H2AX and neoplasm: To establish the correlation between photoacoustic lifetime-based oxygen images and γ-H2AX-stained histology results in a PDX breast cancer murine model after radiotherapy, an oxygen-sensing G2 polyacrylamide nanoparticle modified with a tumor-targeting F3 peptide, abbreviated as G2-PAA NPs, was injected into the tumor model to monitor the initial oxygen level and map its spatial distribution.