EFFECT OF CHARGE NATURE ON THE ADSORPTION OF SINGLE-STRANDED-DNA FRAGMENTS ONTO LATEX-PARTICLES

The adsorption of single-stranded DNA fragments (oligonucleotides) ont o latex particles is investigated using a series of polymer latexes ex hibiting various surface charge and group natures (sulfate, amidine, a nd amine). The latexes are prepared using free emulsion polymerization . In this work, we study the adsorption of single labeled oligonucleot ide polythymidylic acid and of a 35-base-bearing fluorescein group (Fl uo-dT(35)) on four latexes to elucidate certain general principles of oligonucleotide adsorption as a function of surface charge nature. Sev eral results are presented in this paper. It was found that the adsorb ed amount of oligonucleotide is strongly dependent on the pH of the me dium and the charge density of positively charged latex particles. Thi s indicates that electrostatic forces play a major role in the adsorpt ion process. The maximal adsorbed amount was found to be lower than th e one calculated from the jamming limit for the random sequential adso rption of nonoverlapping rigid rods adsorbed in two dimensions. Desorp tion of the oligonucleotide was also studied by fluorescence measureme nts, in which both the supernatant and the latex particles were analyz ed using the front face analysis method. In addition, attempts were ma de 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.