In this study, the adsorption of single-stranded oligodeoxyribonucleotides (ODN) onto well-characterized polymer latex particles has been investigated. At first, the case of poly(thymidylic acid) (dT35) was thoroughly examined as a function of pH and ionic strength in the presence of cationic polystyrene colloids prepared by emulsifier-free copolymerization of styrene and vinylbenzylamine hydrochloride. Due to the polyelectrolyte character of the oligodeoxyribonucleotides (which are negatively charged) and the positive charges of the particles, strong adsorption was clearly noticed together with a high affinity; in addition, a decrease in the maximal adsorption was observed upon raising the pH. These adsorption phenomena corroborate that electrostatic forces play a major role in the adsorption process; however the contribution of hydrophobic forces was also evidenced using the various adsorption isotherms at various pHs and extrapolating these results to zero surface charge density (σ = 0) and to zero zeta-potential (ζ = 0) of the latex particles. Moreover, the effect of poly(thymidylic acid) chain length on the maximum adsorbed amount on the latex particles was also investigated, providing information on the state of conformation of the ODN at the particle surface; it was suggested that the ODN adsorbs in a flat conformation. Such a behavior can be extended regardless of ODN nature so long as the support was oppositely charged. Finally, an attempt was made to predict the adsorption behavior of single-stranded ODN using the general approach of Hesselink for polyelectrolytes.

The activation of various synthetic oligodeoxyribonucleotides (ODNs), bearing a hexamethylamine arm at their 5 0 -end, with the 2,4-phenylenediisothiocyanate (PDC) was studied. The activation reaction had to be performed within 40 min, because of competitive hydrolysis of the isothiocyanate functions. ODN modifications were then characterized by different analytical methods i.e. gel capillary electrophoresis, Matrix-Assisted Laser Desorption-Ionization-Time of Flight (MALDI-TOF) mass spectrometry. Moreover, activation of the amine groups of the nucleic bases was evidenced through the chemical analysis of the enzymatic-digested conjugate (PDC-ODN) by reverse phase HPLC. Preliminary results on the covalent grafting of activated ODN molecules onto the aminated latex particles showed that the amount of grafted ODNs was directly related to the number of potential grafting sites on the nucleic acid probe (primary amine group of hexamethyl arm and amine functions of the nucleic bases).