Rapid radiation degradation in the XPS analysis of antibacterial coatings of brominated furanones

Brominated furanones are promising antibacterial compounds, both in solution and immobilized on solid surfaces, and there is interest in their utilization as protective coatings on biomedical devices to combat device-centered infections. The rational design and optimization of antibacterial furanone coatings requires detailed spectroscopic surface characterization of the coatings produced and correlation of surface analysis data with antibacterial performance. However, as reported in this study, the extreme sensitivity of brominated furanones to radiation damage in the course of XPS analysis greatly complicates characterization. Our data show that rapid degradation occurs, as shown by the emergence of a signal assignable to Br- ion in the Br 3d spectrum. This Br- is water soluble as shown by washing experiments, whereas the C-Br signal does not become reduced during washing, consistent with covalent interfacial immobilization of the furanone molecules. Furanone molecules were immobilized onto two different hydrogel interlayers (polyacrylic acid and polyethylene oxide (PEO)), and XPS analyses show that the interlayers did not suffer significant radiation degradation; the damage is limited to the furanone molecules. The results of this study may assist in XPS analyses of other brominated compounds on surfaces; the possibility of Br- ions deriving from XPS analysis-damage must be investigated before assigning their generation to side reactions in the coating or surface-modification procedure. Copyright (C) 2006 John Wiley & Sons, Ltd.