worm-like coils ( 13). In this model, a long fragment of linear doublehelical DNA behaves as a worm-like chain, whereas a short fragment has DNA adsorption onto polypyrrole (PPy) powder, a colloidal a rodlike behavior (13 ).
silica sol, and three polypyrrole-silica nanocomposite particles
Recently, we reported a study of DNA adsorption onto a series of PPy (untreated and amine-or carboxylic acid-functionalized) was inpowders. The extent of DNA adsorption was found to be in the range of vestigated at neutral pH using sodium phosphate buffer. The ex-3-13 mg/g, depending on the solution pH, electrolyte concentration, buffer tent of DNA adsorption was found to be 32 and 22 mg/g for the type, and the nature of the dopant anions incorporated into the cationic PPy aminated silica sol and aminated PPy-silica particles respectively, chains ( 14). It was shown that DNA adsorption increased with increasing and 6.5 mg/g for the carboxylated particles. DNA adsorption onto acidity (from pH 9 down to pH 5), and increasing salt concentration ( C s ) the unfunctionalized PPy-silica particles occurs to a lesser extent, of the medium. These results were in general agreement with the adsorption whereas no adsorption was detected for the colloidal silica sol. of polyelectrolytes onto hydrophobic surfaces (15).
Our results suggest that DNA adsorption is mainly governed by
Maeda and Armes ( 16) have shown that the polymerization of pyrrole in the presence of ultrafine aqueous silica sols can, under appropriate condi-electrostatic and hydrophobic interactions. DNA is adsorbed onto tions, lead directly to the formation of PPy-silica nanocomposite particles polypyrrole chloride bulk powder and also onto the aminated (see Fig. 2). These particles are relatively monodisperse and have an un-PPy-silica particles, which both have cationic binding sites. The usual ''raspberry'' morphology. Aqueous dispersions exhibit good colloidal silica sol and the unfunctionalized PPy-silica particles both posstability ( 16) and the dried nanocomposites have relatively high specific sess a net negative surface charge at this pH, which probably surface areas (17) compared to PPy powders. Indeed, BET measurements accounts for the zero or very low adsorbed amounts of DNA on indicate that conducting polymer-silica raspberry particles can have sig- these substrates. DNA adsorption onto the carboxylated PPy-silnificant microporosity (17). ica particles may be enhanced by hydrogen bonding relative to the X-ray photoelectron spectroscopy studies (18) confirmed the presence unfunctionalized polypyrrole-silica particles.