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FIGURE 8.15 Influence of an increasing forward binding rate coefficient, fef, on the normalized antigen concentration in solution near the surface, cs/c0, when nonspecific binding is present for (a) a = 0.01 and (c) a = 0.1, and on the amount of antigen specifically bound to the antibody on the biosensor surface, TL/c0, for a second-order reaction for (b) a = 0.01, and (d) a = 0.1.

highest f! ( = 0.025) specific binding curve exhibits the highest rate of binding and the highest amount of antigen in solution specifically bound to the antibody immobilized on the surface. After about 120 sec, the optimum value of/? is 0.005. This (! value leads to the highest rate of specific binding and the maximum amount of antigen in solution specifically bound to the antibody immobilized on the surface. It seems, once again, that the optimum value of /S depends on the time interval of measurement. Figure 8.15c shows that for an a value of 0.1 an increase in leads to a decrease in the cs/c0 value. Figure 8.15d exhibits interesting behavior in that an increase in the binding rate coefficient leads to a decrease in the r^g/co value. Apparently, in this case an increase in the fi value in the forward binding rate coefficient leads to an increase in the Damkohler number (increase in the external mass transfer limitations), which leads to a decrease in the T\Jcq values. Similar behavior was reported by Sadana and Sii (1991), as previously indicated for an increasing forward binding rate coefficient when nonspecific binding was absent (a = 0).

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