Immune therapy based on programmed death-ligand 1 (PD-L1) is widely used to treat human tumors. The current strategies to improve immune checkpoint blockade therapy fail in rescuing increased expression of PD-L1 in tumor issues. Here, we for the first time synthesized the metal–organic framework (MOF) nanocrystals of rare-earth element dysprosium (Dy) coordinated with tetrakis(4-carboxyphenyl) porphyrin (TCPP), which show well-defined two-dimensional morphologies. The MOF nanocrystals of Dy-TCPP could apparently reduce PD-L1 expression in tumor cells both in vitro and in vivo, and therefore display effective tumor treatment through immune therapy without any immune checkpoint inhibitor drugs. Considering the sensitivity of TCPP ligand toward ultrasound, the prepared Dy-TCPP can also realize sonodynamic therapy (SDT) besides immune therapy. In addition, the Dy-TCPP nanocrystals can efficiently obtain T₂-weight magnetic resonance imaging (MRI) of tumor sites. Our study provides the Dy-TCPP nanocrystals as promising diagnostic MRI-guided platforms for the combined treatment on tumors with SDT and immune therapy. Moreover, this strategy succeeds in reducing the elevated expression of PD-L1 in tumor cells, which might serve as a novel avenue for tumor immunotherapy in future.

Oxygen evolution reaction (OER) still suffers from the bottleneck in electrocatalytic water splitting. Herein, in virtue of volcano plots drawn by theoretical calculation, the (001) facet was screened as the superb facet of orthorhombic CoSe₂ for OER. Afterwards, CoSe₂(001) nanosheets were synthesized and the exposure ratio of (001) facet is controllable with thermodynamics methods effectively. The single-facet CoSe₂(001) delivered an overpotential as low as 240 mV at 10 mA·cm⁻² in 1 M KOH, which outperformed the bulk (380 mV) as well as other CoSe₂-base OER catalysts reported before. Especially, a shorter Co–Co path was observed in CoSe₂(001) by X­ray absorption spectroscopy. Further density functional theory (DFT) studies revealed that the reversible compression on the shorter Co–Co path could regulate the electronic structure of active sites during the OER process, and thus the energy barrier of the rate-determining step was reduced by 0.15 eV. This work could inspire more insights on the modification of electronic structure for OER electrocatalysts.