 1993) is a professor at Institute of Industrial Science, University of Tokyo. He is organizing Organs and Biosystems Laboratory and is working on tissue/organ engineering for clinical applications and on development of advanced in vitro micro-tissue/organ models for toxicity tests based on appropriate integration of stem/progenitor cell amplification, microfluidic, micropatterning and microsensing technologies.
Shoji Takeuchi received his Dr. Eng. degree in mechanical engineering in 2000 from the University of Tokyo. He is currently an associate professor in the Center for International Research on Micronano Mechatronics (CIRMM), Institute of Industrial Science (IIS), The University of Tokyo. He has received several awards including the Advanced Research from the Japan Society of Medical Electronics and Biological Engineering in 2001, Young Scientists’ Prize, the Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology in 2008, and the JSPS prize from the Japan Society for the Promotion of Science in 2010.
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