The two step Berkeley Lab process enables covalent attachment of the monolith to the channel walls and dramatically enhances the adhesion - a result no other method has been able to achieve.

APPLICATIONS OF TECHNOLOGY:

Concentrating, reacting, separating, and
identifying compounds in systems involving:

• Microreactors
• Lab-on-a-chip
• Protein and peptide mapping
• Capillary chromatography and
  electrochromatography
• Detection of chemical and biological agents
• Micro solid phase extraction (SPE)
• Environmental analysis and monitoring

ADVANTAGES:

• Allows use of plastic chips mass produced via inexpensive dry techniques
• Eliminates voids at the monolith/channel interface
• Avoids undesirable adsorption of processed compounds at the channel walls
• Simplifies and accelerates functionalization via UV initiated grafting
• Minimizes consumption of precious or custom prepared monomers
• Accommodates monomers with almost any chemistry
• Dramatically increases the surface density of functionalities
• Facilitates spatial control of functionalization within the microchannels
  

ABSTRACT:

Jean Fréchet, Frantisek Svec, and Thomas Rohr have used photoinitiated grafting to develop plastic microfluidic substrates, place porous polymer monoliths within the channels, and modify the pore surface of these monoliths to improve device performance.

The Berkeley Lab researchers have overcome the undesirable absorption characteristics typical of the microchannel surfaces in thermoplastic chips by using simple UV triggered functionalization, eliminating the major obstacle to commercial development of these chips. Polymeric microfluidic substrates are advantageous because they can be fabricated using inexpensive techniques such as injection molding or hot embossing instead of the expensive multistep wet fabrication that is required to produce chips from inorganic substrates.

A technology developed earlier by Fréchet, Svec, and colleagues entails the fabrication of porous polymer monoliths within microfluidic channels using photoinitiated polymerization. This process uses a photolithographic technique - irradiation through a mask - to prepare the monolithic polymer only in desired areas of the microchannels. The present invention expands the use of UV radiation and masking to graft functionalities to both the channel walls and the polymer monolith. Although photografting has been used for two dimensional flat surfaces before, the Berkeley Lab group is the first to demonstrate its use for three dimensional highly crosslinked porous polymers, which were assumed to be too opaque or diffractive for the process.

Photoinitiated grafting allows tailoring of surface chemistry in specific locations of the porous monolith. This spatial control of functionality is very difficult to achieve with non-grafting techniques currently in use such as direct copolymerization, classical chemical modification, or with grafting initiated by means other than UV light.

Modifying and functionalizing the surface of the microchip via photoinitiated grafting (i) makes the wall non-adhesive for the processed compounds and (ii) prevents formation of voids at the monolith/channel interface, thus improving the overall performance of the device. The two step process enables covalent attachment of the monolith to the channel walls and dramatically enhances the adhesion - a result no other method has been able to achieve. In addition, grafting chains of functional polymers to the active sites at the surface of pores within the monolith allows multiple functionalities to emanate from each site and leads to a significant increase in the number of functionalities.

The Berkeley Lab UV initiated grafting technique is mediated by hydrogen abstracting photoinitiators and can be used with all materials that have sufficient UV transparency. The process also enables the consecutive grafting of monomers onto the monolith’s pore surfaces to create layered chemistries.

STATUS:

• Issued Patent # 7,431,888. Available for licensing or collaborative research.

FOR MORE INFORMATION:

Rohr, T., Ogletree, F.D., Svec, F., Fréchet, J.M., “Photografting and the Control of Surface Chemistry in Three-Dimensional Porous Polymer Monoliths,” Macromolecules 2003, 36, 1677-84.

Stachowiak, T.B., Rohr, T., Hilder, E.F., Peterson, D.S., Yi, M., Svec, F., Fréchet, J.M., "Fabrication of Porous Polymer Monoliths Covalently Attached to the Walls of Channels in Plastic Microdevices,” Electrophoresis 2003, 24, 3689-93.

Peterson, D.S., Rohr, T., Svec, F., Fréchet, J.M., “Dual-Function Microanalytical Device by In Situ Photolithographic Grafting of Porous Polymer Monolith: Integrating Solid- Phase Extraction and Enzymatic Digestion for Peptide Mass Mapping,” Anal. Chem. 2003, 75, 5328-35.

Rohr, T., Ogletree, F.D., Svec, F., Fréchet, J.M., “Surface Functionalization of Thermoplastic Polymers for the Fabrication of Microfluidic Devices by Photoinitiated Grafting,” Adv. Funct. Mater. 2003, 13, 264-70.

REFERENCE NUMBER: IB-1829

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