Biomedical Engineering Reference
In-Depth Information
7.1
Introduction to Microfluidics
Microfluidics refers to the manipulations of fluids in a volume that has at least
one dimension less than 1 mm. Microfluidic devices refer to tools that execute
these manipulations. Various advanced fabrication technologies enabled researchers
to create the micro-/nano-features to reduce the volume of working solution of
many biological experiments from milliliters (10 3 L in a Petri dish or a tube)
to microliters (10 6 L), nanoliters (10 9 L), and even femtoliters (10 15 L). The
miniaturization of many biochemical reactions became the research focus with
the development of chip technology, and various concepts such as “micro total
analysis system (
TAS)” and “lab-on-a-chip” were proposed [ 1 ]. These terms are
essentially synonymous and have more extensions such as parallel operation and
integration of traditionally separate operation units. In addition to the perceived
advantages (such as larger throughput, lower sample consumption, less time) made
possible by the miniaturization, the change of physical dimensions bring about
many unique properties at microscale [ 2 ]. Fully understanding and interpretation
for the microscale phenomena lead to new techniques and experiments originally
impossible at the macroscale.
The low Reynolds number of microfluids determined that the fluid flow is
laminar. As a consequence, two or more microfluid streams contacted with each
other cannot be mixed within a short path or a reasonable time, and flow-patterning
techniques utilizing laminar flow and micro-mixers against laminar flow emerged.
However, molecule or particle diffusion as a result of Brownian motion is a general
phenomenon and causes the mixing of laminar flows, which can be used for the
study of reaction kinetics. Because of the small length scale in miniaturized devices,
the time it requires for diffusion in microscale is shortened compared to that in
macroscale. The surface area to volume ratio at the microscale is much larger so that
heat transfer is much faster, which was utilized for efficient capillary electrophoresis
with higher resolution. Surface tension at the microscale is also significant, which
has been extensively studied for droplet production and manipulation. The large-
scale integration of micro-compartments allows one device to possess multiple
functions.
Microfluidic devices offer the opportunity to access unexplored domains in
biological or chemical analysis, and the achievement especially for DNA analysis
will be discussed in following sections.
7.2
Qualitative Analysis
A microfluidic chip could integrate different chemical steps and separate compo-
nents within a stand-alone device. The powerful tools provide many wonderful
solutions that aim to decrease sample consumption, lower cost, fasten the process,
and improve the convenience of operation.
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