Extracellular bacterial inactivation proceeding without Cu-ion release: Drastic effects of the applied plasma energy on the performance of the Cu-polyester (PES) samples

The widely different effects of Cu-polyester (PES) sputtered by high power impulse magnetron sputtering (HIPIMS) compared to the lower energy direct current magnetron sputtering (DCMS) leading to bacterial inactivation are addressed during the course of this study. The amounts of Ar+ and Cu/Cu-2-ions generated by HIPIMS (20 A) in the plasma was about five times the amounts detected when using for DCMS (0.3 A), but the relative distribution of these three ionic-species was similar. HIPIMS sputtered Cu-polyester (Cu-PES) at 20 A did not release Cu-ions after a few bacterial inactivation cycles but still lead to complete E. coil inactivation. Unambiguous separation of the intracellular Cu-ions effects and of the extracellular surface-contact was possible comparing the inactivation of wild E. coli to the inactivation of genetically modified porinless E. coll. The optical properties and sample microstructure of the Cu-PES samples were determined by diffuse reflectance spectroscopy (DRS) and by scanning transmission electron microscopy (STEM-HAADF). High-density films were obtained by HIPIMS in contrast to the low-density films prepared by DCMS. The DCMS sputtered Cu-PES presented large amounts of O-interstitial voids. A redox mechanism in bacterial inactivation was detected by X-ray photoelectron spectroscopy (XPS) by monitoring the Cu(I)Cu(II) species within the bacterial inactivation time.