Biochips – fundamentals and applications - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 367

Three “M”s, i.e. multiplicity, miniaturization, and microelectronics, are often used
to describe MEMS technology. This defi nitely presents the prominent features of an
LOC. Miniaturization refers to micron and/or nanoscale devices. Multiplicity refers to
the batch fabrication on the scale of semiconductor manufacturing. This characteristic
of LOC enables production of thousands or millions of identical devices concurrently.
Microelectronics is what ties the other two “M”s together. LOC devices owe a lot to
microelectronics fabrication R&D. However, without the integration of mechanical
and electronic functions found in LOCs, the devices would have no capability to merge
functions of sensors, actuators, and logic. Similarly, the information generated within
LOCs is meaningless without some way of processing it rapidly and reproducibly. For
both MEMS and LOCs, the relative positioning of electronics and mechanics is unim-
portant. There is no reason why electronics must be contained on the same chip as the
other functions, although this is possible in both cases. Integration of an LOC involves
critical, challenging, packaging issues including microfl uidic interconnects (connect-
ing device to device and interfacing macrocomponent to microdevice). The functions
of packaging are to protect the devices from the environment and also protect the envi-
ronment from the device operation. Sealing techniques, hermeticity measurements, and
mechanical protection are used to ensure structural integrity and dimensional stability,
thermal and optical isolation, and chemical and biological protection. These techniques
are discussed in the literature [168].
11.5.4 Applications
LOCs are capable of conducting various types of chemical and cellular analysis, sep-
arations and reactions. In the last couple of years, LOC has been one of the fastest
growing areas of microfabrication and nanotechnology development, integrating many
technologies to develop applications in a wide range of disciplines including genetic
analysis, disease diagnosis, culturing and manipulating cells, drug discovery, and mate-
rials chemistry. The LOC has enabled many types of sensor, actuator, and system to be
reduced in size by orders of magnitude, while often even improving sensor perform-
ance (e.g. inertial sensors, optical switch arrays, biochemical analysis systems, etc.). It
has demonstrated great potential in commercialization.
11.5.4.1 Cell sorting system
Cell sorting and counting are important methods for cell detection. Early detec-
tion of malignant cells is critical to the successful treatment of cancers. The diffi -
culty in detecting these cells arises from the subtle onset of the disease in a single
cell embedded in a host organ comprising billions of cells. Flow cytometry (FCM) is
a very effective technique for tackling this challenge [174]. However, conventional
fl ow cytometers tend to be large, expensive bench top systems that require specially
trained personnel for sample tagging and instrument operation. A cytometry microsys-
tem based on microfl uidics could be a relatively cheap and portable cell interroga-
tion tool with far-reaching applications in point of care diagnosis. Dielectrophoretic