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Abstract Carbon dots represent a rapidly advancing and expanding research field, with a large number of literature reports on their potential technological applications including those relevant to food safety. In this article, the dot samples prepared by the deliberate chemical functionalization of preexisting small carbon nanoparticles or by thermal carbonization of various organic precursors under different processing conditions are highlighted and critiqued for their similarities and differences in sample structure-morphology and properties, especially antimicrobial properties for their food safety–related uses. Also highlighted and discussed are representative recent examples for the use of dot samples to inactivate foodborne pathogens, disrupt biofilms or prevent their formation, and extend the shelf life of food products, which involve different antibacterial mechanisms. Some perspectives on the further development of the carbon dots–based/derived antimicrobial platform and related excellent application opportunities in food safety are provided. 

Carbon dots (CDots) are classically defined as small carbon nanoparticles with effective surface passivation, which, in the classical synthesis, has been accomplished by surface organic functionalization. CDot-like nanostructures could also be produced by the thermal carbonization processing of selected organic precursors, in which the non-molecular nanocarbons resulting from the carbonization are embedded in the remaining organic species, which may provide the passivation function for the nanocarbons. In this work, a mixture of oligomeric polyethylenimine and citric acid in the solid state was used for efficient thermal carbonization processing with microwave irradiation under various conditions to produce dot samples with different nanocarbon content. The samples were characterized in terms of their structural and morphological features regarding their similarity or equivalency to those of the classical CDots, along with their significant divergences. Also evaluated were their optical spectroscopic properties and their photoinduced antimicrobial activity against selected bacterial species. The advantages and disadvantages of the thermal carbonization processing method and the resulting dot samples with various features and properties mimicking those of classically synthesized CDots are discussed. 

Carbon dots (CDots) are classically synthesized by organic functionalization of pre‐existing small carbon nanoparticles, but most of the dot samples reported in the literature are prepared by thermal carbonization processing of selected organic precursors. Highlighted and discussed in this article are the necessity of using proper thermal processing conditions for the carbonization produced samples to be CDots like, the similarities and differences in sample structure and morphology between the two kinds of dot samples, and their associated property and mechanistic consequences. 

Carbon–semiconductor hybrid quantum dots are classical carbon dots with core carbon nanoparticles doped with a selected nanoscale semiconductor. Specifically, on those with the nanoscale TiO2 doping, denoted as CTiO2-Dots, their synthesis and thorough characterization were reported previously. In this work, the CTiO2-Dots were evaluated for their visible light-activated antibacterial function, with the results showing the effective killing of not only Gram-positive but also the generally more resistant Gram-negative bacteria. The hybrid dots are clearly more potent antibacterial agents than their neat carbon dot counterparts. Mechanistically, the higher antibacterial performance of the CTiO2-Dots is attributed to their superior photoexcited state properties, which are reflected by the observed much brighter fluorescence emissions. Also considered and discussed is the possibility of additional contributions to the antibacterial activities due to the photosensitization of the nanoscale TiO2 by its doped core carbon nanoparticles. 

Carbon dots (CDots) are generally defined as small carbon nanoparticles (CNPs) with effective surface passivation, for which the classical synthesis is the functionalization of pre-existing CNPs with organic molecules. However, “dot” samples produced by “one-pot” thermal carbonization of organic precursors are also popular in the literature. These carbonization-produced samples may contain nano-carbon domains embedded in organic matters from the precursors that survived the thermal processing, which may be considered and denoted as “nano-carbon/organic hybrids”. Recent experimental evidence indicated that the two different kinds of dot samples are largely divergent in their photo-induced antibacterial functions. In this work, three representative carbonization-produced samples from the precursor of citric acid–oligomeric polyethylenimine mixture with processing conditions of 200 °C for 3 h (CS200), 330 °C for 6 h (CS330), and microwave heating (CSMT) were compared with the classically synthesized CDots on their photo-induced antiviral activities. The results suggest major divergences in the activities between the different samples. Interestingly, CSMT also exhibited significant differences between antibacterial and antiviral activities. The mechanistic origins of the divergences were explored, with the results of different antimicrobial activities among the hybrid samples rationalized in terms of the degree of carbonization in the sample production and the different sample structural and morphological characteristics. 

Carbon dots (CDots) are small carbon nanoparticles with effective surface passivation by organic functionalization. In the reported work, the surface functionalization of preexisting small carbon nanoparticles with N-ethylcarbazole (NEC) was achieved by the NEC radical addition. Due to the major difference in microwave absorption between the carbon nanoparticles and organic species such as NEC, the nanoparticles could be selectively heated via microwave irradiation to enable the hydrogen abstraction in NEC to generate NEC radicals, followed by in situ additions of the radicals to the nanoparticles. The resulting NEC-CDots were characterized by microscopy and spectroscopy techniques including quantitative proton and 13C NMR methods. The optical spectroscopic properties of the dot sample were found to be largely the same as those of CDots from other organic functionalization schemes. The high structural stability of NEC-CDots benefiting from the radical addition functionalization is highlighted and discussed. 

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.