Biomedical Engineering Reference
In-Depth Information
materials can in principle also be used for waste water treatment. The application of
chemical sensors is not restricted to single analyte detection within a matrix but can
also be extended to complex mixtures, such as in engine oil degradation sensing
[ 28 - 30 ]. In this case, not only is the application interesting, but it also covers a more
unusual aspect of sensing: the overall changes in a rather complex matrix are
translated into a single sensor response thus yielding a signal that indeed relies on
chemical changes in the matrix, but without actually knowing them in detail. Of
course, parallel detection of several compounds is also possible with MIP-based
sensors: arrays can be constructed for such multicomponent detection and quantifi-
cation that contain between two and a few dozen individual sensors. The data
obtained from such systems have then to be evaluated by chemometric data
analysis, including among other techniques artificial neural networks (ANN) or
principal component analysis (PCA). The following paragraphs shall discuss in
more detail some examples of the above-mentioned MIP applications.
4.1 MIP Sensors in Multicomponent Environments
Usually the detection of environmentally important contaminants faces the
challenges of achieving high sensitivity and selectivity as a consequence of low
analyte concentrations on one hand and complex matrices on the other hand.
Therefore, there is still only a very limited number of chemosensors published for
such applications. These include sensors for: alcohols, esters, ketones, aldehydes,
organic acids, and terpenes from different sources. Their quantitative detection in
the surrounding atmosphere is of importance for environmental, epidemiological,
and toxicological studies [ 45 ], but may also be relevant to process control
applications. An example for the latter case is given by an approach to determine
the lead analytes produced in composting procedures, namely limonene, ethyl
acetate, and aliphatic alcohols, by using an array of six MIP-coated QCM as
transducer [ 11 ]. In such cases relatively high detection limits are an acceptable
characteristic. Each analyte group is addressed by a tailor-made polymer, i.e., a
polystyrene-based material for the aliphatic terpene, polyurethane for the aliphatic
alcohols, and both systems for ethyl acetate.
The respective arrays (for example see Fig. 7 ) operate in the composter environ-
ment for several weeks and continuously monitor the headspace, giving rise to
signals that can be validated by GC-MS. MIPs contribute to the success of these
measurements in two ways: first, they add selectivity to the array, hence allowing
for appreciable detection limits, and second, they do so by providing a matrix that
can be exposed to highly humid environments (up to condensing at 40-45 C) over
several weeks and then be reused. Such a combination of selectivities generated by
both MIPs (that typically yield selectivity factors of 3-10 between closely related
compounds) and chemometry allows one to distinguish between different terpenes
emanating from a variety of natural sources [ 34 ]. The release of terpenes to the
atmosphere has the potential to affect the global radiation balance due to their
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