The urgency underlying the work is difficult to overstate. Multidrug-resistant Gram-negative infections, methicillin-resistant Staphylococcus aureus, and hospital-acquired sepsis continue to claim lives at rates that conventional antibiotics struggle to contain. The World Health Organization has repeatedly flagged antibiotic resistance as one of the defining health crises of the century, and the problem is compounded by biofilms: organized communities of bacteria wrapped in a self-produced extracellular polymeric matrix that shields them from both immune attack and antimicrobial drugs. Biofilms colonize medical devices, implants, wounds, dental surfaces, water systems and food-processing equipment, and bacteria within them can exhibit tolerance levels hundreds to thousands of times higher than their free-floating counterparts. Traditional antibacterial approaches, the review argues, are increasingly outmatched by this dual threat of resistance and biofilm persistence.

Carbon dots offer a chemically distinctive answer. First reported in 2004 and popularized by seminal work on bright, quantum-sized photoluminescent carbon nanoparticles, these materials typically measure less than ten nanometers and consist of a carbonaceous core decorated with surface functional groups such as carboxyl, hydroxyl and amine moieties. Unlike semiconductor quantum dots containing cadmium or lead, carbon dots are generally built from benign, abundant precursors ranging from citric acid and urea to plant extracts, bacteria and food waste, giving them an environmental and biocompatibility profile that is difficult for heavy-metal nanomaterials to match. Their optical properties are equally compelling: strong fluorescence, tunable emission across the visible and near-infrared spectrum, high photostability, and in some cases room-temperature phosphorescence or aggregation-induced emission. The review contrasts these attributes with conventional semiconductor quantum dots and organic fluorescent dyes, finding carbon dots competitive or superior in biocompatibility, cost and functional versatility.

The mechanistic heart of the review dissects how carbon dots actually kill bacteria, grading the strength of evidence for each proposed pathway. The most thoroughly documented mechanism is the generation of reactive oxygen species. When photoexcited, carbon dots can transfer energy or electrons to oxygen molecules, producing singlet oxygen, superoxide, hydroxyl radicals and hydrogen peroxide through both type I and type II photodynamic pathways. These reactive species oxidize bacterial lipids, proteins and DNA, inflicting damage that is difficult for microbes to counter because it strikes multiple targets simultaneously rather than a single enzyme or receptor. Intersystem crossing and heteroatom doping, particularly with nitrogen, phosphorus or sulfur, tune the efficiency of this ROS production, and studies with chemiluminescent carbon nanodots have shown bacteria can be destroyed even by the dots’ own emitted light.

Physical disruption of the bacterial membrane constitutes a second major killing route. Bacterial surfaces carry a net negative charge, and carbon dots engineered with cationic groups, such as quaternary ammonium, guanidinium or polyamine functionalities, bind electrostatically to those surfaces, destabilizing the lipid bilayer and causing leakage of intracellular contents. Work on positively charged dots derived from tartaric acid and m-aminophenol demonstrated selective killing of Gram-positive bacteria, while super-cationic dots synthesized from spermidine have been formulated as eye drops to treat bacterial keratitis. Evidence also implicates interference with bacterial metabolism: carbon dots have been shown to inhibit enzymes central to glycolysis and peroxidase activity, induce lipid peroxidation measurable by malondialdehyde levels, promote programmed bacterial death, and even trigger transitions in DNA conformation. The review stresses that surface chemistry, not just particle size, is the dominant variable, a conclusion reinforced by quantitative structure-activity relationships that link surface functionalization directly to photo-activated antibacterial potency.

Against biofilms specifically, carbon dots deploy a layered strategy. Preventing initial adhesion is the first line of defense: negatively charged or amphiphilic dots can repel bacterial attachment to surfaces, and coatings incorporating carbon nanodots have produced antibiofilm and anticorrosion surfaces for industrial applications. Once a biofilm has formed, the extracellular polymeric matrix becomes the barrier, and carbon dots have demonstrated the ability to penetrate that matrix, imaging its scaffolds and, in quaternized variants, eradicating the embedded cells with enhanced efficiency. Perhaps most intriguingly, the review documents interference with quorum sensing, the chemical communication system bacteria use to coordinate biofilm formation and virulence. Carbon dots have disrupted acyl-homoserine lactone and autoinducing peptide signaling, undermined the machinery that coordinates collective behavior, and thereby prevented mature biofilm architecture from developing. Combined approaches, including carbon dots grafted with chitosan, papain, silver or gold nanoparticles, and metal-doped formulations using copper or iron, amplify these effects through synergistic oxidative and physical mechanisms.

Synthesis routes shape all of these properties, and the review systematically compares top-down methods, which cleave larger carbon structures such as graphite, carbon nanotubes or activated carbon via electrochemical oxidation, laser ablation or chemical oxidation, with bottom-up approaches that build dots from molecular precursors through hydrothermal, solvothermal, microwave or pyrolytic processing. Top-down routes often yield crystalline graphitic cores with robust photoluminescence, while bottom-up routes offer finer control over dopant incorporation and surface passivation. The choice of precursor, temperature, reaction time and dopant determines the emission color, surface charge, ROS-generating capacity and biocompatibility of the final product. Green synthesis from medicinal plants, sugarcane juice, ginkgo leaves and bacterial biomass has produced multifunctional dots with simultaneous antimicrobial, antioxidant and bioimaging capabilities, and particle size distribution itself has been shown to influence antibacterial strength.

The application landscape the review maps is strikingly broad. In biomedicine, carbon dots have treated infected wounds in hydrogels, eradicated biofilms on medical implants and titanium surfaces, combated bacterial keratitis and pneumonia, and shown low drug-resistance development over prolonged use, a critical advantage where conventional antibiotics rapidly select for resistant strains. In food science, carbon-dot-loaded films and coatings have preserved salmon, avocado and fresh produce by combining antibacterial action with UV shielding and antioxidant activity, while fluorescent aptamer-conjugated dots detect pathogens such as Salmonella and Escherichia coli with high sensitivity. Environmental and sensing applications range from wastewater-treatment membranes and photocatalytic pollutant degradation to fluorescence probes for toxic metal ions, pesticides, antibiotics and bacterial quorum-sensing activity, with emerging theranostic platforms integrating imaging, sensing and therapy in single nanomaterials.

The review does not shy away from the field’s weaknesses. Batch-to-batch consistency in large-scale production remains a persistent stumbling block, since minor variations in precursor composition or reaction conditions can shift surface chemistry and, with it, biological activity. Long-term in vivo biocompatibility and biodistribution data are still limited, and the stability of carbon dots in the complex chemical environments of real infections, wounds and industrial systems requires far more rigorous evaluation. Standardized protocols for characterizing and benchmarking antibacterial performance are also lacking, making cross-study comparisons difficult. Looking forward, the authors identify multifunctional theranostic carbon dots that combine diagnostics, drug delivery and phototherapy, along with structure-guided rational design driven by quantitative structure-activity relationships, as the most promising trajectories. If those challenges can be met, carbon dots may graduate from laboratory curiosity to frontline weapon in the escalating war against antibiotic-resistant bacteria and the biofilms that shelter them.

Subject of Research: Carbon dots as antibacterial and anti-biofilm nanomaterials

Article Title: Carbon dots: a promising antibacterial and anti-biofilm agent

Article References: Li, P., Zhang, S., Yu, X., Chen, J., Xu, Y., Zhang, D., Ke, X., & Li, Z. (2026). Carbon dots: a promising antibacterial and anti-biofilm agent. Journal of Nanoparticle Research, 28(9), Article 239. https://doi.org/10.1007/s11051-026-06759-y

Image Credits: AI Generated

DOI: 10.1007/s11051-026-06759-y

Keywords: carbon dots, antibacterial, anti-biofilm, reactive oxygen species, membrane disruption, quorum sensing, antibiotic resistance, nanomaterials, photodynamic therapy, biofilms, nanomedicine, green synthesis