Selective adsorption behaviors of proteins on polypyrrole-based adsorbents

In this study, polypyrrole-based adsorbents were prepared by doping polypyrrole (PPy) with chloride (PPyCl), dodecyl sulfate (PPyDS) or octadecyl sulfate (PPyOS) and by aminating PPy with aminopropyl-triethoxy-silane (N-PPy). The adsorbents were investigated for their behaviors in selective adsorption of bovine serum albumin (BSA) and lysozyme (LSZ) in aqueous solutions under different pH conditions. Zeta potential analyses, Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared adsorbents and to examine the specific interactions that may exist between the proteins and the adsorbents in the adsorption process. It was found that at pH around 5, a great amount of BSA, but nearly no LSZ at all, was adsorbed on PPyCl adsorbent. In contrast, a significant amount of LSZ was adsorbed on PPyDS or PPyOS adsorbent, but almost no BSA was adsorbed by these two types of adsorbents at pH about 10. N-PPy adsorbent, however, did not show good selectivity for the adsorption of BSA or LSZ in the pH range of 2–10 studied. The observed experimental phenomena can be explained by the various adsorption mechanisms, such as electrostatic interaction, hydrophobic interaction and surface complex formation. The work indicates that polypyrrole-based adsorbents may have a great potential in selective adsorption for enhancing or inhibiting a targeted protein on their surfaces for various applications.