Biomedical Engineering Reference
In-Depth Information
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Figure 1.4
An example of covalent surface attachment of a protein molecule via an
activation process.
base residues, especially thymine, can also be the groups of choice though, in
this case, linking may compromise future duplex formation.
A common protocol to bind enzymes, antibodies and molecular receptors to
the substrate is to initially functionalize the surface, followed by a second
reaction(s) which is usually termed 'activation'. In essence, this process simply
allows a convenient, highly reactive 'linker' moiety to be introduced to the
system. The resulting interface is then normally allowed to react in turn with
one of the protein nucleophilic groups mentioned above. The literature is
replete with many examples of this sort of approach and Figure 1.4 provides a
schematic of one strategy. If groups already evident on the device surface are
not used directly, functionalization of surfaces is often achieved with species
such as aminopropyltriethoxysilane (APTES) which reacts with interfacial
hydroxyl groups on whatever substrate they are present. Many other chemical
systems have been employed. One activating configuration that has been used
ubiquitously in the literature is the well-known ethyl(dimethylaminopropyl)
carbodiimide-N-hydroxysuccinimide (EDC-NHS) chemistry (see Figure 1.4).
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1.3.4 Assembled Monolayer Chemistry
The introduction of close-packed monolayers of either membrane-forming
molecules or linking systems for attachment of probes, often following similar
activation to that described above, have been used widely in biosensor devel-
opment. Two very different strategies are employed, the first being the
Langmuir-Blodgett film technique.
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In this experiment, close-packed
monolayers are imposed on a surface in an orchestrated fashion by transferring
lipid or lipid-like (amphiphile) films from the Langmuir trough, under the
correct surface pressure conditions, by a dipping process (Figure 1.5). In
principle, several layers can be deposited in sequence using the dipping
approach. The important advantage offered by this technique is the possibility
to combine artificial lipid membrane configurations directly and in situ with
integral membrane proteins (IMPs). Such membrane systems are, of course,
