Carbon quantum dots (CQDs) are novel nanocarbon materials and widely used nanoparticles. They have gradually gained popularity in various fields due to their abundance, inexpensive cost, small size, ease of engineering, and distinct properties. To determine the antibacterial activity of metal-doped CQDs (metal-CQDs) containing Fe, Zn, Mn, Ni, and Co, we chose Staphylococcus aureus as a representative Gram-positive strain and Escherichia coli as a representative Gram-negative bacterial strain. Paper disc diffusion tests were conducted for the qualitative results, and a cell growth curve was drawn for quantitative results. The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and IC50 were measured from cell growth curves. As a result, all of the metal-CQDs showed toxicity against both Gram-positive and Gram-negative bacteria. Furthermore, Gram-negative bacteria was vulnerable to metal-CQDs than Gram-positive bacteria. The toxicity differed concerning the type of metal-CQDs; Mn-CQDs exhibited the highest efficacy. Hence, this study suggested that CQDs can be used as new nanoparticles for antibiotics.

Determination of the antibacterial activity of various metal-doped carbon quantum dots
    Abstract
    1 Introduction
    2 Materials and methods
        2.1 Preparation of metal CQDs
        2.2 Paper disc diffusion test for observation of visible inhibition
        2.3 Cell growth curves for the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC)
        2.4 Determination of the IC50
    3 Results
        3.1 Characterization of metal-CQDs
        3.2 Paper disc diffusion tests for observation of visible inhibition
        3.3 Cell growth curves for MIC, MBC, and IC50
    4 Discussion
    5 Conclusion
    Acknowledgements 
    References

• Hyojin Jeong(Department of Bioengineering and Biotechnology, College of Engineering, Chonnam National University, Gwangju 61186, Republic of Korea)
• Seunghyeon Jo(Department of Bioengineering and Biotechnology, College of Engineering, Chonnam National University, Gwangju 61186, Republic of Korea)
• Seulah Yang(Department of Bioengineering and Biotechnology, College of Engineering, Chonnam National University, Gwangju 61186, Republic of Korea)
• Songhee Lee(Interdisciplinary Program of Bioenergy and Biomaterials Graduate School, Chonnam National University, Gwangju 61186, Republic of Korea)
• Subramani Surendran(Hydrogen Energy Technology Laboratory, Korea Institute of Energy Technology (KENTECH), Naju 58330, Jeollanamdo, Republic of Korea)
• Duong Nguyen Nguyen(School of Chemical Engineering, Sungkyunkwan University (SKKU), 2066 Seobu‑Ro, Jangan‑Gu, Suwon 16419, Republic of Korea)
• Unbeom Baeck(School of Chemical Engineering, Sungkyunkwan University (SKKU), 2066 Seobu‑Ro, Jangan‑Gu, Suwon 16419, Republic of Korea)
• Jung Kyu Kim(School of Chemical Engineering, Sungkyunkwan University (SKKU), 2066 Seobu‑Ro, Jangan‑Gu, Suwon 16419, Republic of Korea)
• Uk Sim(Hydrogen Energy Technology Laboratory, Korea Institute of Energy Technology (KENTECH), Naju 58330, Jeollanamdo, Republic of Korea, Research Institute, NEEL Sciences, INC., Naju, Republic of Korea)
• Sooim Shin(Department of Bioengineering and Biotechnology, College of Engineering, Chonnam National University, Gwangju 61186, Republic of Korea, Interdisciplinary Program of Bioenergy and Biomaterials Graduate School, Chonnam National University, Gwangju 61186, Republic of Korea) Corresponding author