The technique of micromolding in capillary has been employed to prepare molecularly imprinted polymer microfilaments, and to pattern MIP structures on silicon wafers. The approach relies on crosslinked poly(dimethylsiloxane) that contains relief structures as a mold to define the shape and size of the imprinted polymers. This article describes the processes leading to the fabrication of free-standing MIP micromonoliths and covalently immobilized MIP microstructures on silicon wafers. The limitations of the technique are also discussed. The development of miniaturized systems for chemical, analytical and diagnostic applications has attracted great interest recently.1,2,3 Significant advantages in speed, efficiency and control can be gained through the application of such miniature systems in laboratory testing. Micro devices have been fabricated to perform a variety of chemical and enzymatic reactions and in chip capillary electrophoresis separation. Much effort has also been devoted to shrinking analytical instruments such as high performance liquid chromatography4, combinatorial library screening system, and biosensors.6,7
Molecular recognition and interactions play central roles in these applications. Molecular imprinting, a technique for the synthesis of polymeric materials with analyte-specific recognition properties, is an attractive alternative to natural recognition systems such as antibodies and receptors.8,9,10 The ability to generate molecularly imprinted polymer (MIP) microstructures on devices should open new possibilities towards the development of miniaturized systems for chemical, analytical and diagnostic applications. The added advantages of long-term stability and chemical resistivity of MIPs may make these “intelligent chips” attractive for instrument and device fabrication.
We have employed a soft lithography11,12 technique, micromolding in capillaries (MIMIC),13,14 to fabricate MIP microstructures on silicon wafers. In MIMIC, an elastomeric stamp is placed in an intimate contact with the solid substrate. The recessed microchannels on the stamp form a network of empty capillaries. When a low-viscosity fluid precursor is placed in close contact at one end, it spontaneously fills the channels by capillary actions. Curing of the fluid leaves patterned microstructures on the substrate surface (Figure 1). An attractive feature of this technique is that the size and shape of the MIPs can be easily controlled and altered by those on the PDMS stamps. In addition, the process can be carried out conveniently in a chemical laboratory. Once the master mold is made, many elastomeric stamps can be cast and used repeatedly.