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

2 Introduction
that well-established methods were available from the semiconductor
industry, where the miniaturisation of integrated circuits had been an
ongoing process since the 1970s. In the last decade, however, alternative
materials have been entering the µTAS scene, since both the cost and
the lack of compatibility with many analytes and chemical environments
make silicon a poor material choice. The interest in polymers has
increased considerably, since a large variety of polymers with a diversity
of properties (chemical, optical, mechanical etc.) is available at a
cost considerably lower than that of silicon. Also for industrial scale
production, polymers are processable with traditional low-cost methods
like injection molding, which are orders of magnitude cheaper than the
clean room processes used when making silicon structures.
The ongoing miniaturisation in consumer electronics further increases
the urge to miniaturise simple analytical systems for a number of reasons.
An increased focus on and demand for the so-called point-of-care
testing systems has evolved in recent years. Medical treatment can be
improved if samples can be taken and analysed on-site, rather than
taken to a laboratory. Since the computing power necessary for making
even advanced data analysis is present today in a standard laptop
computer, or even in embedded systems in hand-held analytical devices,
the drive to similarly miniaturise the fluidic parts of a system is present.
Miniaturising also decreases the amount of analyte and reagents needed
to perform a given analysis, thus reducing the cost and environmental
effects when disposing of the sample.
1.1 Downscaling
The question that one inevitably poses when looking at the rapid and
constant miniaturisation of microfluidic systems, is: “When is it going
to end?”
A number of very simple practical matters set limits in many areas
of the miniaturisation. The dimensions of the human hand has set a
limitation to the shrinking size of e.g. cellular phones, since the buttons
must have a size comparable to the fingertip of the user for the device
to work as intended.
In microfluidics, many applications can theoretically be downscaled
to nanofluidics, looking at transport of single water molecules through
carbon nanotubes, or similar. Here, the limit to the downscaling is the
molecular scale. For many medical applications, however, the limiting