Carbon dot nanozymes: From synthetic control to catalytic mechanisms and sensing applications

Carbon dot (CD)-based nanozymes have become promising substitutes to natural enzymes in high-performance analytical detection systems, due to their high-water solubility, tunable surface chemistry, and their ability to produce multiple signaling outputs. It has been shown that CDs have a variety of enzyme-mimetic activities, such as peroxidase (POD), oxidase (OXD), and superoxide dismutase (SOD)-like activities, and can be used in bioassays and environmental monitoring. Although such progress has been made, there is still no detailed theoretical framework that explains the origins of their catalytic activity and the mechanisms that underlie sensing selectivity, thus restricting the rational design and optimization of CD-based nanozymes. This is a systematic review of the impact of precursor selection, reaction conditions, and doping strategies on the surface functional groups, defect structures, and metal active centers of CDs. It also explains how these structural features work synergistically to regulate electron transfer processes and active site formation. Furthermore, the review suggests that interfacial noncovalent interactions are the main determinants of the sensing selectivity of CD nanozymes, which is accompanied by molecular recognition processes and energy-level complementation. Recent advances in multimodal signaling strategies to detect complex systems are also mentioned. Lastly, the present issues and future outlooks in the controlled construction and sensing uses of CDs are also pointed out, which can be useful in the rational design and practical use of these new nanozymes.