Antimicrobial Amino-Functionalized Nitrogen-Doped Graphene Quantum Dots for Eliminating Multidrug-Resistant Species in Dual-Modality Photodynamic Therapy and Bioimaging under Two-Photon Excitation

Developing a nanomaterial, for use in highly efficient dual-modality two-photon photodynamic therapy (PDT) involving reactive oxygen species (ROS) generation and for use as a two-photon imaging contrast probe, is currently desirable. Here, graphene quantum dots (GQDs) doped with nitrogen and functionalized with an amino group (amino-N-GQDs) serving as a photosensitizer in PDT had the superior ability to generate ROS as compared to unmodified GQDs. Multidrug-resistant (MDR) species were completely eliminated at an ultralow energy (239.36 nJ pixel-1) through only 12 s two-photon excitation (TPE) in the near-infrared region (800 nm). Furthermore, the amino-N-GQDs had an absorption wavelength of approximately 800 nm, quantum yield of 0.33, strong luminescence, an absolute cross section of approximately 54 356 Göeppert-Mayer units, a lifetime of 1.09 ns, a ratio of the radiative to nonradiative decay rates of approximately 0.49, and high two-photon stability under TPE. These favorable properties enabled the amino-N-GQDs to act as a two-photon contrast probe for tracking and localizing analytes through in-depth two-photon imaging in a three-dimensional biological environment and concurrently easily eliminating MDR species through PDT.