Daylight-driven rechargeable antibacterial and antiviral nanofibrous membranes for bioprotective applications

Si, Yang; Zhang, Zheng; Wu, Wanrong; Fu, Qiuxia; Huang, Kang; Nitin, Nitin; Ding, Bin; Sun, Gang

To gain insight into the bactericidal mechanism of the RNMs, we investigated the morphological changes of bacteria after contacts with the RNMs. As shown in Fig. 4 (E to H) , both E. coli and L. innocua cells contacting with the control samples remained smooth and in their respective rodlike morphologies with intact cell membranes. In sharp contrast, cellular deformation and surface collapse were found on the bacterial cells after exposure to the BDCA-RNM after 1 hour of light exposure. Most of the cells were lysed, and numerous small portions of debris were observed. This observation was also supported by the live/dead bacterial fluorescence staining assays. The bacteria in contact with the control and BDCA-RNM were washed out and first stained with a cell-nonpermeant propidium iodide (PI) red dye, which is only able to penetrate cells with compromised membranes, and then, they were counterstained with a cell-permeant SYBR Green (SG) dye, which can stain the nucleic acids of both intact and permeabilized cells. As shown in Fig. 4 (I to L), numerous live E. coli and L. innocua were observed in green color after contacting the control samples, whereas little red color was found. In contrast, upon 1-hour contact with the BDCA-RNM under light conditions, the observed green fluorescence signals were significantly decreased, and all cells in green color were almost exclusively in red color as well, revealing that most of bacterial cells were disrupted or lysed without any integrated morphology. To further assess the damage induced on bacterial cell membranes, we detected leakage of nucleic acids and proteins from the bacterial cells after contacting with BDCA-RNM samples. Supernatants of pelleted culture were analyzed for spectrophotometric absorbance readings at 260 and 280 nm, which corresponded to the characteristic peaks of nucleic acids and proteins, respectively. As shown in Fig. 4 (M and N) , nearly no organic matter was detected from the supernatant after contacting with the control samples. Meanwhile, significant leakage of nucleic acids and proteins was observed for the E. coli and L. innocua after contacting with BDCA-RNM, either under light exposure or under dark conditions, confirming the disruption of the bacterial cell walls and membranes. These results suggested that the bactericidal function of the BDCA-RNMs should be similar to that of peroxide disinfectants commonly used in medical sterilization, which involve bacterial cell wall and membrane disruption (33, 48) . Moreover, contact killing and free ROS release are both possible mechanisms, but the contact killing plays a dominant role for the RNMs. Because the ROS radicals have a quite short lifetime of <10 ms with negligible migration distance, the stable H 2 O 2 was not able to reach the critical biological activity level in such a short time (<10 min) (30, 33) . Therefore, the use of the RNMs is advantageous to avoid the undesirable free ROS release and accumulation by using ROS smartly, effectively, and safely. Antiviral function, killing or inactivating viruses, is another essential requirement for bioprotective PPE materials, especially for the increasingly viral outbreaks that the public is facing today. To evaluate the antiviral performance of the RNMs, we tested the membrane surface with T7 bacteriophage and evaluated the viral activity by E. coli-based stationary phase plating assay. T7 phage is a nonenveloped double-stranded DNA virus and has a single proteinace