Chemistry Reference
In-Depth Information
Technological monolithic approach
Point of
care
R
e
a
l
S
o
l
v
e
d
Sensors/
electonics
Pumping
Metering
Mixing
Incubation
Analytical approach
p
r
o
b
l
e
m
DNA
Clinical
bioanalytical
Sampling &
sample
introduction
W
o
r
l
d
Sample
preparation
Separation
Detection
Environmental
Food
Analytical microsystem
Figure 17.8
Philosophy of the integrated analytical process on analytical microsystems.
(MS) are the most commonly used routes. LIF was the original detection technique and it is the most often
used detection scheme because of its inherent sensitivity [81]. However, the high cost and large size of the
instrumental set-up for LIF has been sometimes incompatible with the concept of
TAS. In addition, tedious
derivatization schemes are needed to use LIF with non-fluorescent compounds. The principal alternative to
LIF detection is ED. The great importance of ED lies in its inherent miniaturization without loss of performance
and its high compatibility with microfabrication techniques. Likewise, it possesses high sensitivity, its
responses are not dependent on the optical path length or sample turbidity and it has low power supply
requirements which are additional advantages. Proof of the predominant role of ED can be easily found in
selected literature [82-84]. Apart from LIF and ED, there are other detection approaches for analytical
microsystems, but from a realistic point of view, they have been developed to a lesser extent [85].
With respect to separation techniques, microchip electrophoresis (MEC) was one of the earliest examples
μ
of
TAS, and it constitutes one of the most representative examples of analytical microsystems [86].
This technology emerged as an important new analytical technique in the early 1990s with the introduction of
the
μ
TAS concept [76] and the seminal work of Manz
et al
. [87]. This new technology was a result of the
marriage of the ability of conventional CE to analyse ultra-small volumes (nl) and microfabrication techniques
perfected in the semiconductor industry to produce very small structures in silicon. Using CE microchips,
analysis times can be reduced to seconds and extremely high separation efficiencies can be achieved. The
easy microfabrication of a network of channels using materials of well-known chemistry, which themselves
have good electroosmotic flows and the possibility of using the electrokinetic phenomena to move fluids, are
among the most important factors to understand the relevance of CE microchips to miniaturization. Since
electrokinetics is easy to apply (only a pair of electrodes are needed), electroosmotic-driven flow (EOF) has
been successfully implemented using different types of materials to manufacture the channels, being glass the
most commonly used. Microfabrication on polymers is faster and cheaper than on glass, so these materials
have great potential for mass production. However, glass chips present the best EOF and the chemical
μ
