Mechanically Activated Solvent-Free Assembly of Ultrasmall Bi₂S₃ Nanoparticles: A Novel, Simple, and Sustainable Means To Access Chalcogenide Nanoparticles

Nanosized Bi 2 S 3 particles are one of the most promising nanomaterials for biomedical imaging, due to a unique combination of low toxicity and the high electron count of bismuth. However, the study and use of nano-sized Bi 2 S 3 have been prevented by major synthetic challenges, including sensitivity to air and harsh solvothermal conditions. Herein, we describe a novel and surprisingly simple pathway, based on solid-state bottom-up self-assembly, to access the elusive Bi 2 S 3 nanoparticles functionalized with surface ligands that allow dispersion in either organic or aqueous media. This one-pot, room-temperature synthesis utilizes mechanical activation in the solid state, either by milling or even manual grinding, to induce the spontaneous assembly of monodisperse 2 nm diameter nanoparticles applicable for CT imaging in physiological media. This solvent-free methodology utilizes readily available precursors to provide unprecedented one-step access to monodisperse nano-Bi 2 S 3 in multigram amounts, including polyethylene glycol (PEG)-coated nanoparticles, without the need for controlled atmospheres or solvothermal treatment.