NIR-II window absorbing graphene oxide-coated gold nanorods and graphene quantum dot-coupled gold nanorods for photothermal cancer therapy

The graphene-based materials have been used as a potential coating material for nanoparticles due to their excellent passivation. Herein, we report for the first time the colloidal stability, photothermal profile, thermal stability, cytotoxicity, and photo-cytotoxicity of graphene quantum dots (GQDs) coupled with the second infrared window (NIR-II) absorbing gold nanorods (AuNRs/GQDs) and compare it to graphene oxide (GO)-coated NIR-II absorbing AuNRs (AuNRs/GO). The composites were achieved by electrostatic interaction of the GO or GQDs with AuNRs. The results revealed that (i) AuNRs/GQDs were more stable in the aqueous phosphate buffer and cell culture media than AuNRs/GO and AuNRs; (ii) GO enhanced the photothermal efficiency of the AuNRs, whereas GQDs reduced it; (iii) GQDs enhanced the photothermal stability of AuNRs than GO; (iv) both AuNRs/GO and AuNRs/GQDs were biocompatible with mouse colon carcinoma (C26) cell lines and malignant fibrous histiocytoma-like, expressing a fusion of the luciferase and enhanced green fluorescent protein genes (KM-Luc/GFP) cell lines; and (v) photo-cytotoxicity of AuNRs/GO and AuNRs/GQDs conducted against C26 cell lines showed significantly improved cell death compared to laser irradiation alone; however, AuNRs/GO exhibited high photo-toxicity than AuNRs/GQDs. This study shows that AuNRs/GO and AuNRs/GQDs composites possess unique properties to improve AuNRs and be utilised in photothermal applications.