Fabrication of Microfluidic Devices for Biological Applications
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Fabrication of Microfluidic Devices for Biological Applications Christina Morales 1 , Carl Hansen 2 , Stephen Quake 2 , and Frank A. Gomez 1 Department of Chemistry and Biochemistry, California State University, Los Angeles 1 Department of Applied Physics, California Institute of Technology 2 Abstract: The past ten years have witnessed tremendous advances in the design and use of microelectromechanical systems (MEMS). Applications for microfluidic devices have proliferated at a speed reminiscent of the explosive use of microelectronics after the integrated circuit was invented. Microfluidic technology or Lab-on-chip technology offers many potential benefits in chemistry, biology, and medicine, not least of which is to automate work while reducing the use of expensive chemical reagents to nanoliter and sub-nanoliter scale. Microfluidic systems have been shown to have great potential in a diverse array of biological applications including biomolecular separations, enzymatic assays, immunhybridization reactions, and the polymerase chain reaction. Recent advances in MEMS has employed the use of multilayer soft lithography (MSL). Here, layered structures are constructed by binding layers of elastomer each of which is separately cast from a micromachined mold. Herein, we describe the design, development, and fabrication of novel microfluidic devices for use in capillary electrophoresis (CE) and other applications. Prospects for future applications are discussed. Introduction: Microfluidics lab-on-a-chip technology was born out of a need to automate the wet lab in the field of biotechnology. Soft lithography has allowed for the design and development of microfluidic channels in the range of micro- to picometers. Polydimethylsiloxane (PDMS), a silicone elastomer capable of bonding many layers, is currently used to manipulate solutions containing, DNA, blood samples, and proteins. Within the last ten years researchers have advanced the microvalve concept and technology to a highly reproducible level. Next generation chips will be self-contained and inexpensive as reagent costs will be reduced by sub-nanoliter reaction chambers. With a turn around time of 24-48 hours from design (using AutoCAD data files) to experimentation, prototyping problems will become a thing of the past. Discussion: The theory of microfluidics stems from micromechanical systems (MEMS) with adaptations to solutions-based wet labs of biological technology. Figure 1 shows a CAD file for a standard two (flow and control) layer push up device. A high resolution printer (20,000 dpi.) then prints two transparencies, one for each layer. Figure 2 shows a UV curable photoresist being spun onto a 3 inch silicon wafer to be exposed in figure 3. Microvalve methodology is the underlying basis of all microfluidic chips, as orthogonal channels are actuated and a valve is formed. Figure 5 gives an example of how polydimethylsiloxane (PDMS) is spun at varying speeds for the desired thickness of one of the layers. The two layers are then baked separately. They are then aligned by hand in a class 1000 clean room under a high powered stereoscope. Figures 5 and 6 show the assembled chips ready for experimentation. Figure 7 shows a peristaltic or rotary mixing circle used for combining liquids. Figure 8 shows an actual application of microfluidics being used, the crystallization of lysine. Figure 9 is a characterization of how a microvalve is formed. Conclusion: Researchers have gained enough experience in the new technologies of UV curable photolithography and silicone based elastomers of PDMS to control channel heights and widths of microfluidic chips. Reaction chambers, mixing devices and multiplexers have been devised to control sub-nanoliter volumes of liquid. Future applications of microfluidics will be expanded to include rapid blood screening, DNA sequencing, bacterial growth and engineering, single molecule detection and advanced techniques in protein synthesis. Acknowledgments: Dr. Stephen Quake, Dr. Axel Scherer, Dr. Carl Hansen, Sebastian Maerkl and Joshua Marcus. The authors gratefully acknowledge financial support for this research by grants from the National Science Foundation (DMR-0351848, DMR-0080065, CHE-0136724, CHE-0515363) and the National Institutes of Health (R15 AI055515- 01 and 1 R15 AI065468-01). Figure 1. Design & Print Mask From CAD File Figure 4. Create Chip From PDMS based Multi-Layer Soft Lithography Figure 2. Spin Photoresist onto A Silicon Wafer Figure 6. Air Flow Regulators for Automated Experimentation Figure 5. A Mounted Microfluidic Chip Figure 8. Crystallized Lysine, Ready for direct use in X-ray Crystallography Figure 7. Peristaltic Mixing Circle Fluidigm Figure 9. A Microvalve with the Control Layer on top Figure 2. Expose Pattern With UV Light
Transcript of Fabrication of Microfluidic Devices for Biological Applications
Fabrication of Microfluidic Devices for Biological ApplicationsChristina Morales1, Carl Hansen2, Stephen Quake2, and Frank A. Gomez1
Department of Chemistry and Biochemistry, California State University, Los Angeles1
Department of Applied Physics, California Institute of Technology2
Abstract:The past ten years have witnessed
tremendous advances in the design and useof microelectromechanical systems (MEMS).Applications for microfluidic devices haveproliferated at a speed reminiscent of theexplosive use of microelectronics after theintegrated circuit was invented. Microfluidictechnology or Lab-on-chip technology offersmany potential benefits in chemistry, biology,and medicine, not least of which is toautomate work while reducing the use ofexpensive chemical reagents to nanoliter andsub-nanoliter scale. Microfluidic systemshave been shown to have great potential in adiverse array of biological applicationsincluding biomolecular separations,enzymatic assays, immunhybridizationreactions, and the polymerase chainreaction. Recent advances in MEMS hasemployed the use of multilayer softlithography (MSL). Here, layered structuresare constructed by binding layers ofelastomer each of which is separately castfrom a micromachined mold. Herein, wedescribe the design, development, andfabrication of novel microfluidic devices foruse in capillary electrophoresis (CE) andother applications. Prospects for futureapplications are discussed.
Introduction:Microfluidics lab-on-a-chip technology
was born out of a need to automate the wetlab in the field of biotechnology. Softlithography has allowed for the design anddevelopment of microfluidic channels in therange of micro- to picometers.Polydimethylsiloxane (PDMS), a siliconeelastomer capable of bonding many layers, iscurrently used to manipulate solutionscontaining, DNA, blood samples, andproteins. Within the last ten yearsresearchers have advanced the microvalveconcept and technology to a highlyreproducible level. Next generation chips willbe self-contained and inexpensive as reagentcosts will be reduced by sub-nanoliterreaction chambers. With a turn around timeof 24-48 hours from design (using AutoCADdata files) to experimentation, prototypingproblems will become a thing of the past.
Discussion: The theory of microfluidics stems frommicromechanical systems (MEMS) withadaptations to solutions-based wet labs ofbiological technology. Figure 1 shows a CADfile for a standard two (flow and control) layerpush up device. A high resolution printer(20,000 dpi.) then prints two transparencies,one for each layer. Figure 2 shows a UVcurable photoresist being spun onto a 3 inchsilicon wafer to be exposed in figure 3.Microvalve methodology is the underlyingbasis of all microfluidic chips, as orthogonalchannels are actuated and a valve is formed.Figure 5 gives an example of howpolydimethylsiloxane (PDMS) is spun atvarying speeds for the desired thickness ofone of the layers. The two layers are thenbaked separately. They are then aligned byhand in a class 1000 clean room under a highpowered stereoscope. Figures 5 and 6 showthe assembled chips ready forexperimentation. Figure 7 shows a peristalticor rotary mixing circle used for combiningliquids. Figure 8 shows an actual applicationof microfluidics being used, the crystallizationof lysine. Figure 9 is a characterization of howa microvalve is formed.
Conclusion:Researchers have gained enough
experience in the new technologies of UVcurable photolithography and silicone basedelastomers of PDMS to control channelheights and widths of microfluidic chips.Reaction chambers, mixing devices andmultiplexers have been devised to controlsub-nanoliter volumes of liquid. Futureapplications of microfluidics will be expandedto include rapid blood screening, DNAsequencing, bacterial growth andengineering, single molecule detection andadvanced techniques in protein synthesis.
Acknowledgments: Dr. Stephen Quake, Dr. Axel Scherer,
Dr. Carl Hansen, Sebastian Maerkl andJoshua Marcus. The authors gratefullyacknowledge financial support for thisresearch by grants from the National ScienceFoundation (DMR-0351848, DMR-0080065,CHE-0136724, CHE-0515363) and theNational Institutes of Health (R15 AI055515-01 and 1 R15 AI065468-01).
Figure 1. Design & Print MaskFrom CAD File
Figure 4. Create Chip From PDMS basedMulti-Layer Soft Lithography
Figure 2. Spin Photoresist ontoA Silicon Wafer
Figure 6. Air Flow Regulatorsfor Automated Experimentation
Figure 5. A Mounted Microfluidic Chip
Figure 8. Crystallized Lysine, Ready fordirect use in X-ray Crystallography
Figure 7. Peristaltic Mixing Circle
Fluidigm
Figure 9. A Microvalve with theControl Layer on top
Figure 2. Expose PatternWith UV Light
