Microfluidics for Biologists Fundamentals and Applications

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and thus promotes low cost clinical diagnostics which can be of immense utility in
resource poor settings. Various advantages that such devices offer are reduced
detection time, increased sensitivity, greater control of molecular interactions,
cost efficiency, reduced chemical wastage, lesser human intervention etc. With a
purpose of exploring various dimensions of microfluidics in clinical diagnostics,
this chapter summarizes various aspects of the field of point of care diagnostic
devices including their fabrication technologies like Laser micro-machining,
lithography and MRDI process for making micro-channels/micro-valves; micro-
fluidic systems and its various fluid handling modules like micro-mixers, micro-
pump, micro-valve and micro-cantilevers etc. various applications of micro-fluidics
like electrophoresis (gel electrophoresis, capillary electrophoresis and surface elec-
trophoresis), dielectrophoresis, polymerase chain reaction (PCR) and gene delivery
and further various sensing and detection techniques like electrochemical sensing,
optical sensing, mass based sensing and surface plasmon resonance (SPR)
sensing etc.


2 Basic Fabrication Techniques


In this section we would like to discuss the various fabrication techniques that are
normally used for micro-fabrication of high aspect ratio micro-channels.


2.1 LASER


The term LASER is an acronym for Light Amplification by Stimulated Emission of
Radiation. Laser devices produce intense light beams which are monochromatic,
coherent, and highly collimated. The wavelength of laser light is monochromatic
and all photons are coherent. Laser beams show very low divergence and can travel
over great distances, can be focused to a very small spot with high intensity and find
a variety of applications in different fields.
Atoms possess energies only in particular discreet energy levels although when
in bulk there may be a bulk behaviour of the orbital energies. The electrons within
these atoms are naturally present in their ground state and they go to higher energy
levels when excited through light beams of an external source. This process is
known as absorption. After a short duration of time is lapsed the electrons returns
back to their initial ground states and in the process the atom emits a photon. This
process is known as spontaneous emission. In a traditional light source both
absorption and emission occur together. If an outside photon having precisely the
amount of energy needed for spontaneous emission is struck on the excited atoms,
this external photon is increased to two photons one provided by the excited atom.
Both released photons have the exact same phase. This process is known as
stimulated emission and it is a fundamental process for the operation of a laser


2 Microfluidics Overview 35

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