This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. Two new triphenylarsonium alkylthiolate precursors, a thiosulfate zwitterion and a thioacetate salt, have been structurally characterised and their cytotoxicity evaluated against PC3 cells. The arsonium compounds have been used to prepare gold nanoparticles decorated with triphenylarsonium groups. Sheffield Hallam University and Indian Institute of Science (NL).