Biomedical Engineering Reference
In-Depth Information
multidimensional data - extract useful information from the data arrays and suppress
unwanted interferences. Note that the application of sophisticated signal process-
ing methods cannot be a panacea: if there is no relevant information in a sensor array
response there is no way to get it, as in the case of a black cat in a dark room.
The problem of multianalyte analysis is of high importance in different methods
of analytical chemistry. The measurements with sensor arrays are not an exception;
they are always complicated by multicomponent calibrations, as the number of these
calibrations, even if defi ned in accordance with the modern principles of experimental
design, increases exponentially with the increase in the number of analytes.
In some cases the exact data on numerous analyte concentrations are of less impor-
tance. Sample classifi cation according to some property or set of properties is often
required instead. Thus, a “chemical image” or “fi ngerprint” of a sample could be used
as an integral characteristic, which contains information on various critical parame-
ters. The properly trained (calibrated) multisensor system, often referred as “electronic
tongue”, complemented with pattern recognition tools, is capable of distinguishing
between “good” and “bad” samples or even allowing wider classifi cation [14]. Design of
a multisensor system for a certain application is a challenge, as mechanism(s) of sensor
responses may be unclear in complex media, which signifi cantly hinders the develop-
ment of such systems. The electronic tongues, comprised of non-specifi c cross-sensitive
sensors, have been applied for analysis of various types of samples, including pharma-
ceutical formulations [106]. However, the proposed concept of cross-sensitivity and the
declared advantages of non-specifi c sensors are often disputed by the scientifi c commu-
nity. There is still much work required in order to convert the electronic tongue approach
to a recognized analytical method.
4.6 FUTURE PROSPECTS AND CONCLUSIONS
Ion-selective electrode research for biomedical analysis is no longer the relatively nar-
row, focused fi eld of identifying and synthesizing ionophores for improved selectiv-
ity and the integration of ion-selective electrodes into clinical analyzers and portable
instruments. These efforts have matured now to such an extent that they can teach val-
uable lessons to other chemical sensing fi elds that are just emerging technologies.
Ion-selective electrodes are now well understood in terms of the underlying theory,
and this has made it possible for new sensing principles to emerge that make use of the
thousands of chemical receptors originally developed for ion-selective electrodes. One
is the fi eld of optical sensors, which has not been discussed here because it is outside
the focus of this chapter. Such so-called bulk optodes do not require electrical con-
nectivity between the sensing and detection unit and are therefore more easily brought
into various shapes and sizes, including particle formats, which suit the need of mod-
ern chemical analysis.
Electrochemical sensors, however, currently share one key advantage: an excitation
signal may be imposed that can trigger a sensing reaction, and the energy required for
an otherwise thermodynamically unfavorable extraction and/or binding process can be
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