Fig. 1. (a) Synthesis route of CQDs from carbon source of carrots through hydrothermal method, reprinted with permission from ref. 78, copyright 2018 Elsevier Ltd., (b) synthesis of CQDs from the pyrolytic residue by chemical oxidation, when the Cu²⁺ ions are present in the solution, the fluorescence quenches, reprinted with permission from ref. 79, copyright 2018 Elsevier Ltd., (c) synthesis of CQDs from carbonization of polyacrylamide chains by formation a microemulsion. Reprinted with permission from ref. 80, copyright 2013 American Chemical Society.