Biomedical Engineering Reference
In-Depth Information
N
N
O
O
O
O
O
O
N
F
F
F
F
S
S
NH
2
NH
S
NH
F
F
F
F
O
F
O
F
HN
HN
O
O
O
O
dansylamine
N
d
n
4
t
3
n
g
|
1
I
II
dansylamine, Et
3
N
DMF, rt, overnight
PFP/OTS
PhMe, rt, 60 min
Cleaned quartz
Si
Si
Si
Si
Si
Si
Si
Si
O
O
O
O
O
O
OH
OH
OH
OH
OO
Quartz
O
O
OO
Quartz
OO
Quartz
PFP/OTS mixed SAM
Dansylamine-functionalized
PFP/OTS mixed SAM
Figure 1.7
Example bifunctional trichlorosilane adlayer on quartz surface with short
chain diluent in place to avoid probe crowding.
(Reprinted by kind permission of the Royal Society of Chemistry.)
d
n
3
.
non-specific adsorption can also be minimized through the use of oligoethylene-
based linkers rather than simple alkyl chains.
33
This is an extension of bio-
materials technology where polyethylene glycol polymer has been known for
many years to enhance the biocompatibility of implants.
1.3.5 The Molecularly Imprinted Polymer
Although not strictly an immobilization technique, we mention for convenience
at this point the molecular imprinted polymer (MIP).
34
This approach bears a
resemblance to the entrapment methodology outlined previously. In MIP
technology, created originally by Mosbach and co-workers,
35
a particular
target molecule is surrounded chemically by a deliberate polymerization
process in order to produce a 'mimicked' biochemical three-dimensional
matrix. The final step in the whole process is the washing out of the target
molecule leaving a cavity ostensibly analogous to that for antigenic species in
antibodies (Figure 1.8). Presumably the cavity is capable of selectively binding
the target molecule via a variety of chemical forces such hydrogen bonds and
van der Waals forces orchestrated in a three-dimensional configuration. The
technique has been used in combination with several types of device, although
the instigated selectivity often appears modest. It is generally the view that an
element of 'collapse' of the cavity is responsible for the reduction of selectivity.
However, this is an active research field and no doubt considerable effort will be
made to enhance selectivity with respect to MIP technology. One such
approach is that of the notion of 'clonal selection' which has been employed
highly successfully in nucleic acid and protein microarray technology. In this
scenario no attempt is made to design a particular cavity. Instead a large array
of variable cavity polymers is deposited onto a substrate and all are allowed to
interact with a particular analyte. As for the aforementioned biochemical
