The effect of the latex surface density on dT35 grafting was studied using various latexes. As expected, the greater the cationic charge on the latex surface, the higher the dT35 adsorption through electrostatic interactions, as illustrated in Figure 23. The extrapolation to zero charge provides 0.35 mg/m2 immobilized
Overall charge density (pmol/m2 )
FIG. 23 Influence of the overall charge density of the latexes on the adsorbed and grafted dT35 amounts. (O) immobilized dT35; (•) covalently grafted dT35. (From Ref. 26.)
dT35, slightly higher than the value for nonactivated dT35. In addition, both amine and amidine functions were able to react with the activated dT35 molecules, as denoted by the linear relationship between the amount of grafted dT35 and surface charge density (Fig. 23). The amount of desorbed dT35 was almost constant, revealing that both functions (amine and amidine) exhibited the same reactivity toward the activated ODN. In any case, to target a high grafted amount of activated ODN, high surface charge density is needed.
The influence of a dT35 sequence added as a spacer arm to any ODN sequence results in enhancement of the covalent binding efficiency  and, consequently, the hybridization yield.
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