Effect of charge nature on the adsorption of single-stranded DNA fragments onto latex particles

The adsorption of single-stranded DNA fragments (oligonucleotides) onto latex particles is investigated using a series of polymer latexes exhibiting various surface charge and group natures (sulfate, amidine, and amine). The latexes are prepared using free emulsion polymerization. In this work, we study the adsorption of single labeled oligonucleotide polythymidylic acid and of a 35-base-bearing fluorescein group (Fluo-dT(35)) on four latexes to elucidate certain general principles of oligonucleotide adsorption as a function of surface charge nature. Several results are presented in this paper. It was found that the adsorbed amount of oligonucleotide is strongly dependent on the pH of the medium and the charge density of positively charged latex particles. This indicates that electrostatic forces play a major role in the adsorption process. The maximal adsorbed amount was found to be lower than the one calculated from the jamming limit for the random sequential adsorption of nonoverlapping rigid rods adsorbed in two dimensions. Desorption of the oligonucleotide was also studied by fluorescence measurements, in which both the supernatant and the latex particles were analyzed using the front face analysis method. In addition, attempts were made to correlate the maximum fluorescence emission intensity using the front face analysis with the amount of oligonucleotides adsorbed onto latex particles. (C) 1998 Academic Press.