Effect of Ionic Strength

According to the polyelectrolyte character of oligonucleotides, the effect of ionic strength should not be neglected in the understanding of the driven forces involved in the adsorption process. It is imperative when investigating the effect of salt to preserve the colloidal stability of the latex particles. The first study on the influence of ionic strength has been dedicated to the ODN adsorption onto

FIG. 11 Effect of pH on the maximal adsorbed dT35 onto bare and precoated latex particles (by adsorbing a small amount of Triton-X405) as a function of pH at 20°C and 10-3 M ionic strength. (From Ref. 11.)

FIG. 11 Effect of pH on the maximal adsorbed dT35 onto bare and precoated latex particles (by adsorbing a small amount of Triton-X405) as a function of pH at 20°C and 10-3 M ionic strength. (From Ref. 11.)

sulfate polystyrene latexes. Surprisingly, the salinity has a marginal effect on the ODN adsorbed amount [10].

On the contrary, the increase in salt concentration has a nonmarked effect while using cationic latexes. A small increase in ODN adsorption was observed for bare cationic particles, whereas surface ODN contents decreased in the presence of the interfacial nonionic surfactant layer (Fig. 12). The behavior observed has been mainly attributed to the reduction of attractive electrostatic interactions. In addition, increasing the salt concentration may enhance the contribution of hydrophobic forces [13].

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