Carbon dots as light-responsive oxidase-like nanozyme for colorimetric detection of total antioxidant capacity in fruits

Evaluation of total antioxidant capacity (TAC) in fruits is essential for dietary guidance and health monitoring. Here, we have exploited light-response carbon dots (CDs) as oxidase-like nanozyme to determine the TAC of fruits. The CDs possess excellent oxidase-like activity with light stimulation due to the accelerated intramolecular charge transfer caused by abundant electron donating/drawing groups in precursors. The scavenger experiment reveals that the catalytic intermediate could be hydroxyl radical, which can oxidize the colorimetric substrate. With the introduction of antioxidants, the oxidization of colorimetric substrate will be alleviated due to the scavenging of this intermediate by antioxidants. Based on this, we have successfully detected three antioxidants and obtained TAC of fruits with desirable results. This work affords a rapid, cost-effective and convenient analysis tool for TAC, as well as building a strong bridge between CDs and the development of photo-responsive oxidase-like nanozymes.