The serendipitous uncovering of carbon dot (CQDs) as budding candidate of carbonaceous nanomaterial has become now one of the hot topics in the research of material science and technology. The unique features of CQDs such as photo-physical properties, excellent biocompatibility, ease of synthesis, good aqueous dispersity, high chemical stability, and accessible functional groups for further modification make them one of the promising competitors in biological, photonic and energyrelated applications. Although some review articles on CQDs have been published, they typically cover all areas of CQDs applications, and no particular evaluation on the advancement of doped CQDs (D-CQDs) has been reported so far. In this review, we demonstrated characteristic features of D-CQDs focusing on doping strategies, discussion on recently adopted various synthesis processes, its applications and its qualitative comparison with each other. The recently developed concept on understanding the structure and optical properties of D-CQDs are also briefly described followed by their application on various fields primarily concentrated on bio-imaging and sensing applications. We also speculate its use in a variety of intriguing fields and its perspectives in near future.

    Abstract
        Graphical abstract
    1 Introduction
    2 Doping strategies of CQDs
        2.1 Nitrogen (N) doping
        2.2 Sulphur (S) doping
        2.3 Phosphorus (P) doping
        2.4 Boron (B) doping
        2.5 Heteroatom co-doping strategies
    3 Different synthetic methods of CQDs
        3.1 Arc discharge method
        3.2 Microwave assisted synthesis
        3.3 Hydrothermal method
        3.4 Combustion route or pyrolysis method
        3.5 Laser ablation
        3.6 Acidic oxidation
        3.7 Electrochemistry method
        3.8 Sonochemical synthesis
    4 Structure of CQDs
    5 Properties of CQDs
    6 Applications of CQDs
        6.1 Biosensing applications
        6.2 Chemical sensing
        6.3 Bio-imaging application
        6.4 Catalytic applications
        6.5 Others applications
    7 Challenges and outlooks
    Acknowledgements 
    References

• Trisita Ghosh(Rubber Technology Centre, Indian Institute of Technology)
• Tushar Kanti Das(Rubber Technology Centre, Indian Institute of Technology)
• Poushali Das(Bar‑Ilan Institute for Nanotechnology and Advanced Materials (BINA), Department of Chemistry, Bar-Ilan University)
• Pallab Banerji(Materials Science Centre, Indian Institute of Technology)
• Narayan Ch. Das(Rubber Technology Centre, Indian Institute of Technology)