Two-dimensional Pd-based nanomaterials for bioapplications

Noble metal nanomaterials have been extensively explored in cancer diagnostic and therapeutic applica- tions owing to their unique physical and chemical properties, such as facile synthesis, straightforward surface functionalization, strong photothermal effect, and excellent biocompatibility. Herein, we summa- rize the recent development of two-dimensional （2D） Pd-based nanomaterials and their applications in cancer diagnosis and therapy. Different synthetic strategies for Pd nanosheets and the related nanostruc- tures, including Pd@Au, Pd@Ag nanoplates and mesocrystalline Pd nanocomlla, are first discussed. Together with their unique properties, the potential bioapplications of these 2D Pd nanomaterials are then demonstrated. With strong absorption in near-infrared （NIR） region, these nanomaterials have great potentials in cancer photothermal therapy （PTr）. They also readily act as contrast agents in photoacoustic （PA） imaging or X-ray computed tomography （CT） to achieve image-guided cancer therapy. Moreover, significant efforts have been devoted to studying the combination of PTr and other treatment modalities （e.g., chemotherapy or photodynamic therapy） based on Pd nanomaterials. The remarkable synergistic or collaborative effects to achieve better therapeutic efficacy are discussed as well. Additionally, the biosaf- ety of 2D Pd-based nanomaterials in vitro and in vivo was evaluated. Finally, challenges for the applica- tions of Pd-based nanomaterials in cancer diagnosis and therapy, and future research prospects are highlighted.

Effect of glutathione on in vivo biodistribution and clearance of surface-modified small Pd nanosheets

Plasmonic Pd nanosheets have been emerging as promising materials for application in near-infrared(NIR) photothermal therapy(PTT) of cancer. However, animal in mice studies indicated that the original synthesized poly(vinylpyrrolidone)(PVP)-protected small Pd nanosheets(Pd-PVP) and some further surface-modified small Pd nanosheets such as Pd-PEG(SH) easily accumulated in reticuloendothelial system(RES) organs(liver, spleen, etc.) and were difficult to be cleared from these organs quickly. In the work, we surprisingly found that glutathione(GSH) could promote the clearance of surface-modified small Pd nanosheets(e.g. Pd-PVP, Pd-PEG(SH) and Pd-GSH) from the RES organs efficiently. The effects of GSH on the biodistribution and clearance of different surface-modified Pd nanosheets were investigated. Our results indicated that these surface-modified Pd nanosheets with or without GSH added caused no morbidity at target primary organs, and GSH can promote the clearance of different surface-modified Pd nanosheets in the order of Pd-PVP≈Pd-PEG(SH)>Pd-GSH. This study suggests that glutathione could be an attractive reagent for promoting nanomaterials eliminated from the reticuloendothelial systems(RES).