Chemically stable polypyrrole-modified liquid metal nanoparticles with the promising photothermal conversion capability

• PPy acts as a protected “armor” for elevated stability of EGaSn liquid metal. • Diverse synthetic strategy for structured EGaSn@PPy composite with regulated shape morphologies, size distribution, and oxidization degree. • The synergistic mechanism between EGaSn and PPy endows the composite a superior photothermal performance. • Failure analysis reveals that the higher stability of EGaSn@W-PPy results in better photothermal performance. The gallium-based eutectic alloy has gained particular attention in various fields due to its natural features of metallic fluids at room temperature. However, these alloy nanoparticles are extremely susceptible to be oxidized accompanied by de-alloying during the preparation, storage, and application. Here, with the assistance of the macromolecular stabilizer and dopant, sodium dodecylbenzene sulfonate (SDBS), we demonstrate a stable polypyrrole (PPy) layer acts as a protected “armor” on the surface of liquid metal ( i.e. , gallium-tin, EGaSn). SDBS enables the EGaSn to keep well dispersion and protects dispersed EGaSn from being durative oxidized before PPy coating. Furthermore, PPy greatly inhibits the oxidation of EGaSn owing to the strong interface interaction between the lone pair electrons around the N atoms of Py rings and the Ga 3+ orbit of EGaSn. Consequently, the fabricated EGaSn nanoparticles possess the features of smaller particle size, superior uniform distribution, and stronger antioxidant capacity. The prepared EGaSn@PPy composite exhibits superior stability even after storing in an aqueous solution for up to 100 days. As a proof-of-concept application, the EGaSn@PPy composite displays remarkable photothermal performance with an enhanced photothermal conversion efficiency. This work provides a novel surface engineering strategy to ameliorate liquid metal for photothermal therapy applications.