No abstract

Cellulose nanocrystals (CNCs) have emerged as a sustainable nanomaterial for several environmental applications, including the development of novel antimicrobial agents. Although previous studies have reported antibacterial activity for CNCs, their toxicity mechanism to bacterial cells is still unknown. Here, we investigate the toxicity of CNCs dispersed in water and coated surfaces against Escherichia coli cells. CNC-coated surfaces were able to inactivate approximately 90% of the attached E. coli cells, confirming potential of CNCs to be applied as a sustainable and cost-effective antibiofouling nanomaterial. The toxicity of CNCs in a suspension was concentration-dependent, and an inhibitory concentration (IC50%) of 200 μg/mL was found. Glutathione and 2′,7′-dichlorodihydrofluorescein diacetate (H2DCFA) assays were conducted to evaluate the role of oxidative stress in the CNC toxicity mechanism. Our findings showed that oxidative stress has no significant effect on the antimicrobial activity of CNC. In contrast, scanning electron microscopy (SEM) images and a leakage assay performed with dye-encapsulated phospholipid vesicles indicated that CNCs inactivate bacteria by physically damaging their cell membrane. CNC interaction with dye-encapsulated vesicles resulted in a dye leakage corresponding to 43% of the maximum value, thus confirming that contact-mediated membrane stress is the mechanism governing the toxicity of CNCs to bacteria cells.

In this study, we were able to impart antimicrobial properties onto the surface of a commercial thin-film composite (TFC) membrane using sustainably derived cellulose nanocrystals (CNC) extracted from elephant grass (Pennisetum purpureum) leaves. Carboxylic acid-containing CNC were chemically bound to the amine-terminated polyamide active layer of TFC membranes using a cross-linking reaction. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectroscopy were conducted to confirm the presence of CNC on the membrane surface. TFC membranes functionalized with needle-like and antimicrobial CNC nanoparticles showed robust toxicity to bacteria, inactivating ∼89% of attached Escherichia coli cells under contact. These findings establish that functionalization with CNC is a promising approach for mitigating biofouling on TFC membranes and substantiates the application of sustainable materials for the design of the next-generation membranes for water purification.