Exploring Low-Power Single-Pulsed Laser-Triggered Two-Photon Photodynamic/Photothermal Combination Therapy Using a Gold Nanostar/Graphene Quantum Dot Nanohybrid

[Image: see text] Combined photodynamic/photothermal therapy (PDT/PTT) has emerged as a promising cancer treatment modality due to its potential synergistic effects and identical treatment procedures. However, its clinical application is hindered by long treatment times and complicated treatment operations when separate illumination sources are required. Here, we present the development of a new nanohybrid comprising thiolated chitosan-coated gold nanostars (AuNS-TCS) as the photothermal agent and riboflavin-conjugated N,S-doped graphene quantum dot (Rf-N,S-GQD) as the two-photon photosensitizer (TP-PS). The nanohybrid demonstrated combined TP-PDT/PTT when a low-power, single-pulsed laser irradiation was applied, and the localized surface plasmon resonance of AuNS was in resonance with the TP-absorption wavelength of Rf-N,S-GQD. The TCS coating significantly enhanced the colloidal stability of AuNSs while providing a suitable substrate to electrostatically anchor negatively charged Rf-N,S-GQDs. The plasmon-enhanced singlet oxygen ((1)O(2)) generation effect led to boosted (1)O(2) production both extracellularly and intracellularly. Notably, the combined TP-PDT/PTT exhibited significantly improved phototherapeutic outcomes compared to individual strategies against 2D monolayer cells and 3D multicellular tumor spheroids. Overall, this study reveals a successful single-laser-triggered, synergistic combined TP-PDT/PTT based on a plasmonic metal/QD hybrid, with potential for future investigation in clinical settings.