Biomedical Engineering Reference
In-Depth Information
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Figure 1.1
Schematic of typical components of biosensor architecture.
oxide sensor which responds to gases such as carbon monoxide.
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In contrast,
biosensors are composed of a union between a transducer and biological/
biochemical receptor. A schematic of the structure including transduction types
is depicted in Figure 1.1. Note that the probe can consist of a variety of
biological entities ranging from antibodies to live biological cells Given that
nucleic acids and proteins are chemicals, as are the targets that cells as probes
are designed to detect, it is clear that the distinction between chemical- and
biosensors is artificial.
Crucial aspects of biosensor technology are the nature of the response of the
device with respect to time and whether ancillary chemistry is required in
addition to the basic probe in order to achieve a signal. With respect to the
former point, there are sensor specialists who take the view that such a device
must respond to its analyte in real time. Conversely, the field is often
considered to include 'one-test' disposable structures where there is no attempt
to conduct a measurement over a period of time, except in a repeated dipstick
fashion. The ubiquitous pregnancy and glucose test strips that are widely
commercially available constitute examples of this approach to biodetection.
The use of an adjunct chemical in addition to the receptor to achieve a
transducer signal is often termed tagging or labeling. An example of this
strategy is the use of dyes in conjunction with nucleic acid probes in order to
produce fluorescent signals.
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In certain cases, there is insucient intrinsic
fluorescence in nucleic acid molecular probes to allow the direct possibility of
detection. The same is true for electrochemical methods where organometallic
complexes (of Ru) have to be employed for work with nucleic acids in order to
detect redox chemistry. Technology where such an approach is avoided is called
'label-free detection' and is often regarded to be attractive in view of the fact
that sensor fabrication becomes a somewhat simpler process.
Additional important technical factors are the possibilities for incorporation
of the device in flow-through automation, sensor miniaturization and
prevention of non-specific adsorption. Such automation involving standalone
systems avoids time-consuming personal intervention and allows rapid data
collection and validation. Microfluidic systems offer speed and saving of
reagent costs. Non-specific adsorption of unwanted components on the device
surface poses something of an Achilles' heel for biosensor technology. The
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