Page 26 - Optofluidics Fundamentals, Devices, and Applications

CHAPTER 2

Basic Microfluidic

and Soft

Lithographic

Techniques

Sindy K. Y. Tang and George M. Whitesides
Department of Chemistry and Chemical Biology, Harvard University, Cambridge,
Massachusetts

2-1 Introduction
Most optofluidic devices share a similar fluidic platform. The design,
fabrication, and operation of the fluidic systems in these devices are
based on those developed for microfluidics used in biochemical anal-
ysis. This chapter describes the basic ideas of microfluidics. We first
summarize the materials most commonly used in fabricating microflu-
idic systems and the techniques developed for fabricating them. We
then describe the characteristics of flow in these systems and illustrate
the principle of operation of some important microfluidic components.
We focus our discussion on the use of polydimethylsiloxane
(PDMS) for fabricating microfluidic systems. PDMS has been the most
widely used material in the research and development of microfluid-
ics. PDMS is an optically transparent elastomer whose stiffness can be
controlled from very soft (easily deformed by finger pressure) to much
stiffer. The fabrication of systems of microchannels in PDMS is particu-
larly straightforward. The use of PDMS as a material allows rapid pro-
totyping of devices, and facilitates the demonstration and the testing of
new concepts. The physical and chemical properties of PDMS also

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