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Note that Eq. (6.6) predicts the binding rate coefficient values presented in Table 6.4 reasonably well. The high exponent dependence of k on Df once again indicates that the k value is very sensitive to the degree of heterogeneity that exists on the BIACORE surface. Note that the range of the fractal dimension presented in Fig. 6.11 and Table 6.4 is rather narrow. More data points are required over a wider range of Df values to further establish Eq. (6.6). As indicated earlier, the data analysis in itself does not provide any evidence for surface roughness or heterogeneity, so the assumed existence of surface roughness or heterogeneity may not be correct.

Richalet-Secordel et al. (1997) also utilized the BIACORE biosensor to analyze the binding of mFab 20.5.3 in solution to biotinylated gp32 peptide (598 RU). Once again, different flow rates were used. Figure 6.12 shows that for the range of 2 to 100 ¿ul/min flow rates a single-fractal analysis is adequate to describe the binding kinetics. Table 6.4b shows the values of k and Df for the flow rates used. For the different flow rates presented in Table 6.4, the binding rate coefficient may be represented by k = (2.331 ±0.541)D°-2UO±l172°. (6.7)

Ingersoll and Bright (1997) utilized fluorescence to probe biosensor interfacial dynamics. These authors immobilized active dansylated IgG at the

Time, sec Time, sec

FIGURE 6.12 Influence of different flow rates (in /il/min) on the binding of mFab 20.5.3 in solution to biotinylated gp32 peptide immobilized on a BIACORE biosensor (Richalet-Secordel et al, 1997). (a) 2; (b) 5; (c) 10; (d) 25; (e) 50; (f) 100.

Time, sec Time, sec

FIGURE 6.12 Influence of different flow rates (in /il/min) on the binding of mFab 20.5.3 in solution to biotinylated gp32 peptide immobilized on a BIACORE biosensor (Richalet-Secordel et al, 1997). (a) 2; (b) 5; (c) 10; (d) 25; (e) 50; (f) 100.

interface. They controlled the active IgG by mixing active anti-BSA IgG with the Fc segment of the same IgG. Figure 6.13 shows the curves obtained using Eq. (6.2a) for the binding of 1 /¿M BSA in solution to the anti-BSA-protein G fused to the biosensor surface for three different IgG/Fc ratios. A single-fractal analysis is again sufficient to adequately model the binding kinetics.

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