Laser-ablative synthesis of stable size-tunable Bi nanoparticles and their functionalization for radiotherapy applications

Nanoformulations of high-Z elements can improve therapeutic outcome in radiotherapy-based treatment of tumors, but current nanomedicine implementations in radiotherapy still need biocompatible, non-toxic nano-agents exhibiting low polydispersity and high colloidal stability. Here, we elaborate methods of femtosecond (fs) laser ablation in water and organic solvents to fabricate stable aqueous colloidal solutions of ultrapure elemental Bi nanoparticles (NPs) and characterize them. We show that fs laser ablation of Bi target leads to the formation of spherical elemental Bi NPs having 25 nm mean size and wide size-dispersion. NPs prepared in water undergo fast conversion into 400-500 nm flake-like nanosheets, while NPs prepared in acetone demonstrate a high colloidal stability. We then employ methods of fs laser fragmentation to control mean size and size dispersion of Bi NPs. Stable aqueous solution of Bi NPs suitable for biomedical applications can be obtained by coating with Pluronic® F-127. We finally show that surface modification of Bi NPs increases its colloidal stability in phosphate buffer saline (PBS) solution by more than 6 fold. Exempt of any toxic synthetic by-products, laser-ablated Bi NPs present a novel appealing nanoplatform for image-guided combination photo- and radiotherapy.