Microfluidics for Processing Surfaces and Miniaturizing Biological Assays

Abstract

This review is an account of our efforts to develop a versatile and flexible microfluidic technology for surface‐processing applications and miniaturizing biological assays. The review is presented in the context of current trends in microfluidic technology and addresses some of the major challenges for confining chemical and biochemical processes on surfaces: the sealing of a microchannel with a surface, the world‐to‐chip interface, the displacement of liquids in small conduits, the sequential delivery of multiple solutions, the accurate patterning of surfaces, the coincident detection of various analytes, and the detection of analytes in a small and dilute sample. Our solutions to these problems include the use of reversible sealing, capillary phenomena for powering and controlling liquid transport, and non‐contact microfluidics for spotting and drawing (on surfaces) with flow conditions. These solutions offer many advantages over conventional techniques for handling minute amounts of liquids and may find applications in lithography, biopatterning (e.g., the patterning of biomolecules), diagnostics, drug discovery, and also cellular assays.

Characterization of microfluidic human epidermal keratinocyte culture

“…The use of HEK in toxicity assays (Chou et al 2002;Didier et al 1999;Monteiro-Riviere et al 2005;Rouse et al 2006;Shvedova et al 2003) makes this cell type an attractive candidate for use in microfluidic high throughput toxicity assays. Cell culture in microfluidic systems has been demonstrated by others Delamarche et al 2005;Figallo et al 2007;Flaim et al 2005;Folch and Toner 2000;Gu et al 2004;Hui and Bhatia 2007;Hung et al 2005a, Hung et al b;Kane et al 2006;Khademhosseini et al 2004;Kim et al 2006;Leclerc et al 2006a;b;Lee et al 2006;Prokop et al 2004;Raty et al 2004;Rhee et al 2005;Sin et al 2004;Song et al 2005;Toh et al 2007;Tourovskaia et al 2005;Walker et al 2002) but keratinocytes have not yet been studied at the microscale.…”

Liquid recirculation in microfluidic channels by the interplay of capillary and centrifugal forces

“…The interfacial pressure P C of the liquid front advancing into a rectangular channel is given by [3,7]:…”

“…Immunoassays are used to detect a variety of targets from raw samples: cells, bacteria, proteins, viruses, antigens, pollutants, hormones, peptides, nucleic acids, and even pesticides [3]. The combination of microfluidics with immunoassays, specifically with surface-bound probes, has demonstrated the potential to deliver low-cost, high-sensitivity, easy-to-operate, and portable point-ofcare devices [1].…”

Surface patterning of bonded microfluidic channels

“…Channel geometries and designs vary greatly and can be extremely complex, incorporating a variety of structures from junctions for droplet formation 1,2 to multichannel networks 3,4 with tailored surface properties. [5][6][7][8] The next generation of microchips will incorporate more diverse surface functionalities in already complex geometries, requiring advanced methods for patterning the internal surfaces of the microchannels. Conventional surface modification methods which require close proximity to the substrate are restrictive when applied to microchannels due to the requirement to seal the microchip after patterning.…”