Xiuli Dong

Inactivation of Bacillus anthracis spores by single-walled carbon nanotubes coupled with oxidizing antimicrobial chemicals.

In this study, we investigated the sporicidal effects of single-walled carbon nanotubes (SWCNTs) and SWCNTs combined with oxidizing antimicrobial chemicals, H₂O₂ and NaOCl, on B. anthracis spores. The results indicated that treatment with SWCNTs alone exhibited little sporicidal effect on B. anthracis spores, while treatment with H₂O₂ or NaOCl alone showed moderate sporicidal effect. The combination treatment with SWCNTs (100 μg/mL) and H₂O₂ (1.5%) or NaOCl (0.25%) exhibited much stronger sporicidal effect on the spores, compared to treatment with H₂O₂ or NaOCl alone at the same concentrations, doubling the log reduction of viable spore number (∼3.3 log vs ∼1.6 log). Such enhanced sporicidal efficiency was due to the synergistic effect contributed by the two individual antimicrobial mechanisms of SWCNTs and the oxidizing antimicrobial chemicals. The ordered sequential treatment with SWCNTs and H₂O₂ or NaOCl revealed that SWCNTs played the key role in making the spores more permeable/susceptible to chemicals. This study demonstrated the potential of combination treatment with SWCNTs and oxidizing antimicrobial agents in developing highly effective sporicidal agents/methods.

Inhibitory effects of nisin-coated multi-walled carbon nanotube sheet on biofilm formation from Bacillus anthracis spores.

Multi-walled carbon nanotube (MWCNT) sheet was fabricated from a drawable MWCNT forest and then deposited on poly(methyl methacrylate) film. The film was further coated with a natural antimicrobial peptide nisin. We studied the effects of nisin coating on the attachment of Bacillus anthracis spores, the germination of attached spores, and the subsequent biofilm formation from attached spores. It was found that the strong adsorptivity and the super hydrophobicity of MWCNTs provided an ideal platform for nisin coating. Nisin coating on MWCNT sheets decreased surface hydrophobicity, reduced spore attachment, and reduced the germination of attached spores by 3.5 fold, and further inhibited the subsequent biofilm formation by 94.6% compared to that on uncoated MWCNT sheet. Nisin also changed the morphology of vegetative cells in the formed biofilm. The results of this study demonstrated that the anti-adhesion and antimicrobial effect of nisin in combination with the physical properties of carbon nanotubes had the potential in producing effective anti-biofilm formation surfaces.

Superior Antibacterial Activity of Photochemical Synthesized Ag-CNTComposites and their Synergistic Effects in Combination with otherAntimicrobial Agents

Silver nanoparticle-modified multiwalled carbon nanotubes (MWCNTs) nanocomposites (AgCNTs) were synthesized by photochemical reduction method, their antimicrobial effect on both Gram negative and Gram positive bacteria, using E. coli and Bacillus anthracis as model bacteria, respectively, were investigated. The results indicated that AgCNTs exhibited more potent antibacterial effects against both Gram negative and Gram positive bacterium compared to Ag nanoparticles (Ag NPs). The minimal inhibitory concentrations (MICs) of AgCNTs against E. coli cells (0.5 μg/mL) and B. anthracis cells (0.8 μg/mL) was 1/20 times and 1/17.5 of the MICs of Ag NPs against E. coli and B. anthracis, respectively. Further study on the antibacterial effect of combination treatment of AgCNTs with oxidizing antimicrobial agents (NaOCl or H2O2) to E. coli cells indicated a partial synergistic or a synergistic effect using the fractional inhibitory concentration (FIC) index test or isololograms. The combination treatment of AgCNTs with a natural peptide, nisin, also exhibited enhanced inhibitory effect on E. coli growth, as significant delays in growth of E. coli cells treated by the combination of 0.2 μg/mL AgCNTs and 4 or 8 μg/mL nisin was observed compared to AgCNTs alone nisin alone treatment. The synergistic or enhanced effect of the combination of AgCNTs with other antimicrobial relied on the combination of different action mechanisms in which AgCNTs played a role to damage cell membrane which allowed easier access for other small antimicrobial molecules to penetrate into cells. Such combination strategy could be broadly applicable to the improvement of existing antimicrobial methods or design/discover new effective antimicrobial agents/methods.

Carbon Dots’ Antiviral Functions Against Noroviruses

This study reported the first assessment of carbon dots’ (CDots) antiviral activity to human norovirus virus-like-particles (VLPs), GI.1 and GII.4 VLPs. CDots with different surface passivation molecules, 2,2′-(ethylenedioxy)bis(ethylamine) (EDA)-CDots and 3-ethoxypropylamine (EPA)-CDots, were synthesized and evaluated. The results indicated both EDA- and EPA- CDots were highly effective to inhibit both strains of VLPs’ bindings to histo-blood group antigens (HBGA) receptors on human cells at CDots concentration of 5 µg/mL, with EDA-CDots achieving 100% inhibition and EPA CDots achieving 85–99% inhibition. At low CDots concentration (2 µg/mL), positively charged EDA-CDots exhibited higher inhibitory effect (~82%) than non-charged EPA-CDots (~60%), suggesting the surface charge status of CDots played a role in the interactions between CDots and the negatively charged VLPs. Both types of CDots also exhibited inhibitory effect on VLP’s binding to their respective antibodies, but much less effective than those to HBGA binding. After CDots treatments, VLPs remained intact, and no degradation was observed on VLPs’ capsid proteins. Taken together, the observed antiviral effects of CDots on noroviruses were mainly through the effective inhibition of VLPs’ binding to HBGA receptors and moderate inhibition of VLPs’ binding to their antibodies, without affecting the integrity of viral capsid protein and the viral particle.

Antibacterial effects of carbon dots in combination with other antimicrobial reagents

This study was designed to investigate the antimicrobial effects of CDots in combination with other antimicrobial reagents, including H2O2, Na2CO3, and AcOH (acetic acid). CDots were synthesized and passivated with 2,2’-(ethylenedioxy)bis(ethylamine) (EDA). The minimal inhibitory concentration (MIC) of CDots was 64 μg/mL on both Gram negative bacteria E.coli cells and Gram positive bacteria Bacillus subtilis cells. When CDots were combined with H2O2, antibacterial synergistic effects were observed based on the fractional inhibitory concentration (FIC) index, and further confirmed by an isobologram analysis and viable cell number counting methods. With the combination treatment of 10 μg/mL CDots with 8.82 mM H2O2, the viable E.coli cell numbers decreased 2.46 log, which was significant lower than the log reduction from 8.82 mM H2O2 (1.57 log) or 10 μg/mL CDots (0.14 log) treatment alone. However, the combination of CDots with Na2CO3 or AcOH did not show synergistic effects, instead, exhibiting indifference effects according to the FIC index. This study indicated that the combination of CDots with their synergistic antimicrobial reagents, such as H2O2, could reach the goal of inhibiting bacteria growth by using lower concentration of each individual chemical in the combination than using one chemical treatment alone, reduce the risks imposed on environmental health and the possibilities of the development of microbial resistances.

ANTIMICROBIAL EFFECTS OF CARBON NANOTUBES

Inactivation of pathogens from environment and inhibition of biofilm formation on various surfaces are important for biosafety, biosecurity and public health. Carbon nanotubes (CNTs) possess antimicrobial effects in addition to their unique optical, electrical, mechanical and thermal properties. This review summarizes the antimicrobial effects of single walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) in suspensions and on CNT contained surfaces. To increase antimicrobial effects, CNT composites containing other antimicrobial reagents are introduced. Also described are the possible antimicrobial mechanisms of CNTs.

Carbon dot incorporated multi-walled carbon nanotube coated filters for bacterial removal and inactivation

Multi-walled carbon nanotube (MWCNT) filters incorporated with carbon quantum dots (CDots) or single-walled carbon nanotubes (SWCNTs) were produced for bacteria removal from aqueous solutions and also for inactivating the captured bacteria. TMTP Millipore membranes were used as the base of these filters. The results showed that filters with higher MWCNT loading had higher bacterial removal efficiencies. Filters with a MWCNT loading of 4.5 mg were highly effective at removing bacteria from aqueous solution, resulting in a log reduction of 6.41, 6.41, and 5.41 of E. coli cell numbers in filtrates compared to MWCNT filters without coating, MWCNTs filters with 0.15mg CDot coating, and MWCNTs filters with 0.15mg SWCNT coating, respectively. Ionic strength played an important role in bacteria removal. A higher NaCl concentration resulted in higher bacteria removal efficiencies of the filters. Both CDot coatings and SWCNT coatings did not significantly affect the MWCNT filter effects (P > 0.05). The coatings, especially CDot coatings, significantly inhibited the activities of bacteria retained on the filter surfaces (P < 0.05). The inhibitory rates were 94.21% or 73.17% on the MWCNT filter surfaces coated with 0.2 mg CDots or SWCNTs, respectively. These results demonstrated that MWCNT filters with CDot coatings were highly effective to remove bacteria from water and to inhibit the activities of the captured bacteria on filter surfaces.

Evaluation of Bio-Layer Interferometric Biosensors for Label-Free Rapid Detection of Norovirus Using Virus Like Particles

This study evaluated the label-free bio-layer interferometric (BLI) biosensor for the detection of norovirus (NoV) using two types of virus like particles (VLPs) that represent human NoV GI.1 and GII.4. To construct biosensors for NoV GI.1 and GII.4 detection, the commercial AMC sensors, on which anti-mouse Fc-specific antibodies were preimmobilized on the surfaces, were further bound with the capture antibodies mAb3901 and mAb NS14, respectively, by using the Blitz system. The kinetics of immobilization of capture antibodies on the AMC sensors demonstrated that mAb3901 and mAb NS14 reached saturated binding phase almost at the same time (~415 s). The optimal concentration of capture antibodies for immobilization was 15 μg/mL for both mAb3901 and mAb NS14. The AMC sensors loaded more mAb NS14 than mAb3901 at the same binding condition. The biosensors constructed by immobilization of the capture antibodies at their optimal concentration showed tight binding interactions with their respective GI.1 VLPs and GII.4 VLPs, with the affinity constant of 6.01 × 10-7 M and 2.01 × 10-7 M, respectively. For both biosensors, the VLPs binding rates were linearly increased with the increase of VLP concentrations. These biosensors were able to detect GI.1 or GII.4 VLPs at the concentration of 5 μg/mL in PBS, and showed intense and stable binding interactions at VLP concentration of 10 μg/mL and above. The mAb NS14-immoblized biosensors for GII.4 VLP detection were more sensitive than the mAb3901-immoblized biosensors for GI.1 VLP detection. This detection technique was label-free, easy, rapid (2 min), and accurate, requiring a very small sample volume (4 μL).