"Attacking-Attacking" Anti-biofouling Strategy Enabled by Cellulose Nanocrystals-Silver Materials.

The development of high-performance anti-biofouling surfaces is paramount for controlling bacterial attachment and biofilm growth in biomedical devices, food packing, and filtration membranes. Cellulose nanocrystals (CNCs), a carbon-nanotube-like nanomaterial, have emerged as renewable and sustainable antimicrobial agents. However, CNCs inactivate bacteria under contact-mediated mechanisms, limiting its antimicrobial property mostly to the attached bacteria. This study describes the combination of CNCs with silver nanoparticles (CNC/Ag) as a strategy to increase their toxicity and anti-biofouling performance. CNC/Ag-coated surfaces inactivated over 99% of the attached Escherichia coli and Bacillus subtilis cells compared to 66.9 and 32.9% reduction shown by the pristine CNC, respectively. CNC/Ag was also very toxic to planktonic cells, displaying minimal inhibitory of 25 and 100 μg/mL against B. subtilis and E. coli, respectively. CNC/Ag seems to inactivate bacteria through an "attacking-attacking" mechanism where CNCs and silver nanoparticles play different roles. CNCs can kill bacteria by piercing the cell membrane. This physical membrane stress-mediated mechanism is demonstrated as lipid vesicles release their encapsulated dye upon contact with CNCs. Once the cell membrane is punctured, silver ions can enter the cell passively and compromise the integrity of DNA and other organelles. Inside the cells, Ag+ may damage the cell membrane by selectively interacting with sulfur and nitrogen groups of enzymes and proteins or by harming DNA via accumulation of reactive oxygen species. Therefore, CNC/Ag toxicity seems to combine the puncturing effect of the needle-like CNC and the silver's ability to impair the cell membrane and DNA functionalities.