Paper-based microfluidic devices: A complex low-cost material in high-tech applications
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ntroduction The use of paper as a novel device platform has gained increasing interest during the last decade with an emphasis on paperbased microfluidic diagnostic applications. Paper-based fluidic devices are low cost, easy to use, and disposable when compared to their classical counterparts constructed from glass or silicon.1 Advances in fabrication techniques as well as novel methods for manipulating fluid streams within the paper sheet exhibit promising high levels of multiplexing and greater assay diversity than existing simple paper-based dipstick tests.2 Nevertheless, a closer look at the current literature in paper-based microfluidics presents a rather clear picture— although a “diagnostics for all” is certainly a valid goal to be achieved, and there have been a large number of interesting platforms introduced by materials scientists, chemical engineers, and physicists to date, the number of ready-to-use devices in the market is limited. Unraveling the causes that limit development of paper-based microfluidics may reveal needs that must be addressed for successful design of a paperbased device. These include: 1. The paper material itself. It provides the necessary open porous structure to transport liquids by capillary action. What do we know about paper? Does it matter whether we take ordinary filter paper off the shelf or should it be a more
sophisticated paper substrate instead? What is the role of the chemical and morphological constitution of the paper material? Does the origin of the paper fibers, the fiber thickness, or the sheet porosity of the paper matter, and how? 2. The definition of hydrophobic barriers. Such barriers are needed to confine fluid flow inside locally defined areas. Among the issues in the design of paper-based microfluidic devices, the formation of such barriers (e.g., by wax printing or any other hydrophobic substance) may be considered well understood and a number of recent reviews have carefully summarized the various techniques in detail.3–5 3. The type of analyte (e.g., biomarker) to be detected. It defines the type of chemical-sensing elements to be immobilized in the paper structure. Examples range from DNA to proteins (e.g., antibodies) and to various molecules. What is the most efficient immobilization strategy? A large number of different demonstration devices have been reported to date and have been addressed in other reviews.4,5 4. Control of capillary fluid flow. Controlled liquid transport is essential for obtaining reproducible results for the sensitivity of a paper-based sensor. If, for example, the fluid is transported within the paper at a too high rate, the analyte to be detected may not reach the sensing sites and thus will not contribute to a detection signal. If the capillary-driven
A. Böhm, Thermo Fisher Scientific, Germany; alexander.boehm2@thermofisher.com M. Biesalski, Technische Universität Darmstadt, Germany; [email protected] doi:10.1557/mrs.2017.92
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• www.mrs.org/bulletin MRShttps:/www.cambridge.org/core. BULLETIN • VOLUME 42 • MAY 2017 © 2017 Materials Res
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