A two-step bioluminescence assay for optimizing antibacterial coating of hollow-fiber membranes with polydopamine in an integrative approach

Pure-water filtration membranes are often fouled by bacterial biofilms. Antibacterial coatings for preventing biofilm formation on such membranes should not rely on leaching of inhibiting compounds but should only be effective on surface contact. Certified assays for antibacterial coatings do not sufficiently exclude leaching effects and involve nutrient-rich cultivation media that do not correspond to conditions in pure-water systems. In this study, a two-step bioluminescence assay was developed for optimizing an antibacterial coating of PES/PVP ultrafiltration hollow-fiber membranes with a polydopamine as a sustainable, bio-inspired material for preventing bacterial biofilm formation. In the first step, leaching of the antimicrobial coating was analyzed by a bioluminescence assay with supernatants generated by washing coated membranes. In the second step, bioluminescence of bacterial biofilms on coated and uncoated membranes was measured using a nutrient-poor medium resembling site-specific conditions. Based on this bioluminescence assay, an optimized protocol for the coating process could be established by acidic polymerization of dopamine using 2 g/L sodium periodate and 4 g/L dopamine at 40 °C for 20 min reaction time. With coatings produced in this way, bioluminescence was reduced on coated membranes only while the corresponding supernatants exhibited no inhibitory effects.