Airborne transmission of SARS-CoV-2 plays a critical role in spreading COVID-19. To
protect public health, we designed and fabricated electrospun nanofibrous air filters
that hold promise for applications in personal protective equipment (PPE) and the indoor
environment. Due to ultrafine nanofibers (∼300 nm), the electrospun air filters
had a much smaller pore size in comparison to the surgical mask and cloth masks (a
couple of micrometers versus tens to hundreds of micrometers). A coronavirus strain
served as a SARS-CoV-2 surrogate and was used to generate aerosols for filtration
efficiency tests, which can better represent SARS-CoV-2 in comparison to other agents
used for aerosol generation in previous studies. The electrospun air filters showed
excellent performance by capturing up to 99.9% of coronavirus aerosols, which
outperformed many commercial face masks. In addition, we observed that the same
electrospun air filter or face mask removed NaCl aerosols equivalently or less
effectively in comparison to the coronavirus aerosols when both aerosols were generated
from the same system. Our work paves a new avenue for advancing air filtration by
developing electrospun nanofibrous air filters for controlling SARS-CoV-2 airborne
transmission.
Understanding the transformation
of graphitic carbon nitride (g-C3N4) is essential
to assess nanomaterial robustness
and environmental risks. Using an integrated experimental and simulation
approach, our work has demonstrated that the photoinduced hole (h+) on g-C3N4 nanosheets significantly
enhances nanomaterial decomposition under •OH attack.
Two g-C3N4 nanosheet samples D and M2 were synthesized,
among which M2 had more pores, defects, and edges, and they were subjected
to treatments with •OH alone and both •OH and h+. Both D and M2 were oxidized and released nitrate
and soluble organic fragments, and M2 was more susceptible to oxidation.
Particularly, h+ increased the nitrate release rate by
3.37–6.33 times even though the steady-state concentration
of •OH was similar. Molecular simulations highlighted
that •OH only attacked a limited number of edge-site
heptazines on g-C3N4 nanosheets and resulted
in peripheral etching and slow degradation, whereas h+ decreased
the activation energy barrier of C–N bond breaking between
heptazines, shifted the degradation pathway to bulk fragmentation,
and thus led to much faster degradation. This discovery not only sheds
light on the unique environmental transformation of emerging photoreactive
nanomaterials but also provides guidelines for designing robust nanomaterials
for engineering applications.
Biofilms are a cluster of bacteria embedded in extracellular polymeric substances (EPS) that contain a complex composition of polysaccharides, proteins, and extracellular DNA (eDNA). Desirable mechanical properties of the biofilms are critical for their survival, propagation, and dispersal, and the response of mechanical properties to different treatment conditions also sheds light on biofilm control and eradication in vivo and on engineering surfaces. However, it is challenging yet important to interrogate mechanical behaviors of biofilms with a high spatial resolution because biofilms are very heterogeneous. Moreover, biofilms are viscoelastic, and their time-dependent mechanical behavior is difficult to capture. Herein, we developed a powerful technique that combines the high spatial resolution of the atomic force microscope (AFM) with a rigorous history-dependent viscoelastic analysis to deliver highly spatial-localized biofilm properties within a wide time-frequency window. By exploiting the use of static force spectroscopy in combination with an appropriate viscoelastic framework, we highlight the intensive amount of time-dependent information experimentally available that has been largely overlooked. It is shown that this technique provides a detailed nanorheological signature of the biofilms even at the single-cell level. We share the computational routines that would allow any user to perform the analysis from experimental raw data. The detailed localization of mechanical properties in space and in time-frequency domain provides insights on the understanding of biofilm stability, cohesiveness, dispersal, and control.
Pathogenic biofilms raise significant health and economic concerns, because these bacteria are persistent and can lead to long-term infections in vivo and surface contamination in healthcare and industrial facilities or devices. Compared with conventional antimicrobial strategies, photocatalysis holds promise for biofilm control because of its broad-spectrum effectiveness under ambient conditions, low cost, easy operation, and reduced maintenance. In this study, we investigated the performance and mechanism of Staphylococcus epidermidis biofilm control and eradication on the surface of an innovative photocatalyst, graphitic carbon nitride (g-C 3 N 4 ), under visible-light irradiation, which overcame the need for ultraviolet light for many current photocatalysts (e.g., titanium dioxide (TiO 2 )). Optical coherence tomography and confocal laser scanning microscopy (CLSM) suggested that g-C 3 N 4 coupons inhibited biofilm development and eradicated mature biofilms under the irradiation of white light-emitting diodes. Biofilm inactivation was observed occurring from the surface toward the center of the biofilms, suggesting that the diffusion of reactive species into the biofilms played a key role. By taking advantage of scanning electron microscopy, CLSM, and atomic force microscopy for biofilm morphology, composition, and mechanical property characterization, we demonstrated that photocatalysis destroyed the integrated and cohesive structure of biofilms and facilitated biofilm eradication by removing the extracellular polymeric substances. Moreover, reactive oxygen species generated during g-C 3 N 4 photocatalysis were quantified via reactions with radical probes and 1 O 2 was believed to be responsible for biofilm control and removal. Our work highlights the promise of using g-C 3 N 4 for a broad range of antimicrobial applications, especially for the eradication of persistent biofilms under visible-light irradiation, including photodynamic therapy, environmental remediation, food-industry applications, and self-cleaning surface development.
To address the challenge of the airborne transmission of SARS-CoV-2, photosensitized
electrospun nanofibrous membranes were fabricated to effectively capture and inactivate
coronavirus aerosols. With an ultrafine fiber diameter (∼200 nm) and a small pore
size (∼1.5 μm), optimized membranes caught 99.2% of the aerosols of the
murine hepatitis virus A59 (MHV-A59), a coronavirus surrogate for SARS-CoV-2. In
addition, rose bengal was used as the photosensitizer for membranes because of its
excellent reactivity in generating virucidal singlet oxygen, and the membranes rapidly
inactivated 97.1% of MHV-A59 in virus-laden droplets only after 15 min irradiation of
simulated reading light. Singlet oxygen damaged the virus genome and impaired virus
binding to host cells, which elucidated the mechanism of disinfection at a molecular
level. Membrane robustness was also evaluated, and in general, the performance of virus
filtration and disinfection was maintained in artificial saliva and for long-term use.
Only sunlight exposure photobleached membranes, reduced singlet oxygen production, and
compromised the performance of virus disinfection. In summary, photosensitized
electrospun nanofibrous membranes have been developed to capture and kill airborne
environmental pathogens under ambient conditions, and they hold promise for broad
applications as personal protective equipment and indoor air filters.
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