Printed Circuit Technology for Fabrication of Plastic-Based Microfluidic Devices

Sudarsan, Arjun P.; Ugaz, Victor M.

doi:10.1021/ac035411n

Cited by 44 publications

(38 citation statements)

References 20 publications

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“…Master molds were fabricated by using a printed circuit-based process (48). Soft lithography then was used to construct microchannels by heating the master to 120°C on a hot plate and making an impression of the pattern in a melt-processable thermoplastic elastomer gel substrate (49).…”

Section: Methodsmentioning

confidence: 99%

Multivortex micromixing

Sudarsan

Ugaz

2006

Proc. Natl. Acad. Sci. U.S.A.

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The ability to mix liquids in microchannel networks is fundamentally important in the design of nearly every miniaturized chemical and biochemical analysis system. Here, we show that enhanced micromixing can be achieved in topologically simple and easily fabricated planar 2D microchannels by simply introducing curvature and changes in width in a prescribed manner. This goal is accomplished by harnessing a synergistic combination of (i) Dean vortices that arise in the vertical plane of curved channels as a consequence of an interplay between inertial, centrifugal, and viscous effects, and (ii) expansion vortices that arise in the horizontal plane due to an abrupt increase in a conduit's cross-sectional area. We characterize these effects by using confocal microscopy of aqueous fluorescent dye streams and by observing binding interactions between an intercalating dye and double-stranded DNA. These mixing approaches are versatile and scalable and can be straightforwardly integrated as generic components in a variety of lab-on-a-chip systems.Dean flow ͉ expansion vortex ͉ microfluidics ͉ lab on a chip A lthough microf luidic mixing is a key process in a host of miniaturized analysis systems (1-7), it continues to pose challenges owing to constraints associated with operating in an unfavorable laminar f low regime dominated by molecular diffusion and characterized by a combination of low Reynolds numbers (Re ϭ Vd͞v Ͻ Ͻ 100, where V is the f low velocity, d is a length scale associated with the channel diameter, and v is the f luid kinematic viscosity) and high Péclet numbers (Pe ϭ Vd͞D Ͼ 100, where D is the molecular diffusivity). The relatively large discrepancy between convective and diffusive timescales implies that in a straight smooth-walled microchannel, the downstream distances over which liquids must travel to become fully intermixed (⌬y m ϳ Vd 2 ͞D ϭ Pe ϫ d) can be on the order of several centimeters. These mixing lengths are generally prohibitively long and often negate many of the benefits of miniaturization.A wide variety of micromixing approaches have been explored (8, 9), most of which can be broadly classified as either ''active'' (involving input of external energy) or ''passive'' (harnessing the inherent hydrodynamic structure of specific flow fields to mix fluids in the absence of external forces). Passive designs are often desirable in applications involving sensitive species (e.g., biological samples) because they do not impose strong mechanical, electrical, or thermal agitation. Examples of passive micromixing approaches that have been widely investigated include the following: (i) ''split-and-recombine'' strategies where the streams to be mixed are divided or split into multiple channels and redirected along trajectories that allow them to be subsequently reassembled as alternating lamellae yielding exponential reductions in interspecies diffusion length and time scales (4, 10-12); and (ii) ''chaotic'' strategies where transverse flows are passively generated that continuously expand interfacial...

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Section: Methodsmentioning

confidence: 99%

Multivortex micromixing

Sudarsan

Ugaz

2006

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

287

221

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“…In the first method, actuation electrodes were patterned on PCB substrates by using photolithography, in a manner similar to what has been reported for other applications. [24,25] This method is fast, inexpensive, and easy relative to conventional microfabrication. In the second technique, actuation electrodes were patterned directly onto substrates using a desktop laser printer; this method enabled ultra-highthroughput fabrication.…”

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confidence: 99%

Rapid Prototyping in Copper Substrates for Digital Microfluidics

Abdelgawad

Wheeler

2006

Advanced Materials

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Microfluidics, a technology based on enclosed, micrometerdimension channels, first became popular in the early 1990s [1,2] as a tool for miniaturizing chemical analyses. Recently, a new form of "digital microfluidics" (DMF) has emerged, in which droplets of liquid are manipulated on an array of electrodes by means of electrowetting [3,4] and/or dielectrophoresis. [5][6][7][8] There is currently much enthusiasm for DMF, [9] as the device geometry seems a perfect match for array-based biochemical applications, such as enzyme assays [10,11] and profiling proteomics. [12][13][14] Despite this enthusiasm, the arduous procedure required to fabricate DMF devices, which typically requires metal deposition, photolithography, wet-etching, deposition or thermal growth of a dielectric layer, and deposition of a hydrophobic coating, [3,4,[11][12][13][14][15][16][17][18][19] is a barrier to its growth and development. Consequently, DMF devices are limited to use in a few laboratories worldwide.The availability of an accessible microfabrication technique is critical for the growth and continued development of DMF. An analogy can be made to the state of conventional, channel-based microfluidics in the mid-1990s. A database search reveals that approximately eight articles per year were published on the subject of channel microfluidics in 1992-1998; this number exploded to approximately 53 articles per year in 1999-2000.[20] This jump in popularity, which has greatly expanded the scope and range of applications for channel microfluidics, was driven in part by increased accessibility resulting from rapid prototyping microfabrication methods. [21][22][23] We report here, for the first time, two rapid prototyping techniques for the fabrication of DMF chips, making use of commercially available printed circuit board (PCB) substrates. In the first method, actuation electrodes were patterned on PCB substrates by using photolithography, in a manner similar to what has been reported for other applications. [24,25] This method is fast, inexpensive, and easy relative to conventional microfabrication. In the second technique, actuation electrodes were patterned directly onto substrates using a desktop laser printer; this method enabled ultra-highthroughput fabrication. We anticipate that these methods will increase the accessibility of DMF, an effect that will significantly expand the impact of this promising technology. The first rapid prototyping method, relying on photolithography, was used to form devices from two kinds of substrates: industrial-grade flexible sheets (9 lm thick copper on 50 lm polyimide) and low-grade inflexible boards (35 lm thick copper). Prior to use, devices were coated with Parylene-C (see Experimental section) or poly(dimethyl siloxane) (PDMS) as a dielectric layer, and then coated with Teflon-AF. Devices formed in this manner were used to actuate droplets sandwiched between two plates, as depicted in Figure 1a. This configuration is the most popular, as it is capable of performing all of the critical fluidic oper...

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“…7,8 Recently, soft lithography is the most popular fabricating technique because it is cheaper, easier and faster to produce a microfluidic platform on polydimethylsiloxane (PDMS). [6][7][8][9][10][11] The fabrication process consists of two main steps: master mold building and the replication of a PDMS chip from a master mold. There are different ways to construct a master mold, e.g., by patterning dense photoresist meterials on a silicon substrate, 12 etching into a silicon or glass substrate using conventional micromachining processes, 13 the patterning of a UV-cured epoxy resin on a brass block, 14 precision milling the pattern into an aluminium alloy substrate, 15 direct printing of the pattern on a transparency with a laser printer 16 and etching into a photosensitized printed circuit board (PCB) using conventional printed-circuit technology.…”

Section: Introductionmentioning

confidence: 99%