XPS characterization of the surface immobilization of antibacterial furanones

Brominated furanones have attracted recent interest as antibacterial compounds. To utilize them as protective coatings in biomedical device applications, they must be covalently immobilized onto solid surfaces; however, interfacial coupling protocols developed for other biomolecules are not applicable to furanones. An azide reaction scheme has enabled covalent immobilization onto fluorinated ethylene propylene copolymer but its chemistry is less predictable, requiring detailed characterization by XPS and tapping mode AFM after each step of the immobilization sequence. XPS curve fitting resolved components in the C 1s, N 1s and Br 3d regions. Angle dependent XPS was used to assess the depth distributions and layer thicknesses. The results indicated successful covalent immobilization of furanones; however, side reactions occurred. In addition to the expected CBr, a contribution from bromine ion (Br⁻) was detected, indicating that photo-degradation of furanones took place during UV illumination, and this reaction was found to increase with illumination time. The Br⁻ was removed by washing with water, whereas the CBr signal from immobilized furanone remained. Spectroscopic characterization will assist in elucidating the structure of furanone coatings, understanding their mode of action when covalently immobilized on surfaces, and rationally designing and optimizing an effective antibacterial coating for biomedical applications.