Lignin-Encapsulated ZnO Nano-Hybrids Exhibit Enhanced Antibacterial and Photocatalytic Activity via ROS-Mediated Oxidative Stress and Bacterial Membrane Disruption.

The sustainable design of multifunctional nanomaterials capable of addressing both biomedical and environmental challenges remains a key frontier in nanotechnology. In this study, we report the green fabrication and biofunctionalization of zinc oxide nanoparticles (ZnO NPs) using lignin, an abundant and renewable polyphenolic biopolymer, to engineer eco-compatible nanohybrids with enhanced physicochemical stability and biological efficacy. Comprehensive characterization confirmed lignin encapsulation and uniform morphology at the nanoscale. Lignin-ZnO nanohybrids displayed significantly enhanced antibacterial and antibiofilm activities against both Escherichia coli and Staphylococcus epidermidis relative to pristine ZnO NPs, exhibiting significantly lower MICs and MBIC50 values. The mechanistic assays performed showed that the enhanced antimicrobial activity was due to oxidative stress induced by reactive oxygen species (ROS), membrane disruption, and enzyme inactivation, as shown by superoxide dismutase (SOD) activity and analyses of cytoplasmic leakage. The lignin-ZnO nanohybrids also exhibited strong antioxidant and anti-inflammatory properties due to the phenolic functionality of lignin, improving their biocompatibility and therapeutic potential. The photocatalytic characterization indicated that around 80% of methylene blue was degraded in 100 min and followed pseudo-first-order kinetics (k = 0.0215 min-1) consistent with the enhanced redox activity from superior electron-hole separation. Docking studies revealed a unique antiadhesive mechanism wherein lignin binds to the S. epidermidis bacterial adhesin protein known as SdrG to block (prevent) binding to fibrinogen, the first step in biofilm development, and this same lignin compound showed high affinities for multiple targets in E. coli such as the AcrB efflux pump and dihydrofolate reductase. Collectively, these results suggest that lignin-functionalized ZnO nanohybrids represents a next-generation, sustainable nanoplatform that integrates antibacterial, antioxidant, anti-inflammatory, and photocatalytic properties for future applications in advanced biomedical and environmental areas.