Ultrasonic-assisted synthesis of lignin-capped Cu₂O nanocomposite with antibiofilm properties

Under ultrasonication, cuprous oxide (Cu₂O) microparticles (<5 µm) were fragmented into nanoparticles (NPs, ranging from 10 to 30 nm in diameter), and interacted strongly with alkali lignin (Mw = 10 kDa) to form a nanocomposite. The ultrasonic wave generates strong binding interaction between lignin and Cu₂O. The L-Cu nanocomposite exhibited synergistic effects with enhanced antibiofilm activities against E. coli, multidrug-resistant (MDR) E. coli, S. aureus (SA), methicillin-resistant SA, and P. aeruginosa (PA). The lignin-Cu₂O (L-Cu) nanocomposite also imparted notable eradication of such bacterial biofilms. Experimental evidence unraveled the destruction of bacterial cell walls by L-Cu, which interacted strongly with the bacterial membrane. After exposure to L-Cu, the bacterial cells lost the integrated structural morphology. The estimated MIC for biofilm inhibition for the five tested pathogens was 1 mg/mL L-Cu (92 % lignin and 8 % Cu₂ONPs, w/w %). The MIC for bacterial eradication was noticeably lower; 0.3 mg/mL (87 % lignin + 13 % Cu₂ONPs, w/w %) for PA and SA, whereas this value was appreciably higher for MDR E. coli (0.56 mg/mL, 86 % lignin and 14 % Cu₂O NPs). Such results highlighted the potential of L-Cu as an alternative to neutralize MDR pathogens.