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Carbon dots (CDs) are semiconductor materials with sizes ranging from 2 to 10 nm. Among these CDs, nickel CDs (Ni@CDs) materials have piqued researchers' curiosity in the past years due to their specific properties, such as strong catalytic activity, good stability, great hydrophilicity, and high oxidation states. Several synthetic pathways exist for the synthesis of Ni@CDs, such as hydrothermal method, microwave irradiation, green synthesis, pyrolytic decomposition, precipitation method, and electrochemical route. These Ni@CDs have shown application in charge transfer, excellent thermodynamic stability, luminescent properties, high chemical and photo-stability, opto-electronic devices, catalysis, sensing, and drug delivery. In this review, various synthetic methods had been explored extensively along with their numerous applications.

Metal doped carbon dots (CDs) have been extensively studied due to their tunable and strong fluorescence emission properties, which make them applicable for sensing, organic catalysis, optronics, and biomedicine. This has attracted the attention of many researchers to develop transition metal-doped CDs. In this article, we have discussed various syntheses and applications of copper doped CDs (Cu@CDs). We have mainly focused on copper because of its various advantages, such as low cost, low toxicity, natural abundance, and ability to show 0-III oxidation states which give them access to show both one and two-electron processes. Majorly, we have briefed on the recent progress in the synthesis, functionalization, and applications of Cu@CDs using chemical reduction, hydrothermal, solvothermal, thermolysis, and green synthesis from various chemical and natural carbon pre-cursors. Afterward, we have discussed their applications in analyte detection and sensing, organic catalysis, anti-microbial activity, bio-imaging, and cancer therapy.