Biodegradable germanium nanoparticles as contrast agents for near-infrared-II photoacoustic imaging.

Photoacoustic (PA) imaging using contrast agents with strong near-infrared-II (NIR-II, 1000-1700 nm) absorption enables deep penetration into biological tissue. Besides, biocompatibility and biodegradability are essential for clinical translation. Herein, we developed biocompatible and biodegradable germanium nanoparticles (GeNPs) with high photothermal stability as well as strong and broad absorption for NIR-II PA imaging. We first demonstrate the excellent biocompatibility of the GeNPs through experiments, including the zebrafish embryo survival rates, nude mouse body weight curves, and histological images of the major organs. Then, comprehensive PA imaging demonstrations are presented to showcase the versatile imaging capabilities and excellent biodegradability, including