Crossover between Anti- and Pro-oxidant Activities of Graphene Quantum Dots in the Absence or Presence of Light

Abstract

Graphene quantum dots (GQDs), zero-dimensional carbon materials displaying excellent luminescence properties, show great promise for medical applications such as imaging, drug delivery, biosensors, and novel therapeutics. A deeper understanding of how the properties of GQDs interact with biological systems is essential for these applications. Our work demonstrates that GQDs can efficiently scavenge a number of free radicals and thereby protect cells against oxidative damage. However, upon exposure to blue light, GQDs exhibit significant phototoxicity through increasing intracellular reactive oxygen species (ROS) levels and reducing cell viability, attributable to the generation of free radicals under light excitation. We confirm that light-induced formation of ROS originates from the electron-hole pair and, more importantly, reveal that singlet oxygen is generated by photoexcited GQDs via both energy-transfer and electron-transfer pathways. Moreover, upon light excitation, GQDs accelerate the oxidation of non-enzymic anti-oxidants and promote lipid peroxidation, contributing to the phototoxicity of GQDs. Our results reveal that GQDs can display both anti- and pro-oxidant activities, depending upon light exposure, which will be useful in guiding the safe application and development of potential anticancer/antibacterial applications for GQDs.

Graphene quantum dot based charge‐reversal nanomaterial for nucleus‐targeted drug delivery and efficiency controllable photodynamic therapy

“…To measure the PDT efficacy, the ROS dyes including DCFDA and DHE were used to image the generation of ROS . As shown in the second row of the image panel in Figure , strong green DCFDA fluorescence was observed in MDA‐MB‐231 cells incubated with 5‐μg/mL N‐GQD‐DOX and N‐GQD‐DOX‐APTES both after LED irradiation for 20 minutes.…”

“…Photodynamic therapy (PDT) is a clinically approved therapeutic modality used for the treatment of neoplastic diseases . In PDT, a photosensitizing agent under the illumination of light at proper wavelengths produces reactive oxygen species (ROS) such as singlet oxygen by energy transfer from light excited photosensitizer molecules to oxygen molecules . The generated ROS can be used to selectively damage a target tissue region because light illumination can be precisely controlled .…”

Selenium‐Doped Carbon Quantum Dots for Free‐Radical Scavenging

“…Thestrong ESR signals indicated the formation of the DEMPO/COH adduct when the H 2 O 2 solution was exposed to ultraviolet light. [13] However,t he ESR signals of the DEMPO/COH adduct disappeared when Se-CQDs were added into the solution. Ther esults suggested that the Se-CQDs had strong COH-scavenging activity.However,adifferent and weak ESR signal appeared when the Se-CQDs were exposed to UV light, and no signals were observed without light exposure.W especulate that the new free radical signals belong to the DEMPO/CNH 2 adduct originating from the amino groups in the Se-CQDs.…”

Graphene Quantum Dots Protect against Copper Redox-Mediated Free Radical Generation and Cardiac Cell Injury

“…On the other hand, the electrochemical and redox properties of GQDs might make them useful in protecting against oxidative stress, a pathophysiological process widely implicated in human diseases [3, 4]. Indeed, early work reported potential free radical-scavenging activities of GQDs in cell-free systems [5]. In the present study, we report for the first time that GQDs potently protected against copper redox-mediated free radical generation and cardiac cell injury.…”

“…Indeed, an early study indicated that the electron transfer from GQDs to a copper complex enhanced the nuclease activity of the copper complex [15]. In addition, as noted earlier, GQDs are redox active, possessing potential antioxidant activities [5]. Hence, it is not surprising that GQDs could reduce Cu(II) to Cu(I).…”