###### Abstract  
Carbon quantum dots (CQDs) are known for their intriguing optical properties, low toxicity, and high biocompatibility, which make them promising for biomedical applications. In this study, CQDs were synthesized by subjecting orange juice to microplasma as a carbon source at atmospheric pressure and low temperatures. The resulting CQDs exhibited a narrow size distribution, with an average diameter of approximately 4.5 nm and a pH value of 5.67. These CQDs exhibited strong blue emission characteristics. The antibacterial properties of the CQDs against _Escherichia coli_ (_E. coli_) strains were evaluated using minimum inhibitory concentration assays. The study revealed that an effective inhibition of _E. coli_ was achieved at a minimum inhibitory concentration of 0.1 ppm, while the minimum bactericidal concentration for this bacterial strain was 1 ppm, resulting in an average antibacterial efficacy of 57%. Notably, the antibacterial effects of the CQDs were observed without the need for additional light or oxidants, demonstrating the applicability of CQDs in combating bacterial strains. carbon quantum dots; plasma; antibacterial; _Escherichia coli_; bacteria strains  
methods [1, 5]. Their exceptional fluorescence and minimal cytotoxicity make them ideal for optoelectronics, sensing, and photocatalysis [6, 7]. In the biomedical realm, CQDs have gained recognition for diverse theranostic applications like cellular imaging, drug delivery, and antibacterial activity [1, 8, 9]. Structured as nanoparticles, these minuscule carbon-based materials exhibit versatile traits applicable across domains encompassing biomedical imaging, drug delivery, sensors, catalysis, electronics, energy storage, water purification, nanocomposite materials, and photocatalysis. The adaptability of CQDs to nanoparticle forms positions them as promising candidates in nanotechnology-driven systems. However, transitioning from theoretical potential to practical application poses significant challenges. Addressing scalable production, synthesis reproducibility, and long-term safety concerns is vital for realizing the extensive potential of CQDs. This emphasizes the crucial need for innovation, scalability, reproducibility, and safety considerations across various scientific disciplines and industrial sectors [10]. Additionally, CQDs can be categorized into two distinct types, namely hydrophilic and hydrophobic CQDs [11]. Hydrophilic CQDs, with an affinity for water, excel in aqueous applications like biomedicine and water purification [12]. In contrast, hydrophobic CQDs, repelling water, find utility in non-aqueous environments for applications such as photothermal therapy, energy storage, and surface coatings [13]. Understanding their specific properties enables targeted applications across scientific and industrial domains. Diverse approaches have been employed for the synthesis of CQDs, encompassing both (i) bottom-up methods, such as hydrothermal and solvothermal syntheses, microwave synthesis, and plasma treatments, and (ii) top-down techniques, including electrochemical exfoliation, laser ablation, and chemical oxidation [1, 14, 15]. However, it is essential to acknowledge that some of these methods involve the use of strong acids, high processing temperatures, and complex multi-step processes, which can pose disadvantages when scaling up production or considering medical applications, potentially introducing hazardous effects due to the presence of toxic chemicals. As a result, there remains a pressing need for greener chemistry routes in the synthesis of nanoparticles, aiming for eco-friendly and cost-effective production. Notably, recent efforts have explored the use of natural precursors, such as juice from Citrus media [16], orange juice [17], honey [18], and grape seeds [8], for CQD synthesis. These products derived from natural sources are considered \"green\" and cost-effective, making them suitable for bulk product development.