Near-infrared (NIR) dyes functionalized magnetic nanoparticles (MNPs) have been widely applied in magnetic resonance imaging (MRI), NIR fluorescence imaging, drug delivery, and magnetic hyperthermia. However, the stability of MNPs and NIR dyes in water is a key problem to be solved for long-term application. In this study, a kind of superstable iron oxide nanoparticles was synthesized by a facile way, which can be used as T1 and T2 weighted MRI contrast agent. IR820 was grafted onto the surface of nanoparticles by 6-amino hexanoic acid to form IR820-CSQ-Fe conjugates. Attached IR820 showed increased stability in water at least for three months and an enhanced ability of singlet oxygen production of almost double that of free dyes, which will improve its efficiency for photodynamic therapy. Meanwhile, the multispectral optoacoustic tomography (MSOT) and NIR imaging ability of IR820-CSQ-Fe will greatly increase the accuracy of disease detection. All of these features will broaden the application of this material as a multimodal theranostic platform.

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