The antioxidant properties of green carbon dots: a review

Abstract

The generation of reactive species and their derivatives, whether in the human body or in the food systems, contributes to various human diseases and compromises food quality. Unfortunately, both natural and synthetic antioxidants have specific limitations. Green chemistry-derived carbon dots offer a promising solution in this regard. Here we review the antioxidant activity of green synthesized carbon dots. The review commences with an overview of carbon dots, their properties, and the top-down and bottom-up synthesis approaches, along with their merits and drawbacks. Furthermore, the importance of the green chemistry concept is highlighted. The role of different functional groups in carbon dots attributed to their antioxidant activity is emphasized. Subsequently, the review elucidates several methods commonly utilized to evaluate the antioxidant activity of carbon dots together with a discussion on various oxidative and non-oxidative stress markers. The review compiles a variety of ex vivo, in vitro, and in vivo studies underscoring the antioxidant activity of pristine and doped carbon dots. Among all studies, the hydrothermal method was observed to be a popular synthesis approach. Out of 87 studies, 38 exclusively assessed the 2,2-diphenyl-1-picrylhydrazyl-scavenging properties of pristine and doped carbon dots with half-maximum effective concentration values ranging from 2.7 to 524 μg mL⁻¹. The subsequent studies recorded the scavenging of other radicals alongside 2,2-diphenyl-1-picrylhydrazyl, with 18, 14, 10, 5, and 2 studies demonstrating the scavenging efficacy of carbon dots for hydroxyl, 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid), superoxide, hydrogen peroxide, and nitric oxide radicals, respectively. Furthermore, 18 studies reported the antioxidant property of carbon dots in cell, animal, and vertebrate models by modulating oxidative stress markers and upregulating the expressions of various antioxidant enzymes. The review also highlights the prooxidant nature of green carbon dots briefly. Finally, the paper delves into the practical applications of carbon dots in the food, agricultural, and environmental sectors.