Ag-Conjugated graphene quantum dots with blue light-enhanced singlet oxygen generation for ternary-mode highly-efficient antimicrobial therapy

Abstract

The increasing prevalence of antibiotic resistance highlights the need for new antibacterial drugs and, in particular, the development of alternative approaches such as photodynamic therapy (PDT) and photothermal therapy (PTT) to manage this growing issue. In the present study, a broad-spectrum antibacterial system was produced in which Ag nanoparticle-conjugated graphene quantum dots (GQD–AgNP) were utilised as a blue light-enhanced nanotherapeutic for efficient ternary-mode antimicrobial therapy. The successful conjugation of AgNPs onto the surface of GQDs can significantly improve the production of reactive oxygen species in light-activatable GQDs and the transformation of light energy to hyperthermia with high efficiency. There was a remarkable increase in the sample temperature of nearly 40 °C via photoexcitation after only 10 min of 450 nm laser exposure (14.2 mW cm⁻²). The hybrids exhibited much more efficient bactericidal capability against both Gram-negative and Gram-positive bacteria compared with GQDs alone, using 450 nm light irradiation. This is likely a consequence of their enhanced PDT, concomitant PTT, and the synergistic function of AgNPs. The antibacterial mechanism of the new-style nanocomposites was found to irreversibly destroy the bacterial membrane structure, leading to the leaking out of the cytoplasmic contents and the death of the bacteria. At low doses, the biocompatible GQD–AgNP hybrids promoted healing in bacteria-infected rat wounds, with negligible adverse impact to the normal tissue, indicating a promising future for combined photodynamic and photothermal antibacterial applications in clinical medicine.