Effect of Ionic Strength on the Desorption of Oligonucleotide

To reduce the attractive electrostatic interactions between both species (ODN and cationic latex particles), the influence of salt concentration was investigated. The effect of ionic strength on the desorption process is reported in Fig. 17, in l

FIG. 16 Residual adsorbed dT35 onto bare latex particles as a function of pH. Adsorption was performed on bare latex particles. The desorption was carried out after two washes using buffer (at a given pH, 10-2 M ionic strength, and 1% Triton X-405). (From Ref. 11.)

102 101 10° NaCl Concentration (mcl L")

FIG. 17 Residual adsorbed dT35 onto bare latex particles as a function of ionic strength. Adsorption was performed on bare latex particles with Ns = 1.0 mg m- at pH 5 and 10-M ionic strength. The desorption was carried out after two washes using buffer (at various ionic strengths, pH 10, and 1% Triton X-405). (From Ref. 11.)

102 101 10° NaCl Concentration (mcl L")

FIG. 17 Residual adsorbed dT35 onto bare latex particles as a function of ionic strength. Adsorption was performed on bare latex particles with Ns = 1.0 mg m- at pH 5 and 10-M ionic strength. The desorption was carried out after two washes using buffer (at various ionic strengths, pH 10, and 1% Triton X-405). (From Ref. 11.)

which the residual adsorbed amount of preadsorbed ODN (at pH 5) is reported as a function of added NaCl concentration (buffer pH 10, 1 wt % Triton X-405). The desorption was found to be dramatically enhanced at high salt content (after two washes only). The screening effect of the surface charges (due to the salt) and the hydrophilic (because of the surfactant layer) character of latex surface enhance the repelling process of the ODNs. Then the combination of pH, ionic strength, and competitive agent (i.e., noncharged surfactant) leads to good control of the desorption phenomena. In fact, the pH and ionic strength reduce the attractive forces, whereas the surfactant acts as a competitor and as an energy barrier affecting the adsorption of free ODN.

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