Introduction - Hardware/Software Co-Design and Optimization for Cyberphysical Integration in Digital Microfluidic Biochips - page 1

Chapter 1
Introduction
Microfluidic biochips have emerged as powerful and reliable toolkits for
biotechnology applications, such as chemical synthesis, the diagnosis of diseases,
and the development of new drugs [ 1 - 3 ]. Nanoliter and picoliter volumes of
biological samples can be manipulated on microfluidic devices under software
control. Compared to conventional devices and analyzers, microfluidic devices offer
many unique advantages. The low volume of samples and reagents manipulated on
microfluidic devices can significantly reduce the costs associated with conducting
experiments; the precise control of reactions on microfluidic devices can enhance
the accuracy of the experiments; the time required for the chemical reactions to
occur at the nanoliter scale can be greatly reduced due to the high surface-to-
volume ratios. Based on the methods used to manipulate the liquid on the chip,
microfluidic biochips are categorized as “flow-based chips” or “digital (droplet-
based) chips” [ 4 , 5 ].
In continuous-flow chips, liquid flow on the biochip is achieved through micro-
fabricated channels, pumps, and valves [ 6 , 7 ]. To overcome fluidic resistance, liquid
in the channels is driven by external pressure sources. Such sources include exter-
nal mechanical pumps and integrated, mechanical micropumps. The pressure
required for liquid flow can also be provided by combinations of capillary forces
and electrokinetic mechanisms [ 6 ]. In recent years, the development of flow-
based microfluidic devices has been accelerated by innovations in fabrication
techniques, including the application of polydimethylsiloxane (PDMS) and the
dense integration of active microvalves. From the early days, when flow-based
biochips had simple topologies and only a few channels, commercial flow-based
microfluidic devices today have large-scale networks of channels, and they can be
used in various real-world applications. For example, a product from Fluidigm [ 8 ],
a biotechnology company that focuses on flow-based microfluidic biochips, can
perform a series of gene analyses, including enrichment for target DNA sequences,
sample barcoding for multiplexed sequencing, and preparation of the sequencing
library.