Biodegradable 2D GeP nanosheets with high photothermal conversion efficiency for multimodal cancer theranostics

Germanium phosphide (GeP), a new member of phosphorus-based 2D materials, is a semiconductor with indirect and narrowed band gap, which theoretically would have great potential to serve as near-infrared (NIR) photothermal agent (PTA) with high photothermal conversion efficiency (PTCE). However, the photothermal conversion performance and biomedical application of GeP-based nanocarriers has not been explored yet. Herein, we demonstrate the GeP nanosheets as high-performance PTA with PTCE of 68.6% in NIR region, which is much higher than many of other 2D PTA such as graphene, Mxenes, transition metal dichalcogenides, and black phosphorus (BP), and explore its application in multimodal cancer theranostics. Similar to BP nanosheets, the GeP nanosheets are biodegradable with excellent biocompatibility. With the merit of large specific surface area, the GeP nanosheets have high loading capacity (134 wt%) for anticancer drug Doxorubicin (DOX). The NH2-PEG-FA modified GeP-DOX hybrids show pH-responsive, heat-stimulative and sustained-drug-release performance as chemo-photothermal synergistic cancer therapy platform, and demonstrate remarkable tumor ablation ability both in vitro and in vivo. Meanwhile, multimodal imaging capability including photoacoustic imaging and photothermal imaging is also realized on basis of the excellent photothermal performance of GeP nanosheets. This study highlights the great promise of 2D GeP nanosheets as multifunctional platform for cancer theranostics application.