Influence of Adsorption on Chemical Grafting Efficiency

The adsorption of ODN during chemical grafting experiences appears to be vital in order to bring the ODN into contact with the surface of the latex particles. A priori, the conditions facilitating adsorption and covalent grafting are incompatible. In fact, the adsorption is more efficient under high cationic charge densities (protonated amines at acidic pH) whereas grafting is better facilitated when the amine functions are no longer protected. Thus, a compromise has to be found between these different operating conditions.

As previously reported, adsorption of dT35 is a very rapid process. Similarly, covalent grafting was shown to be very fast presumably because of multisite grafting. Meanwhile, the amount of overall immobilized activated dT35 increased slightly with time as shown in Fig. 21. The covalent grafted amounts were determined after desorption investigations as discussed above. The amount of

immobilized oligonucleotide decreased upon increasing pH (from 8 to 11), due to the vanishing of the cationic surface charges on the particles (Fig. 22). However, this decrease is less marked than in the case of the adsorption process. The behavior revealed principally the contribution of electrostatic interaction to the chemical grafting process.

FIG. 21 Kinetics of adsorption and grafting of dT35 on latex particles in 10 mM sodium borate buffer, pH 9.3. (O) immobilized dT35; (•) covalently grafted dT35. (From Ref. 26.)
FIG. 22 Influence of pH on the adsorption and grafting of dT35 onto latex particles. (O) immobilized dT35; (•) covalently grafted dT35. (From Ref. 26.)

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