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Carbon dots (CDots) have emerged to represent a highly promising new platform for visible/natural light-activated microbicidal agents. In this article, the syntheses, structures, and properties of CDots are highlighted, representative studies on their activities against bacteria, fungi, and viruses reviewed, and the related mechanistic insights discussed. Also highlighted and discussed are the excellent opportunities for potentially extremely broad applications of this new platform, including theranostics uses., Competing Interests: Competing Interests: The authors have declared that no competing interest exists., (© The author(s).)

Background: Carbon quantum dots (CDots) have recently been reported as a new class of visible light activated antimicrobial nanomaterials. This study reports the synergistic photoactivated antimicrobial interactions of CDots with photosensitizers on bacterial cells., Methods: The antimicrobial effects of the CDots with surface passivation molecules 2,2'-(ethylenedioxy)bis(ethylamine) in combination with photosensitizer methylene blue (MB) or toluidine blue (TB) at various concentrations were evaluated against Escherichia coli cells with and without 1-hour visible light illumination. The broth microdilution checkerboard method and isobologram analysis were used for determining if synergistic effect existed between CDots and MB or TB., Results: The results showed that CDots alone at a concentration of 5 μg/mL did not display antimicrobial effects, 1 μg/mL MB alone only decreased 1.86 log of viable cell numbers, but the combination treatment with 5 μg/mL CDots combined with 1 μg/mL MB completely inhibited bacteria growth, resulted in 6.2 log viable cell number reduction, suggesting synergistic interaction between the two. The antimicrobial effects of CDots/TB combination exhibited similarly synergistic effects on E. coli cells. These synergistic effects between CDots and MB or TB were further confirmed using the checkerboard microdilution methods, where the fractional inhibitory concentration index value (0.5) and the isobologram analyses. The synergistic interactions were also correlated to the increased generation of intracellular reactive oxygen species in E. coli cells upon the combination treatments of CDots/MB or CDots/TB., Conclusion: The study demonstrated the synergistic photoactivated antimicrobial effects of CDots in combination with other photosensitizers. Such synergistic effect may open new strategies for developing highly effective antimicrobial methods., Competing Interests: Disclosure The authors report no conflicts of interest in this work.

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.

In this study, the effect of single-walled carbon nanotubes (SWCNTs) on B. anthracis cell growth, spore formation, and spore germination was studied. We found that SWCNTs at a concentration of 100 microg/ml exhibited obvious antimicrobial activity on 10(6) cfu/ml B. anthracis cells. At 300 microg/ml, 1 h of SWCNTs treatment could inactivate B. anthracis cells by approximately 2 log viable cell reduction. The SWCNT treatment did not induce spore formation. We also found that SWCNTs were not effective in the inactivation of B. anthracis spores at concentrations from 50 microg/ml up to 300 microg/ml. Fluorescence microscopy and scanning electron microscopy were used to examine the interactions between SWCNTs and B. anthracis cells/spores. Analysis of these microscopic images suggested that the direct contact between SWCNTs and B. anthracis cells lead to cell membrane damage and the inactivation of cells, whereas the lack of tight direct contact between SWCNTs and spores was the reason accounting for its ineffectiveness in inactivating spores.

This study investigated the effect of SWCNTs' length on their antimicrobial activity to bacterial cells in suspensions. Three different lengths of SWCNTs (<1 μm, 1-5 μm, and ∼5 μm) were tested. At same weight concentration, longer SWCNTs exhibited stronger antimicrobial activity. The fluorescence and SEM images revealed that the longer SWCNTs aggregated with bacterial cells more effectively, whereas short length SWCNTs tended to aggregate themselves without involving many bacterial cells. Moreover, longer SWCNTs exhibited more pronounced concentration-dependence and treatment time-dependence on their antimicrobial activity.

In the study, we explored the antimicrobial activities of single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs) with different surface groups to bacterial pathogens, including Gram-negative vs Gram-positive species and rod-shaped vs round-shaped species. We report here for the first time that SWNTs' antimicrobial activity is buffer and concentration dependent, and the charge effect of functional groups on the surface of carbon nanotubes (CNTs) is not a critical factor. SWNTs with surface groups of -OH and -COOH exhibited extremely strong antimicrobial activity to both Gram-positive and Gram-negative bacterial cells in DI water and 0.9% NaCl solution regardless of cell shape, but they did not exhibit antimicrobial activity in PBS buffer and brain heart infusion broth. The antimicrobial activities of these two SWNTs increased with their concentration and treatment time. In DI water or 0.9% NaCl solution, SWNTs-OH and SWNTs-COOH started to show their antimicrobial activity at approximately 50 microg/mL; when their concentration increased to 200-250 microg/mL, they could inactivate 10(7) cfu/mL Salmonella cells in 15 min. The approximately 7 log reduction in viable cell count achieved by this CNTs-based method exceeded those of many reported antimicrobial methods. SWNTs-NH2 only exhibited antimicrobial activity at higher concentrations. MWNTs with surface groups of -OH, -COOH, and -NH2 did not show any significant antimicrobial activity to all tested bacterial cells in any of the tested buffers at concentrations up to 500-875 microg/mL. Formation of cell-CNTs aggregates were studied using fluorescence and electron scanning microscopes. The possible mechanism of SWNTs' antimicrobial activities was also discussed.

Carbon dots (CDots) are generally defined as small-carbon nanoparticles with surface organic functionalization and their classical synthesis is literally the functionalization of preexisting carbon nanoparticles. Other than these "classically defined CDots", however, the majority of the dot samples reported in the literature were prepared by thermal carbonization of organic precursors in mostly "one-pot" processing. In this work, thermal processing of the selected precursors intended for carbonization was performed with conditions of 200 °C for 3 h, 330 °C for 6 h, and heating by microwave irradiation, yielding samples denoted as CS200, CS330, and CSMT, respectively. These samples are structurally different from the classical CDots and should be considered as "nano-carbon/organic hybrids". Their optical spectroscopic properties were found comparable to those of the classical CDots, but very different in the related photoinduced antibacterial activities. Mechanistic origins of the divergence were explored, with the results suggesting major factors associated with the structural and morphological characteristics of the hybrids. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]