Biocompatible Graphene Quantum Dots via Gamma Irradiation and L-Cysteine Modification

Abstract

Graphene quantum dots (GQDs) are a newly synthesized type of quantum dots that have unique physicochemical properties, making them promising for biomedical applications. Unlike inorganic quantum dots, GQDs are easily produced, highly fluorescent, resistant to photo-bleaching, soluble, and biocompatible [1]. The functionalization of electrochemically synthesized GQDs was achieved by using gamma irradiation, amino acid L-cysteine as a donor of S and N heteroatoms, and IPA alcohol as a radical scavenger [2]. XPS analysis confirmed the presence of S and N atoms in the modified samples which indicates the successful modification of the material. The best results were observed in a sample irradiated with a dose of 25 kGy, where the atomic percentages of nitrogen and sulfur were 1.15 at% and 1.14 at%, respectively. Gamma irradiation altered the NMR signals for carbonyl protons and OH groups, but the aromatic structure remained intact, as confirmed by the 13C spectrum. Antibacterial activity was tested on a sample irradiated with 25 kGy, and after being irradiated under a blue lamp for 60 minutes, mild antibacterial activity was observed against Staphylococcus aureus, Enterococcus faecium, and Escherichia coli. The same sample after 6 hours under a blue lamp showed mild antibacterial activity also for MRSA and Acinetobacter baumannii. The modified GQDs samples showed mild photo-induced antibacterial activity against several bacterial strains with no changes observed in the absence of light suggesting that this method of GQD modification could be a promising approach for developing biocompatible nanomaterials.