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Figure 15.2 Depiction of the binding site heterogeneity of a molecular imprinted polymer.
small fraction of the functional monomers form productive binding sites. Instead the
majority of functional monomers are randomly incorporated into the walls of the
channel or are inaccessible within the polymer matrix.
The binding affinities within a single MIP are similarly heterogeneous and span
the entire range from low to high affinity. The typical binding affinity distribution
observed in an MIP is shown in Figure 15.3 (Umpleby et al. 2000, 2001). The dis-
tribution is strongly weighted toward the nonspecific low-affinity sites. Thus, the
average binding affinities of MIPs are much lower than antibodies and aptamers
(Houk et al. 2003). However, the binding site distribution does asymptotically tail
out into the high-affinity region (Fig. 15.3). Thus, there is a small but accessible
subset of binding sites with high affinity and selectivity. This asymmetric distribution
helps to explain the strong concentration dependence of the binding properties of
MIPs. At higher analyte concentrations, both the low- and high-affinity sites are
Figure 15.3 Typical heterogeneous distribution of binding site affinities found in molecular
imprinted polymers compared with the homogenous distribution of a typical monoclonal anti-
body. Reprinted from Umpleby et al. (2001). Copyright 2001 American Chemical Society.
