[Show abstract][Hide abstract] ABSTRACT: DNA adsorption onto polypyrrole (PPy) powder particles has been monitored, ex situ, by X-ray photoelectron spectroscopy (XPS) technique. DNA adsorption isotherms were determined by the quantitative analysis of the XPS spectra, and by plotting the X/N atomic ratios (X = C, O, Cl, P and Na) versus DNA equilibrium concentration. All XPS isotherms are of high affinity type, showing high adsorption amounts at low DNA concentrations in the suspension. Moreover, inspection of the C1s peak structure of the PPy–DNA complex revealed that it gradually gets wider and less tailing as DNA adsorbs, clearly showing the DNA contribution to the peak enlargement. In addition, the changes observed in the Cl2p structure bring a strong supporting evidence of anion-exchange mechanism that takes place at initial stages of the interaction. Actually, the polypyrrole backbone loses part of its residual chlorides as the first DNA fragments adsorb and neutralize the PPy positive charges at the interface. Moreover, at relatively high amounts of adsorbed DNA, the PPy surface becomes screened necessitating thus that sodium cations co-adsorb in order to compensate for the excess of DNA negative charges. As a consequence of such screening of the PPy surface, DNA adsorption results in a positive spectral shift of all peaks of approximately 2.0 eV, a value that leads to the conclusion that DNA partially covers the PPy.
[Show abstract][Hide abstract] ABSTRACT: The interest of high frequency impedance measurements performed on decanted solids was demonstrated for the in situ investigation of DNA adsorption onto polypyrrole (PPy). The dielectric method was first applied to distinguish between polymers containing different dopant and to monitor their ion-exchange occurring when PPy was contacting a phosphate buffer solution. Results were compared to those obtained by X-ray photoelectron spectroscopy (XPS) and ion-exchange chromatography. Afterwards, the effects of DNA adsorption were investigated in 0.01 M phosphate buffer at pH 7. A significant decrease in the dielectric parameters was observed upon the adsorption, as a result of the coverage of the conductive PPy by an insulating layer of DNA, while maintaining, however, the mobility of doping anions in the bulk of the polymer. Irreversibility of the adsorption process was assessed. Some conformational changes of the adsorbed DNA have been suspected to occur during the deposition of increasing amounts of DNA.
Full-text · Article · Jan 2000 · Sensors and Actuators B Chemical
[Show abstract][Hide abstract] ABSTRACT: Adsorption of human serum albumin (HSA) onto polypyrrole powder and polypyrrole-silica nanocomposite is investigated at pH 7.4 and RT using UV spectroscopy. the nanocomposite is more effective than the powder in adsorbing HSA (147 and 63 mg/g, respectively). XPS was used to detect characteristic features of the adsorbed HSA and to construct adsorption isotherms. These latter were in fair agreement with those obtained via UV. Polypyrrole-silica is adsorptive towards HSA at pH 7.4 by contrast with the quasi-zero adsorption previously obtained with the DNA adsorbate (Saoudi et al., J. Colloid Interface Sci. 1997).
[Show abstract][Hide abstract] ABSTRACT: DNA adsorption onto polypyrrole (PPy) powder, a colloidal silica sol, and three polypyrrole-silica nanocomposite particles (untreated and amine- or carboxylic acid-functionalized) was investigated at neutral pH using sodium phosphate buffer. The extent of DNA adsorption was found to be 32 and 22 mg/g for the aminated silica sol and aminated PPy-silica particles respectively, and 6.5 mg/g for the carboxylated particles. DNA adsorption onto the unfunctionalized PPy-silica particles occurs to a lesser extent, whereas no adsorption was detected for the colloidal silica sol. Our results suggest that DNA adsorption is mainly governed by electrostatic and hydrophobic interactions. DNA is adsorbed onto polypyrrole chloride bulk powder and also onto the aminated PPy-silica particles, which both have cationic binding sites. The silica sol and the unfunctionalized PPy-silica particles both possess a net negative surface charge at this pH, which probably accounts for the zero or very low adsorbed amounts of DNA on these substrates. DNA adsorption onto the carboxylated PPy-silica particles may be enhanced by hydrogen bonding relative to the unfunctionalized polypyrrole-silica particles.
No preview · Article · Sep 1997 · Journal of Colloid and Interface Science
[Show abstract][Hide abstract] ABSTRACT: Deoxyribonucleic acid (DNA) adsorption onto chemically synthesized polypyrrole powders was investigated as a function of pH, buffer nature, ionic strength and substrate nature. DNA adsorption was found to be in the range of 0.13–0.55 mg m−2 for the conditions under investigation. Strong DNA adsorption was obtained at low pH and high ionic strength. The decreasing order of adsorption as a function of the native dopant was nitrate, chloride>sulfate. The isotherms were found to be of the Langmuir type or sigmoid, depending on the combination of (at least) substrate and buffer natures. Affinity constants determined using Scatchard and Hill plots were found to be as high as 106 M−1.
No preview · Article · Mar 1997 · Synthetic Metals
[Show abstract][Hide abstract] ABSTRACT: This paper reports on die study of adsorption of PMMA, a conventional homopolymer, and DNA onto some conducting polypyrroles (PPys) using a variety of techniques. PMMA adsorption was monitored using X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectroscopy (ToFSIMS). XPS and ToFSIMS permit to determine the surface composition of PPy surfaces following PMMA adsorption from various solvents, at different concentrations and on three variously doped PPys. Both techniques show that acid-base interactions are important and may govern PMMA adsorption. In addition to these spectroscopies we have used inverse gas chromatography (IGC) to monitor the surface thermodynamic properties of the coated PPy powders and found a solvent effect on the morphology of PMMA coatings. An attempt to check if the same phenomenon is observed on flat surfaces was performed using atomic force microscopy (AFM). In the case of the adsorption of DNA (polyanionic macromolecule) onto PPy (positively charged polymer chains) using the depletion method in combination with UV spectroscopy, we found that adsorption is one to two orders of magnitude higher than that of conventional polymers onto classical filters. The pH effect was found to be of limited influence on the adsorption isotherms contrary to the effect of PPy dopant which was found to be the major factor governing DNA adsorption.