Materials Aspects in Micro- and Nanofluidic Systems Applied to Biology
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Materials Aspects
in Micro- and Nanofluidic Systems Applied to Biology
Olgica Bakajin, Eric Fountain, Keith Morton, Stephen Y. Chou, James C. Sturm, and Robert H. Austin Abstract One of the key problems in microfabrication and especially nanofabrication applied to biology is materials selection. Proper materials must have mechanical stability and the ability to hermetically bond to other surfaces, yet not bind biological molecules. They must also be wettable by water and have good optical properties. In this article, we review some of the attempts to find materials for micro- and nanofluidic systems in biological applications that satisfy these rather conflicting constraints. We discuss the materials properties that make poly(dimethylsiloxane) or non-elastomeric materials more or less suitable for particular applications in biology. We also explore the effects and the importance of surface treatments for integrating biological objects into microfabricated and nanofabricated fluidic devices. Keywords: biological, fluidics, nanoscale, surface chemistry.
Introduction Biological molecules and silicon technology have an uneasy relationship, yet each needs the other. Micro- and nanofluidic systems that have been used for DNA analysis, studies of protein folding, and cell separation offer several advantages over conventional macroscopic methods. Microfluidic systems are commonly associated with micro total analysis systems, which perform all the necessary analytical steps automatically on a single chip, with applications in biosensing and medical diagnostics or drug delivery.1,2 Micro- and nanotechnology, however, are also enabling unprecedented advances in the study of biological physics.3–5 We can now investigate single-molecule dynamics and perform experiments faster and with considerably lower consumption of
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precious sample volumes. Microfluidic devices reduce analytical sample consumption by many orders of magnitude, which is especially important when heavily engineered molecules are used, such as proteins labeled with fluorophores for Foerster resonance energy transfer (FRET) analysis. Nanotechnology has the potential to revolutionize biology through the construction of chip-based devices that can not only detect and separate single DNA molecules by size, perform restriction mapping on single DNA molecules, and study DNA protein interactions, but also hopefully separate the rare one-in-amillion cell, analyze it, and sequence single DNA molecules. The confinement of DNA, which has a persistence length of 50 nm in double-stranded form, in
nanofluidic channels has enabled studies of DNA protein interactions on a singlemolecule level.6,7 Due to the reduction in the size of the structures around which the fluids flow, the Reynolds number is, however, typically much less than 1, even at velocities of 10 cm/s in microstructures, so that alternatives to turbulence must be found in order to generate three-dimensional flows to mix reagents efficiently. Reduced dimensions, on the other hand, allow samples to diffuse
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