Green PEGylation of Graphene Oxide via Diels-Alder Chemistry in Deep Eutectic Solvents for pH-Responsive Doxorubicin Delivery.

Graphene oxide (GO), a two-dimensional carbon nanomaterial, exhibits a large surface area, rich oxygen-containing functionalities, and favorable aqueous dispersibility, making it a suitable platform for drug delivery. However, traditional covalent modification strategies frequently involve multistep procedures or the use of hazardous organic solvents. In this study, GO was functionalized via a novel green strategy: Diels-Alder (DA) cycloaddition of maleic anhydride (MA) utilizing deep eutectic solvents (DESs) as a sustainable reaction medium. The resulting GO-PEG nanocarriers, formed through subsequent esterification with poly(ethylene glycol) lithium alkoxide, were thoroughly characterized by FTIR, Raman spectroscopy, XRD, and TGA. This DES-based approach distinguishes itself from prior DA functionalizations by offering an environmentally benign pathway that maintains high grafting efficiency without the need for toxic volatile media. The optimized DOX/GO-PEG nanohybrids exhibited a high doxorubicin (DOX) loading capacity of 128.4 wt.% at a feed ratio of 150:1 (DOX/GO-PEG, w/w) and demonstrated pH-responsive drug release-77.3% at pH 5.0 and 36.3% at pH 7.4 after 72 h. Cytotoxicity studies showed that GO-PEG exhibited negligible toxicity to HEK293 cells, whereas DOX/GO-PEG induced potent, dose-dependent cytotoxicity in HeLa cancer cells. Confocal imaging confirmed DOX nuclear accumulation in treated HeLa cells. This study provides a first-time demonstration of DES-mediated DA PEGylation on GO, establishing a high-efficiency and eco-friendly framework for advanced nanocarrier synthesis.