Surface Modification of Microfluidic Devices using a Zwitterionic Polymer

 

This project will: develop a novel procedure to modify the surface of a microchip

 

Primary Faculty co-Advisors:

            Isiah Warner, Chemistry Department (Chemical Separations)

            Steven Soper, Chemistry Department (Micro-instrumentation, Chemical Separations)

            Rezik Agbaria, Chemistry Department (Fluorescence Spectroscopy)

            Nicole Gill, Chemistry Department (Polymer Science)

 

Technical Proposal:  The goal of this project is to develop a novel method for the enhancement of analytical separations (i.e. microchip capillary electrophoresis).  This research involves the use of a zwitterionic polymer as well as other polymers as surface modifiers for microchip capillary electrophoresis.  The former is ideally suited for the separation of analytes such as peptides, proteins, and chiral compounds. 

Microchip Electrophoresis

            In the past decade, microchip capillary electrophoresis (CE) has risen from an academic concept to a commercial product.¹  This technology has proven to be a valuable tool for creating miniaturized devices for application in many chemical and biochemical assays.  The attractive features associated with these devices are potential for system integration in which various processing steps of the assay are included onto the fluidic platform, rapid analysis speeds, construction of highly multiplexed systems, the ability to reduce reagent consumption, and the mass production of devices at minimal costs.²  Initial work on microchip CE focused on microfabrication in glass and quartz because of the mature mirocmachining technology available for these materials.  With the use of glass and quartz, many of the properties for conventional CE were maintained due to their chemical similarity to fused silica.

            However, there are several disadvantages to the use of glass.  The devices required are expensive to set up and maintain.  Also, the fabrication process produces one chip, which, if broken, is useless.  Optical-quality glass and quartz are expensive as compared to plastics and polymers, which raises the cost of each device.  Also, the fabrication process produces a permanent seal between the two plates that make up the device.  If the channel clogs, the device is ruined.

            The disadvantages of glass microchips have led to the investigation of alternative substrate materials for the construction of CE microchips.  Several types of polymer substrates are advantageous because they are significantly less expensive than glass, are not as fragile as glass and they can be mass-produced.

            In this project, poly(methyl methacrylate) [PMMA] will be used for the fabrication of the plastic chips employed in microchip electrophoresis.  Fabrication of the microchips will be done in the lab of Dr. Soper.  Figure 1 shows the chemical structure of PMMA, Figure 2 shows the fabrication process for the microchips while Figure 3 shows the diagram of the chip.

 

 

 

 

 

                                                                                   

 

 

 

 

 

 

 

 

 

 

 

 

 

                   Figure 1.  Chemical structure of poly(methylmethacrylate) (PMMA).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

       Figure 2.  Fabrication process for the microchip device.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                     

 

           Figure 3.  Diagram of microchip fabricated in the lab of Dr. Soper.

 

 

 

Zwitterionic Polymer

            For the surface modification of  the microfluidic channels, a zwitterionic polymer,

poly-3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate (PDMAPS), will be tested first.  PDMAPS is in a special class of zwitterions called sulfobetaines.  Sulfobetaines have an ammonium cation and a sulfonic anion isolated with an alkyl, usually propyl or butyl group.  Based on results reported by Schulz et al.⁴, PDMAPS is considered to be in a collapsed coil  in water below UCST (upper critical solutions temperature) due to intra-and/or inter-chain associations.  This state is disrupted by addition of salt, thereby allowing the chain expansion and solubilization due to screening effects of both ions.⁵  Figure 3 shows the chemical structure of the monomer of PDMAPS:

 

Figure 3.  Chemical structure of  3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate (DMAPS).

 

 

Polymerization/Characterization of PDMAPS

            Polymerization of DMAPS will be done in Warner's lab and characterized using  advanced methods specifically for characterization of macromolecules.

 

Study of Surface Modification of PMMA Microchips

            Upon completion of the characterization of PDMAPS, different strategies will be facilitated to properly modify the channel wall of the microchip with the zwitterionic polymer.  Scanning Electron Microscopy (SEM) will be used to investigate the coating thickness adsorbed onto the channel wall. 

 

Once the polymer has been successfully synthesized/characterized and a successful coating has been established, the performance of the modified microchip will be tested and compared to the performance of an unmodified microchip.  In this case a mixture of commonly used fluorescent dyes will be separated and analyzed in both chips to compare their performances (i.e. peak efficiency, resolution).

 

Students involved in this research will be exposed to a variety of analytical techniques.  The students will learn the fundamentals of polymer chemistry and separation science.  With the successful completions of the modified microfluidic device, the students will have developed a more efficient separation technique for the analysis of a vast amount of chemical compounds.

 

Number of IGERT apprentices to be recruited and probable home departments:

Two from Chemistry

 

Consistency with the Macromolecular Education, Research & Training theme:

This project requires students to understand the process of synthesizing polymers, as well as understanding synthetic polymers used for microfabrication, and understanding methods used for characterizing these macromolecules.

 

How does the project form a vector cross-product of existing research themes by the participants?

Existing research directions.  Warner’s group has been involved with the separation of compounds using capillary electrophoresis for almost a decade.  Soper’s group has focused on fabricating microfluidic devices using PMMA instead of traditional glass-based substrates.  His group has also used these devices for the high-throughput analysis of DNA for sequencing and diagnostic applications.

New research direction.  This project will bring together these two research groups for the first time to develop new methodologies and technologies.  This research project will lead to new advances in microchip electrophoresis.

 

How do students benefit from the team-oriented research, beyond what would be available to them from either advisor separately?

Using microfluidic devices has become exceedingly popular over the last decade.  The student from Warner’s group will gain a deeper understanding of the use of microchip electrophoresis from Professor Soper. 

References:

1.  Manz, A.; Graber, N.; Widmer, H. M.  Sensors and Actuators, B:  Chemical  (1990),  B1(1-6),  244-8.

2.  Galloway, Michelle; Stryjewski, Wieslaw; Henry, Alyssa; Ford, Sean M.; Llopis, Shawn; McCarley, Robin L.; Soper, Steven A.   Analytical Chemistry  (2002),  74(10),  2407-2415.

3.  Liu, Yan; Fanguy, Joseph C.; Bledsoe, Justin M.; Henry, Charles S.  Analytical Chemistry  (2000),  72(24),  5939-5944.

4.  Schulz, D. N.; Peiffer, D. G.; Agarwal, P. K.; Larabee, J.; Kaladas, J. J.; Soni, L.; Handwerker, B.; Garner, R. T.  Polymer  (1986),  27(11),  1734-42.

5.  Chen, L.; Honma, Y.; Mizutani, T.; Liaw, D.-J.; Gong, J. P.; Osada, Y.  Polymer  (1999),  Volume Date 2000,  41(1),  141-147.