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 evaluate the antibacterial activity of the RNMs, we challenged the membrane surface with two typical pathogenic bacteria, Gramnegative Escherichia coli O157:H7 and Gram-positive Listeria innocua. For the contact-killing assay, the control (pristine PVA-co-PE nanofibrous membranes) and BDCA-RNM samples with a size of 2 × 2 cm 2 were loaded with 10 ml of 1 × 10 8 colony-forming units (CFU) of a bacterial suspension (2.5 × 10 5 CFU cm −2 ), and the bacterial proliferation was assessed by agar plate counting. Figure 4A depicts the time-dependent antibacterial effect of the BDCA-RNM under daylight irradiation conditions. It was found that the control samples showed significant bacterial growth during incubation even after 1 hour of irradiation. In contrast, the BDCA-RNM showed effective killing of bacteria, achieving 6 log CFU reduction of E. coli and L. innocua in 60-and 30-min daylight irradiation, respectively, which corresponds to a promising contact-killing efficacy of 99.9999%. In comparison, a contact time of 5 to 10 hours is typical for previous photoactive hydrogels to achieve these bacterial reductions (45, 46) , and other photoactive fibrous materials exhibit only up to 4 log CFU reduction but require a contact time of several hours (28, 47) . Moreover, in marked contrast to the traditional photoantimicrobial materials, the BDCA-RNM can store the biocidal activity and kill bacteria under dark conditions, as shown in Fig. 4B . After 1 hour of daylight exposure, the charged BDCA-RNM exhibited 6 log CFU reduction of both E. coli and L. innocua within 120-min contact under dark conditions, which nearly maintained half of the biocidal efficiency compared with the conditions of under lighting. Considering that the HCWs are easy to experience dim light or dark working conditions, this rechargeable biocidal performance is very promising on PPE from the viewpoint of practical bioprotection, serving the biocidal function "always online." In addition, the rechargeable feature is also responsible for the renewed cyclic performance of the RNMs against microorganisms. As shown in Fig. 4 (C and D) , the five cyclic contact-killing tests revealed that the biocidal efficacy was nearly constant with 6 log CFU reduction of the bacteria, no matter with or without light exposure, highlighting the biocidal character of the BDCA-RNMs.