Prototyping of microfluidic systems with integrated ... - DTU Nanotech

Chapter 2
Theoretical aspects –
microfluidics and optics
2.1 Introduction
Prototyping of microfluidic system is in many ways a cross-disciplinary
field. Knowledge about physics like fluid dynamics, optics, and solid
state physics is required, along with chemistry – for instance knowledge
about polymers and solvents – and engineering.
While the design of prototypes and the development and refinement
of manufacturing methods is often based on a combination of previous
knowledge combined with intuition and a trial-and-error approach, it is
still crucial to recognise the underlying physical principles and theories
in play in the systems.
Several theoretical issues must be considered when designing and
manufacturing a microfluidic system with integrated optical waveguides.
If chemical reactions, separation, and/or mixing are to take place, it is
vital that the liquid is properly mixed or separated when measurements
are carried out. If, e.g., a liquid is not sufficiently well mixed when an
absorbance or fluorescence measurement is carried out, erroneous results
are likely to occur, since one might measure a more or less diluted part
of the liquid.
When designing a microfluidic network, care must be taken to ensure
that the fluid is led through the system in the proper manner. If the
cross section of the microfluidic channel is suddenly increased, e.g. by
going from a channel to a larger reservoir, the drop in the pressure may
generate bubbles in the system. Also, geometrical considerations are
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