Both photothermal therapy (PTT) and chemodynamic therapy (CDT) are designed to focus their antitumor effect on only the tumor site, thereby minimizing unwanted severe damage to healthy tissue outside the tumor. However, each monotherapy is limited in achieving complete tumor eradication, resulting in tumor recurrence. The combination of multiple therapies may help to overcome the limitations of single therapy, improve the chances of complete tumor eradication, and reduce the risk of recurrence. Here, we report a novel multifunctional carrier-free nanoparticle, namely Mn-TPP@ICG, prepared through the self-assembly of ICG and 5,10,15,20-Tetraphenyl-21H,23H-porphine manganese (III) chloride (Mn-TPP). The prepared Mn-TPP@ICG allowed dual-mode imaging in the form of magnetic resonance imaging (MRI) and near-infrared (NIR) fluorescence imaging, as well as combination therapy in the form of CDT and PTT. In vitro experiments revealed that Mn-TPP@ICG nanoparticles can enable CDT by converting intratumoral hydrogen peroxide (H2O2) to highly cytotoxic hydroxyl radicals (·OH) and PTT through photothermal conversion, resulting in a strong synergistic antitumor effect. Furthermore, in vivo experiments revealed that CDT and PTT with Mn-TPP@ICG nanoparticles effected a synergistically enhanced therapeutic effect in 4T1 tumor-bearing mice, significantly inhibiting tumor growth compared with monomodal treatments with no treatment, only CDT, or only PTT. Lastly, imaging experiments unveiled the exceptional capability of Mn-TPP@ICG nanoparticles in enabling fluorescence imaging and high-resolution MRI upon their intravenous administration. Thus, a meaningful carrier-free nanoparticle strategy for the synergistic combination of CDT and PTT was provided in our study, broadening the applications of nanotheranostics.Copyright © 2025 Elsevier B.V. All rights reserved.