Development of Pd-Loaded Hf-Based Metal–Organic Framework as a Dual-Modal Contrast Agent for Photoacoustic Imaging and Computed Tomography

Noninvasive cancer imaging significantly improves diagnostics by providing comprehensive structural and functional information about tumors. Herein, we explored palladium nanoparticles loaded hafnium-based metal-organic framework (MOF) (Hf-EDB), i.e., Pd@Hf-EDB as an efficient dual modal contrast agent for computed tomography (CT) and photoacoustic imaging (PAI). The synergistic collaborations between (i) high-Z element Hf-based MOF with superior X-rays absorbing capabilities, (ii) H₂EDB linkers with special π-donation and π-acceptor characteristics capable of strongly anchoring noble metals, and (iii) Pd nanoparticles with broad absorption in the UV to near-infrared (NIR) regions due to strong interband transition are ideal for implementation in CT and PAI. The successful synthesis of Pd@Hf-EDB nanoparticles was confirmed through morphology, crystallinity, and compositional characterizations using X-ray diffraction, SEM, TEM, DLS, and EDS. Soft X-ray tomography verified cellular uptake via phagocytosis of Pd@Hf-EDB by BxPC-3 tumor cells. In-vitro experiments revealed superior CT imaging performance of Pd@Hf-EDB over traditional molecular contrast agents like Iohexol. Broad absorption range in the UV-vis/NIR regions and superior PAI capabilities of Pd@Hf-EDB relative to gold nanorods are reported. Furthermore, the in vivo xenograft model demonstrated significant contrast enhancements near the tumor, highlighting the excellent PAI and CT capabilities of the synthesized Pd@Hf-EDB.