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Carbon dots (CDots) of small carbon nanoparticles with oligomeric polyethylenimine for surface functionalization, coupled with visible light exposure, were found highly effective in the inactivation of bacterial pathogens. In this study, using a representative strain of a major foodborne pathogen – Listeria monocytogenes , as a target, the effects of the CDots treatment at sublethal concentrations on bacterial functions/behaviors related to the biofilm formation ability/potential, including cell attachment and swimming motility, were assessed. On the consequence at molecular level, the expression levels of the genes that are related to cell attachment/adhesion, motility, flagellar synthesis, quorum sensing, and environmental stress response and virulence were found all being up-regulated. 

The carbon/TiO2 hybrid dots (C/TiO2-Dots) are structurally TiO2 nanoparticles (in the order of 25 nm in diameter from commercially available colloidal TiO2 samples) surface-attached by nanoscale carbon domains with organic moieties, thus equivalent to hybrids of individual TiO2 nanoparticles each decorated with many carbon dots. These hybrid dots with exposure to visible light exhibit potent antibacterial properties, similar to those found in neat carbon dots with the same light activation. The results from the use of established scavengers for reactive oxygen species (ROS) to “quench” the antibacterial activities, an indication for shared mechanistic origins, are also similar. The findings in experiments on probing biological consequences of the antibacterial action suggest that the visible light-activated C/TiO2-Dots cause significant damage to the bacterial cell membrane, resulting in higher permeability, with the associated oxidative stress leading to lipid peroxidation, inhibiting bacterial growth. The induced bacterial cell damage could be observed more directly in the transmission electron microscopy (TEM) imaging. Opportunities for the further development of the hybrid dots platform for a variety of antibacterial applications are discussed. 

Electrospun polyacrylonitrile (PAN) nanofibers integrated with different loadings of the photosensitizer rose bengal (RB) were synthesized for photodynamic inactivation of bacteria. Our results suggest that the ionic strength in the medium does not significantly affect the RB release from the RB-integrated electrospun PAN nanofibers (RBiEPNs), which could release RB effectively in phosphate-buffered saline (PBS), physiological saline (0.85% NaCl), and deionized H 2 O. However, the pH of the medium significantly influenced the release of RB. A larger amount of RB was released in PBS at a higher pH (RB release: pH 9.0 > pH 7.4 > pH 5.0). The RBiEPNs depicted high antimicrobial efficacy against both Gram-negative Escherichia coli ( E. coli ) and Gram-positive Bacillus subtilis ( B. subtilis ) bacteria under white light irradiation. The antimicrobial efficacy was potent and immediate against the bacterial cells, especially B. subtilis . The RBiEPNs containing 0.33 wt% RB demonstrated complete bacterial kills for B. subtilis and E. coli cells with log reductions of 5.76 and 5.94 in 30 s and 40 min, respectively. The generation of intracellular reactive oxygen species (iROS) was examined after white light treatment of the bacterial cells in the presence of the RBiEPNs. A significant correlation was found between the amount of iROS and the antimicrobial efficacy of the RBiEPNs. The high antimicrobial efficacy could be attributed to several factors, such as the encapsulation efficiency, loading capacity, and RB release behavior of the RBiEPNs, the presence of white light, and the generation of iROS. Taken together, the facile incorporation of a photosensitizer into polymeric nanofibers via blend electrospinning offers a feasible strategy for water disinfection. 

Herein, we report an effective strategy to maximize the antimicrobial activity of CuWO 4 /CuS hybrid composites, prepared by simply mixing CuWO 4 and CuS nanopowders with varying weight ratios in phosphate buffered saline solution by ultrasound. The tested bacteria included Gram negative (G − ) pathogenic bacteria Salmonella typhi , Gram positive (G + ) pathogenic bacteria Staphylococcus aureus , and G + bacteria Bacillus subtilis . The as-prepared composites exhibited much enhanced antibacterial efficiency compared with individual CuWO 4 and CuS nanopowders under white light irradiation. The checkerboard array analysis revealed that the combination of 8 μg mL −1 CuWO 4 and 2 μg mL −1 CuS was the most efficient and generated the optimal synergistic effect, showing a complete killing effect on all the tested bacteria from 3 strains with ∼5.8 log cell reduction. The significantly enhanced catalytic efficiency can be ascribed to the formation of a type-II heterojunction between CuWO 4 and CuS, which can effectively improve the charge separation efficiency and increase the light absorption. Moreover, the hybrid composites prepared by ultrasound-assisted physical mixing can effectively increase the interface area, which greatly facilitates the charge mobility and transfer in the interfaces between CuWO 4 and CuS. This study offers new insights into the integration of different semiconductors to optimize their synergistic effect on antimicrobial activities for water disinfection. 

This study aimed to address the significant problems of bacterial biofilms found in medical fields and many industries. It explores the potential of classic photoactive carbon dots (CDots), with 2,2′-(ethylenedioxy)bis (ethylamine) (EDA) for dot surface functionalization (thus, EDA-CDots) for their inhibitory effect on B. subtilis biofilm formation and the inactivation of B. subtilis cells within established biofilm. The EDA-CDots were synthesized by chemical functionalization of selected small carbon nanoparticles with EDA molecules in amidation reactions. The inhibitory efficacy of CDots with visible light against biofilm formation was dependent significantly on the time point when CDots were added; the earlier the CDots were added, the better the inhibitory effect on the biofilm formation. The evaluation of antibacterial action of light-activated EDA-CDots against planktonic B. subtilis cells versus the cells in biofilm indicate that CDots are highly effective for inactivating planktonic cells but barely inactivate cells in established biofilms. However, when coupling with chelating agents (e.g., EDTA) to target the biofilm architecture by breaking or weakening the EPS protection, much enhanced photoinactivation of biofilm-associated cells by CDots was achieved. The study demonstrates the potential of CDots to prevent the initiation of biofilm formation and to inhibit biofilm growth at an early stage. Strategic combination treatment could enhance the effectiveness of photoinactivation by CDots to biofilm-associated cells. 

ABSTRACT Foodborne pathogens have long been recognized as major challenges for the food industry and repeatedly implicated in food product recalls and outbreaks of foodborne diseases. This study demonstrated the application of a recently discovered class of visible-light-activated carbon-based nanoparticles, namely, carbon dots (CDots), for photodynamic inactivation of foodborne pathogens. The results demonstrated that CDots were highly effective in the photoinactivation of Listeria monocytogenes in suspensions and on stainless steel surfaces. However, it was much less effective for Salmonella cells, but treatments with higher CDot concentrations and longer times were still able to inactivate Salmonella cells. The mechanistic implications of the observed different antibacterial effects on the two types of cells were assessed, and the associated generation of intracellular reactive oxygen species (ROS), the resulting lipid peroxidation, and the leakage of nucleic acid and proteins from the treated cells were analyzed, with the results collectively suggesting CDots as a class of promising photodynamic inactivation agents for foodborne pathogens. IMPORTANCE Foodborne infectious diseases have long been recognized as major challenges in public health. Contaminations of food processing facilities and equipment with foodborne pathogens occur often. There is a critical need for new tools/approaches to control the pathogens and prevent such contaminations in food processing facilities and other settings. This study reports a newly established antimicrobial nanomaterials platform, CDots coupled with visible/natural light, for effective and efficient inactivation of representative foodborne bacterial pathogens. The study will contribute to promoting the practical application of CDots as a new class of promising nanomaterial-based photodynamic inactivation agents for foodborne pathogens. 

The antiviral function of carbon dots (CDots) with visible light exposure was evaluated, for which the model bacteriophages MS2 as a surrogate of small RNA viruses were used. The results show clearly that the visible light-activated CDots are highly effective in diminishing the infectivity of MS2 in both low and high titer samples to the host E. coli cells, and the antiviral effects are dot concentration- and treatment time-dependent. The action of CDots apparently causes no significant damage to the structural integrity and morphology of the MS2 phage or the breakdown of the capsid proteins, but does result in the protein carbonylation (a commonly used indicator for protein oxidation) and the degradation of viral genomic RNA. Mechanistically the results may be understood in the framework of photodynamic effects that are associated with the unique excited state properties and processes of CDots. Opportunities for potentially broad applications of CDots coupled with visible/natural light in the prevention and control of viral transmission and spread are highlighted and discussed. 

For addressing the ever increasing challenge of multidrug-resistant (MDR) bacterial infections, specifically designed and prepared carbon dots (CDots) of small carbon nanoparticles with surface functionalization–passivation by oligomeric polyethylenimine were found to be readily activated by visible light to effectively and efficiently inactivate MDR bacterial strains. The inactivation was evaluated under various combinations of experimental conditions (dot concentrations, light intensities, and treatment times), with the results collectively suggesting CDots as a new class of promising agents for combating MDR bacteria. Mechanistic origins and implications of the observed strong antibacterial actions as relevant to the photoexcited state processes in CDots and the photodynamically induced cellular damages leading to the death of the bacterial cells were explored, with the results discussed.