Tannic acid (TA) is one of the active components in the Galla Chinensis and has various effects, including antioxidant and anti-inflammatory properties. However, research on its antiviral properties remains limited. Here, tannic acid carbon dots (TA-CDs) were prepared as potential antiviral drugs from polyphenol TA under different temperature conditions (180, 200, 220 and 240 °C). Compared to TA alone, TA-CDs exhibited lower cytotoxicity and a tenfold enhanced in antiviral activity. Additionally, the antiviral effects of TA-CDs varied with preparation temperatures, with the best effect observed at 200 °C (CDs-2), reaching a titer of 2.8 orders of magnitude in porcine reproductive and respiratory syndrome virus (PRRSV), mainly due to its relatively higher number of functional groups and smaller particle size. Mechanically, CDs-2 was shown to inhibit PRRSV by targeting the stages of inactivation, adsorption, invasion, replication, and down-regulating reactive oxygen species (ROS) levels. Moreover, CDs-2 exhibited a high inhibitory effect on porcine epidemic diarrhea virus (PEDV), reaching a titer of 7 orders of magnitude. This study reveals the importance of temperature in synthesis of traditional Chinese medicine-derived carbon dots (TCM-CDs) and confirms their potential as antiviral drugs, providing valuable information for development of TCM antiviral drugs.

The conversion of tannic acid into carbon dots enhances its antiviral activities
    Abstract
        Graphical abstract
    1 Introduction
    2 Materials and methods
        2.1 Preparation of tannic acid carbon dots (TA-CDs)
        2.2 Exploratory tests of antiviral activity
        2.3 Exploratory tests of antiviral mechanisms
        2.4 Statistical analysis
    3 Results and dicussion
        3.1 Characterization of TA-CDs
        3.2 TA-CDs reduce cytotoxicity to MARC-145 and Vero cells
        3.3 TA-CDs enhance anti-PRRSV activity
        3.4 TA-CDs inhibit the inactivation, adsorption, invasion, and replication stages of PRRSV lifecycle
        3.5 TA-CDs inhibit ROS production
        3.6 TA-CDs inhibit PEDV proliferation
    4 Conclusion
    Acknowledgements 
    References

• Caifeng Ren(State Key Laboratory of Agricultural Microbiology, College of Resource and Environment, College of Chemistry, Huazhong Agricultural University, Wuhan 430070, People’s Republic of China)
• Jiangong Liang(State Key Laboratory of Agricultural Microbiology, College of Resource and Environment, College of Chemistry, Huazhong Agricultural University, Wuhan 430070, People’s Republic of China) Corresponding author
• Shaobo Xiao(State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Key Laboratory of Preventive Veterinary Medicine in Hubei Province, Huazhong Agricultural University, Wuhan 430070, People’s Republic of China)
• Yanrong Zhou(State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Key Laboratory of Preventive Veterinary Medicine in Hubei Province, Huazhong Agricultural University, Wuhan 430070, People’s Republic of China)
• Liurong Fang(State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Key Laboratory of Preventive Veterinary Medicine in Hubei Province, Huazhong Agricultural University, Wuhan 430070, People’s Republic of China)
• Yuan Wu(College of Chemistry, Huazhong Agricultural University, Wuhan 430070, People’s Republic of China)