Time of flight-secondary ion mass spectrometry analysis of protein adsorption on a polyvinylidene difluoride surface modified by ion irradiation

Abstract

We investigated the effects of nanoscopic surface modification of polyvinylidene difluoride (PVDF) and low-density polyethylene (LDPE) by plasma-based ion implantation on protein adsorption with time of flight-secondary ion mass spectrometry (ToF-SIMS) analysis. The chemical composition of the LDPE and PVDF surfaces was changed by ion irradiation. In particular, irradiation substantially decreased the number of CH and CF bonds on the PVDF surface, but only slightly decreased that of CH bonds for LDPE. These decreases may reflect a higher hydrogen recombination rate of the LDPE than the PVDF surface. An increase in oxygen was observed on both the LDPE and PVDF surfaces following ion irradiation, but was saturated after irradiation of 1×1015cm−2 on the PVDF surface. The hydrophilicity of the ion-irradiated LDPE surface was promoted with an increase of the total ion fluence. Ion irradiation also changed the surface properties of PVDF to become more hydrophilic, but the variation did not correlate with the total ion fluence presumably due to the presence of fluorine atoms and the saturation of oxidation. Both bovine serum albumin (BSA) and collagen adsorption were suppressed on the LDPE surface by ion irradiation, which may have resulted from a decrease of the hydrophobic interaction. By contrast, ion irradiation increased protein adsorption on the PVDF surface, and BSA was adsorbed more than collagen, whereas there was no difference in the adsorption between BSA and collagen on the ion-irradiated LDPE surface. Moreover, the adsorption of BSA decreased on the oxygen- and fluorine-rich PVDF surface. These results indicate that the nanoscopic composition changes on the PVDF surface affect the adsorption behavior of BSA. Specifically, ferroelectric property on the PVDF surface was changed by ion irradiation and the nanoscopic change in polarity presumably affected the protein adsorption. Our findings suggest that selective adsorption control of protein can be achieved by ion irradiation to PVDF surface.