Biomedical Engineering Reference
In-Depth Information
improve, new microfluidic applications in enzymatic assays, genomics, proteomics,
and clinical pathology are becoming feasible [ 1 - 5 ].
Combining microfluidics with the power of electronics is a recent and growing
trend empowering many new biological and medical applications. Microelectronics
offer new and exciting ways to position and analyze cells and fluids [ 6 - 9 ]. They
enable tremendous miniaturization, greater accuracy, discrete sample handling, and
the ability to perform hundreds or even thousands of functions in parallel.
Integrated circuits (ICs) have the ability to empower even further miniaturiza-
tion and complexity of biomanipulation and analysis devices. Integrated circuits
combine the power of programmability with CMOS technology to fit billions
of transistors on a single chip. Hybrid integrated circuits/microfluidic chips are
capable of performing intricate manipulations and analysis on single cells and small
chemical volumes [ 5 , 10 - 17 ]. These devices pave the way for a new generation
of miniaturized biomedical experiments which can be performed on single drops of
human physiological fluids to diagnose illness and disease in a point-of-care setting.
Currently, the analysis of human physiological fluids is an often unpleasant and
slow process. A large and painful syringe is first used to collect blood samples,
after which the sample must be sent to a laboratory for analysis, delaying the
results by days [ 18 ]. The vision driving integrated circuits/microfluidic technology
is to take hundreds of existing tests and perform them quickly and simultaneously
using a single nanoliter droplet of body fluid. The tests will be completed at the
patient's bedside and, in minutes, empowering doctors with real-time knowledge of
the patient's condition. The tests can also be performed in resource-limited settings
such as developing countries, remote locations, and war zones.
Figure 2.1 shows an illustration of a hybrid integrated circuit/microfluidic chip
for point-of-care diagnostics. Cells and reagents enter the device through inlets.
Single cells and droplets are pinched off into the microfluidic chamber. The
integrated circuit then positions the cells and droplets using electric fields. Sensors
built into the integrated circuit analyze various properties of the cells and droplets
and monitor the outcomes of chemical reactions.
Numerous new technologies and methods are needed to make integrated circuits
for point-of-care diagnostics a reality. Many have already been developed and many
more are in the pipeline. This chapter presents an overview of the current state of
the field and a vision of future work needed to make ICs a reality in point-of-care
diagnostics. Table 2.1 below summarizes functions which can be performed and on
IC/microfluidic chips.
Principles of Dielectrophoresis
Most functions listed in the summary table above make use of electrical phenomena
to manipulate and analyze droplets and cells. Dielectrophoresis is the bedrock
phenomenon used to transport droplets. Electroporation and dielectric heating are
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