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