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▪ Abstract  Polysilicon surface micromachining is advancing significantly and many new applications are moving beyond the prototyping phase. Recent technical successes are leading to excitement concerning various uses of devices in optical, wireless, sensor, and many other areas. Incorporation of state-of-the-art integrated circuit (IC) fabrication methods, such as planarization by chemical mechanical polishing (CMP), has enabled extension to a five-level technology. This has opened significant design space, especially for microactuator applications. Recent advancement of in situ microdiagnostics for materials and surface properties has enhanced our understanding of device reliability and performance and will allow devices to operate near well-known materials limits. New IC-compatible materials will further enhance the capabilities of microsystems in terms of performance, reliability, and operation in harsh environments.

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This work describes the performance of poly(methyl methacrylate) (PMMA) microfluidic DNA purification devices with embedded microfabricated posts, functionalized with chitosan. PMMA is attractive as a substrate for creating high surface area (SA) posts for DNA capture because X-ray lithography can be exploited for extremely reproducible fabrication of high SA structures. However, this advantage is offset by the delicate nature of the posts when attempting bonding to create a closed system, and by the challenge of functionalizing the PMMA surface with a group that invokes DNA binding. Methods are described for covalent functionalization of the post surfaces with chitosan that binds DNA in a pH-dependent manner, as well as for bonding methods that avoid damaging the underlying post structure. A number of geometric posts designs are explored, with the goal of identifying post structures that provide the requisite surface area without a concurrent rise in fluidic resistance that promotes device failure. Initial proof-of-principle is shown by recovery of prepurified human genomic DNA (hgDNA), with real-world utility illustrated by purifying hgDNA from whole blood and demonstrating it to be PCR-amplifiable.