<p>Carbon dots (CDs), as an emerging class of carbon-based nanomaterials, have attracted extensive attention owing to their tunable surface chemistry, strong photoluminescence, high stability, and excellent biocompatibility. Unlike conventional semiconductor quantum dots, whose properties are primarily determined by rigid crystal lattices, the key characteristics of CDs are mainly established during the synthesis process; the choice of precursors, reaction conditions, and post-synthetic treatments can directly influence their particle size, emission behavior, and surface states. At present, CDs have demonstrated broad application potential across multiple fields. In information security, they have been exploited for the construction of unclonable physical anti-counterfeiting tags. In the energy and environmental sectors, CDs can be employed in the development of efficient photothermal and thermoelectric devices, as well as for pollutant monitoring and photocatalytic degradation. In biomedicine, as a major application area, CDs have enabled diversified developments ranging from cellular imaging and biosensing to the regulation of plant growth. This review systematically summarizes recent advances in the synthesis of CDs, provides an in-depth analysis of various controllable preparation methods, and discusses their multifunctional protective roles in antioxidant, antibacterial, and photoprotective applications.</p> Graphical Abstract <p></p>